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git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux
Pull RCU updates from Joel Fernandes:
"NOCB CPU management:
- Consolidate rcu_nocb_cpu_offload() and rcu_nocb_cpu_deoffload() to
reduce code duplication
- Extract nocb_bypass_needs_flush() helper to reduce duplication in
NOCB bypass path
rcutorture/torture infrastructure:
- Add NOCB01 config for RCU_LAZY torture testing
- Add NOCB02 config for NOCB poll mode testing
- Add TRIVIAL-PREEMPT config for textbook-style preemptible RCU
torture
- Test call_srcu() with preemption both disabled and enabled
- Remove kvm-check-branches.sh in favor of kvm-series.sh
- Make hangs more visible in torture.sh output
- Add informative message for tests without a recheck file
- Fix numeric test comparison in srcu_lockdep.sh
- Use torture_shutdown_init() in refscale and rcuscale instead of
open-coded shutdown functions
- Fix modulo-zero error in torture_hrtimeout_ns().
SRCU:
- Fix SRCU read flavor macro comments
- Fix s/they disables/they disable/ typo in srcu_read_unlock_fast()
RCU Tasks:
- Document that RCU Tasks Trace grace periods now imply RCU grace
periods
- Remove unnecessary smp_store_release() in cblist_init_generic()"
* tag 'rcu.2026.03.31a' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux:
rcutorture: Test call_srcu() with preemption disabled and not
rcu: Add BOOTPARAM_RCU_STALL_PANIC Kconfig option
torture: Avoid modulo-zero error in torture_hrtimeout_ns()
rcu/nocb: Extract nocb_bypass_needs_flush() to reduce duplication
rcu/nocb: Consolidate rcu_nocb_cpu_offload/deoffload functions
rcu-tasks: Remove unnecessary smp_store_release() in cblist_init_generic()
rcutorture: Add NOCB02 config for nocb poll mode testing
rcutorture: Add NOCB01 config for RCU_LAZY torture testing
rcu-tasks: Document that RCU Tasks Trace grace periods now imply RCU grace periods
srcu: Fix s/they disables/they disable/ typo in srcu_read_unlock_fast()
srcu: Fix SRCU read flavor macro comments
rcuscale: Ditch rcu_scale_shutdown in favor of torture_shutdown_init()
refscale: Ditch ref_scale_shutdown in favor of torture_shutdown_init()
rcutorture: Fix numeric "test" comparison in srcu_lockdep.sh
torture: Print informative message for test without recheck file
torture: Make hangs more visible in torture.sh output
kvm-check-branches.sh: Remove in favor of kvm-series.sh
rcutorture: Add a textbook-style trivial preemptible RCU
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This commit tests invoking call_srcu() with preemption both enabled
and disabled, via acquiring of pi lock.
[ Joel: reword commit message. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
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Add a Kconfig option to set the default value of the
kernel.panic_on_rcu_stall sysctl, allowing the kernel to be built
with panic-on-RCU-stall enabled by default.
This is useful for high-availability systems that require automatic
recovery (via panic_timeout) when a CPU stall is detected, without
needing userspace to configure the sysctl at boot.
This follows the pattern established by BOOTPARAM_SOFTLOCKUP_PANIC
and BOOTPARAM_HUNG_TASK_PANIC. The runtime sysctl can still override
the Kconfig default.
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
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The bypass flush decision logic is duplicated in rcu_nocb_try_bypass()
and nocb_gp_wait() with similar conditions.
This commit therefore extracts the functionality into a common helper
function nocb_bypass_needs_flush() improving the code readability.
A flush_faster parameter is added to controlling the flushing thresholds
and timeouts. This design was in the original commit d1b222c6be1f
("rcu/nocb: Add bypass callback queueing") to avoid having the GP
kthread aggressively flush the bypass queue.
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
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The rcu_nocb_cpu_offload() and rcu_nocb_cpu_deoffload() functions are
nearly duplicates.
Therefore, extract the common logic into rcu_nocb_cpu_toggle_offload()
which takes an 'offload' boolean, and make both exported functions
simple wrappers.
This eliminates a bunch of duplicate code at the call sites, namely
mutex locking, CPU hotplug locking and CPU online checks.
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
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The cblist_init_generic() is executed during the CPU early boot
phase due to commit:30ef09635b9e ("rcu-tasks: Initialize callback
lists at rcu_init() time"), at this time, only one boot CPU is
online and the irq is disabled. this commit therefore use routine
assignment replace of smp_store_release() and WRITE_ONCE() in the
cblist_init_generic().
Signed-off-by: Zqiang <qiang.zhang@linux.dev>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
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The torture_shutdown_init() function spawns a shutdown kthread in
a manner very similar to that implemented by rcu_scale_shutdown().
This commit therefore re-implements rcu_scale_shutdown() in terms of
torture_shutdown_init().
This patch was generated by Claude given as input the patch making the
same transformation of ref_scale_shutdown().
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
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The torture_shutdown_init() function spawns a shutdown kthread in
a manner very similar to that implemented by ref_scale_shutdown().
This commit therefore re-implements ref_scale_shutdown in terms of
torture_shutdown_init().
The initial draft of this patch was generated by version 2.1.16 of the
Claude AI/LLM, but trained and configured for use by my employer, and
prompted to refer to Linux-kernel source code. This initial draft failed
to provide a forward reference to ref_scale_cleanup(), passed zero to
torture_shutdown_init() for an unwelcome insta-shutdown, and failed to
pass the kvm.sh --duration argument in as a refscale module parameter.
On the other hand, it did catch the need to NULL main_task on the
post-test self-shutdown code path, which I might well have forgotten
to do.
This version of the patch fixes those problems, and in fact very little
of the initial draft remains.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
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This commit adds a trivial textbook implementation of preemptible RCU
to rcutorture ("torture_type=trivial-preempt"), similar in spirit to the
existing "torture_type=trivial" textbook implementation of non-preemptible
RCU. Neither trivial RCU implementation has any value for production use,
and are intended only to keep Paul honest in his introductory writings
and presentations.
[ paulmck: Apply kernel test robot feedback. ]
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
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Tiny SRCU's srcu_gp_start_if_needed() directly calls schedule_work(),
which acquires the workqueue pool->lock.
This causes a lockdep splat when call_srcu() is called with a scheduler
lock held, due to:
call_srcu() [holding pi_lock]
srcu_gp_start_if_needed()
schedule_work() -> pool->lock
workqueue_init() / create_worker() [holding pool->lock]
wake_up_process() -> try_to_wake_up() -> pi_lock
Also add irq_work_sync() to cleanup_srcu_struct() to prevent a
use-after-free if a queued irq_work fires after cleanup begins.
Tested with rcutorture SRCU-T and no lockdep warnings.
[ Thanks to Boqun for similar fix in patch "rcu: Use an intermediate irq_work
to start process_srcu()" ]
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun@kernel.org>
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Since commit c27cea4416a3 ("rcu: Re-implement RCU Tasks Trace in terms
of SRCU-fast") we switched to SRCU in BPF. However as BPF instrument can
happen basically everywhere (including where a scheduler lock is held),
call_srcu() now needs to avoid acquiring scheduler lock because
otherwise it could cause deadlock [1]. Fix this by following what the
previous RCU Tasks Trace did: using an irq_work to delay the queuing of
the work to start process_srcu().
[boqun: Apply Joel's feedback]
[boqun: Apply Andrea's test feedback]
Reported-by: Andrea Righi <arighi@nvidia.com>
Closes: https://lore.kernel.org/all/abjzvz_tL_siV17s@gpd4/
Fixes: commit c27cea4416a3 ("rcu: Re-implement RCU Tasks Trace in terms of SRCU-fast")
Link: https://lore.kernel.org/rcu/3c4c5a29-24ea-492d-aeee-e0d9605b4183@nvidia.com/ [1]
Suggested-by: Zqiang <qiang.zhang@linux.dev>
Tested-by: Andrea Righi <arighi@nvidia.com>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun@kernel.org>
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When the srcutree.convert_to_big and srcutree.big_cpu_lim kernel boot
parameters specify initialization-time allocation of the srcu_node
tree for statically allocated srcu_struct structures (for example, in
DEFINE_SRCU() at build time instead of init_srcu_struct() at runtime),
init_srcu_struct_nodes() will attempt to dynamically allocate this tree
at the first run-time update-side use of this srcu_struct structure,
but while holding a raw spinlock. Because the memory allocator can
acquire non-raw spinlocks, this can result in lockdep splats.
This commit therefore uses the same SRCU_SIZE_ALLOC trick that is used
when the first run-time update-side use of this srcu_struct structure
happens before srcu_init() is called. The actual allocation then takes
place from workqueue context at the ends of upcoming SRCU grace periods.
[boqun: Adjust the sha1 of the Fixes tag]
Fixes: 175b45ed343a ("srcu: Use raw spinlocks so call_srcu() can be used under preempt_disable()")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun@kernel.org>
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Tree SRCU has used non-raw spinlocks for many years, motivated by a desire
to avoid unnecessary real-time latency and the absence of any reason to
use raw spinlocks. However, the recent use of SRCU in tracing as the
underlying implementation of RCU Tasks Trace means that call_srcu()
is invoked from preemption-disabled regions of code, which in turn
requires that any locks acquired by call_srcu() or its callees must be
raw spinlocks.
This commit therefore converts SRCU's spinlocks to raw spinlocks.
[boqun: Add Fixes tag]
Reported-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Fixes: c27cea4416a3 ("rcu: Re-implement RCU Tasks Trace in terms of SRCU-fast")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun@kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Conversion performed via this Coccinelle script:
// SPDX-License-Identifier: GPL-2.0-only
// Options: --include-headers-for-types --all-includes --include-headers --keep-comments
virtual patch
@gfp depends on patch && !(file in "tools") && !(file in "samples")@
identifier ALLOC = {kmalloc_obj,kmalloc_objs,kmalloc_flex,
kzalloc_obj,kzalloc_objs,kzalloc_flex,
kvmalloc_obj,kvmalloc_objs,kvmalloc_flex,
kvzalloc_obj,kvzalloc_objs,kvzalloc_flex};
@@
ALLOC(...
- , GFP_KERNEL
)
$ make coccicheck MODE=patch COCCI=gfp.cocci
Build and boot tested x86_64 with Fedora 42's GCC and Clang:
Linux version 6.19.0+ (user@host) (gcc (GCC) 15.2.1 20260123 (Red Hat 15.2.1-7), GNU ld version 2.44-12.fc42) #1 SMP PREEMPT_DYNAMIC 1970-01-01
Linux version 6.19.0+ (user@host) (clang version 20.1.8 (Fedora 20.1.8-4.fc42), LLD 20.1.8) #1 SMP PREEMPT_DYNAMIC 1970-01-01
Signed-off-by: Kees Cook <kees@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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This converts some of the visually simpler cases that have been split
over multiple lines. I only did the ones that are easy to verify the
resulting diff by having just that final GFP_KERNEL argument on the next
line.
Somebody should probably do a proper coccinelle script for this, but for
me the trivial script actually resulted in an assertion failure in the
middle of the script. I probably had made it a bit _too_ trivial.
So after fighting that far a while I decided to just do some of the
syntactically simpler cases with variations of the previous 'sed'
scripts.
The more syntactically complex multi-line cases would mostly really want
whitespace cleanup anyway.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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This was done entirely with mindless brute force, using
git grep -l '\<k[vmz]*alloc_objs*(.*, GFP_KERNEL)' |
xargs sed -i 's/\(alloc_objs*(.*\), GFP_KERNEL)/\1)/'
to convert the new alloc_obj() users that had a simple GFP_KERNEL
argument to just drop that argument.
Note that due to the extreme simplicity of the scripting, any slightly
more complex cases spread over multiple lines would not be triggered:
they definitely exist, but this covers the vast bulk of the cases, and
the resulting diff is also then easier to check automatically.
For the same reason the 'flex' versions will be done as a separate
conversion.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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This is the result of running the Coccinelle script from
scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to
avoid scalar types (which need careful case-by-case checking), and
instead replace kmalloc-family calls that allocate struct or union
object instances:
Single allocations: kmalloc(sizeof(TYPE), ...)
are replaced with: kmalloc_obj(TYPE, ...)
Array allocations: kmalloc_array(COUNT, sizeof(TYPE), ...)
are replaced with: kmalloc_objs(TYPE, COUNT, ...)
Flex array allocations: kmalloc(struct_size(PTR, FAM, COUNT), ...)
are replaced with: kmalloc_flex(*PTR, FAM, COUNT, ...)
(where TYPE may also be *VAR)
The resulting allocations no longer return "void *", instead returning
"TYPE *".
Signed-off-by: Kees Cook <kees@kernel.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace
Pull tracing updates from Steven Rostedt:
"User visible changes:
- Add an entry into MAINTAINERS file for RUST versions of code
There's now RUST code for tracing and static branches. To
differentiate that code from the C code, add entries in for the
RUST version (with "[RUST]" around it) so that the right
maintainers get notified on changes.
- New bitmask-list option added to tracefs
When this is set, bitmasks in trace event are not displayed as hex
numbers, but instead as lists: e.g. 0-5,7,9 instead of 0000015f
- New show_event_filters file in tracefs
Instead of having to search all events/*/*/filter for any active
filters enabled in the trace instance, the file show_event_filters
will list them so that there's only one file that needs to be
examined to see if any filters are active.
- New show_event_triggers file in tracefs
Instead of having to search all events/*/*/trigger for any active
triggers enabled in the trace instance, the file
show_event_triggers will list them so that there's only one file
that needs to be examined to see if any triggers are active.
- Have traceoff_on_warning disable trace pintk buffer too
Recently recording of trace_printk() could go to other trace
instances instead of the top level instance. But if
traceoff_on_warning triggers, it doesn't stop the buffer with
trace_printk() and that data can easily be lost by being
overwritten. Have traceoff_on_warning also disable the instance
that has trace_printk() being written to it.
- Update the hist_debug file to show what function the field uses
When CONFIG_HIST_TRIGGERS_DEBUG is enabled, a hist_debug file
exists for every event. This displays the internal data of any
histogram enabled for that event. But it is lacking the function
that is called to process one of its fields. This is very useful
information that was missing when debugging histograms.
- Up the histogram stack size from 16 to 31
Stack traces can be used as keys for event histograms. Currently
the size of the stack that is stored is limited to just 16 entries.
But the storage space in the histogram is 256 bytes, meaning that
it can store up to 31 entries (plus one for the count of entries).
Instead of letting that space go to waste, up the limit from 16 to
31. This makes the keys much more useful.
- Fix permissions of per CPU file buffer_size_kb
The per CPU file of buffer_size_kb was incorrectly set to read only
in a previous cleanup. It should be writable.
- Reset "last_boot_info" if the persistent buffer is cleared
The last_boot_info shows address information of a persistent ring
buffer if it contains data from a previous boot. It is cleared when
recording starts again, but it is not cleared when the buffer is
reset. The data is useless after a reset so clear it on reset too.
Internal changes:
- A change was made to allow tracepoint callbacks to have preemption
enabled, and instead be protected by SRCU. This required some
updates to the callbacks for perf and BPF.
perf needed to disable preemption directly in its callback because
it expects preemption disabled in the later code.
BPF needed to disable migration, as its code expects to run
completely on the same CPU.
- Have irq_work wake up other CPU if current CPU is "isolated"
When there's a waiter waiting on ring buffer data and a new event
happens, an irq work is triggered to wake up that waiter. This is
noisy on isolated CPUs (running NO_HZ_FULL). Trigger an IPI to a
house keeping CPU instead.
- Use proper free of trigger_data instead of open coding it in.
- Remove redundant call of event_trigger_reset_filter()
It was called immediately in a function that was called right after
it.
- Workqueue cleanups
- Report errors if tracing_update_buffers() were to fail.
- Make the enum update workqueue generic for other parts of tracing
On boot up, a work queue is created to convert enum names into
their numbers in the trace event format files. This work queue can
also be used for other aspects of tracing that takes some time and
shouldn't be called by the init call code.
The blk_trace initialization takes a bit of time. Have the
initialization code moved to the new tracing generic work queue
function.
- Skip kprobe boot event creation call if there's no kprobes defined
on cmdline
The kprobe initialization to set up kprobes if they are defined on
the cmdline requires taking the event_mutex lock. This can be held
by other tracing code doing initialization for a long time. Since
kprobes added to the kernel command line need to be setup
immediately, as they may be tracing early initialization code, they
cannot be postponed in a work queue and must be setup in the
initcall code.
If there's no kprobe on the kernel cmdline, there's no reason to
take the mutex and slow down the boot up code waiting to get the
lock only to find out there's nothing to do. Simply exit out early
if there's no kprobes on the kernel cmdline.
If there are kprobes on the cmdline, then someone cares more about
tracing over the speed of boot up.
- Clean up the trigger code a bit
- Move code out of trace.c and into their own files
trace.c is now over 11,000 lines of code and has become more
difficult to maintain. Start splitting it up so that related code
is in their own files.
Move all the trace_printk() related code into trace_printk.c.
Move the __always_inline stack functions into trace.h.
Move the pid filtering code into a new trace_pid.c file.
- Better define the max latency and snapshot code
The latency tracers have a "max latency" buffer that is a copy of
the main buffer and gets swapped with it when a new high latency is
detected. This keeps the trace up to the highest latency around
where this max_latency buffer is never written to. It is only used
to save the last max latency trace.
A while ago a snapshot feature was added to tracefs to allow user
space to perform the same logic. It could also enable events to
trigger a "snapshot" if one of their fields hit a new high. This
was built on top of the latency max_latency buffer logic.
Because snapshots came later, they were dependent on the latency
tracers to be enabled. In reality, the latency tracers depend on
the snapshot code and not the other way around. It was just that
they came first.
Restructure the code and the kconfigs to have the latency tracers
depend on snapshot code instead. This actually simplifies the logic
a bit and allows to disable more when the latency tracers are not
defined and the snapshot code is.
- Fix a "false sharing" in the hwlat tracer code
The loop to search for latency in hardware was using a variable
that could be changed by user space for each sample. If the user
change this variable, it could cause a bus contention, and reading
that variable can show up as a large latency in the trace causing a
false positive. Read this variable at the start of the sample with
a READ_ONCE() into a local variable and keep the code from sharing
cache lines with readers.
- Fix function graph tracer static branch optimization code
When only one tracer is defined for function graph tracing, it uses
a static branch to call that tracer directly. When another tracer
is added, it goes into loop logic to call all the registered
callbacks.
The code was incorrect when going back to one tracer and never
re-enabled the static branch again to do the optimization code.
- And other small fixes and cleanups"
* tag 'trace-v7.0' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (46 commits)
function_graph: Restore direct mode when callbacks drop to one
tracing: Fix indentation of return statement in print_trace_fmt()
tracing: Reset last_boot_info if ring buffer is reset
tracing: Fix to set write permission to per-cpu buffer_size_kb
tracing: Fix false sharing in hwlat get_sample()
tracing: Move d_max_latency out of CONFIG_FSNOTIFY protection
tracing: Better separate SNAPSHOT and MAX_TRACE options
tracing: Add tracer_uses_snapshot() helper to remove #ifdefs
tracing: Rename trace_array field max_buffer to snapshot_buffer
tracing: Move pid filtering into trace_pid.c
tracing: Move trace_printk functions out of trace.c and into trace_printk.c
tracing: Use system_state in trace_printk_init_buffers()
tracing: Have trace_printk functions use flags instead of using global_trace
tracing: Make tracing_update_buffers() take NULL for global_trace
tracing: Make printk_trace global for tracing system
tracing: Move ftrace_trace_stack() out of trace.c and into trace.h
tracing: Move __trace_buffer_{un}lock_*() functions to trace.h
tracing: Make tracing_selftest_running global to the tracing subsystem
tracing: Make tracing_disabled global for tracing system
tracing: Clean up use of trace_create_maxlat_file()
...
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SRCU-fast is designed to be used in NMI handlers, even going so far
as to use atomic operations for architectures supporting NMIs but not
providing NMI-safe per-CPU atomic operations. However, the WARN_ON_ONCE()
in __srcu_check_read_flavor() complains if SRCU-fast is used in an NMI
handler. This commit therefore modifies that WARN_ON_ONCE() to avoid
such complaints.
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: bpf@vger.kernel.org
Link: https://patch.msgid.link/8232efe8-a7a3-446c-af0b-19f9b523b4f7@paulmck-laptop
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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* rcu-nocb.20260123a:
rcu/nocb: Extract nocb_defer_wakeup_cancel() helper
rcu/nocb: Remove dead callback overload handling
rcu/nocb: Remove unnecessary WakeOvfIsDeferred wake path
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The pattern of checking nocb_defer_wakeup and deleting the timer is
duplicated in __wake_nocb_gp() and nocb_gp_wait(). Extract this into a
common helper function nocb_defer_wakeup_cancel().
This removes code duplication and makes it easier to maintain.
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
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During callback overload (exceeding qhimark), the NOCB code attempts
opportunistic advancement via rcu_advance_cbs_nowake(). Analysis shows
this code path is practically unreachable and serves no useful purpose.
Testing with 300,000 callback floods showed:
- 30 overload conditions triggered
- 0 advancements actually occurred
While a theoretical window exists where this code could execute (e.g.,
vCPU preemption between gp_seq update and rcu_nocb_gp_cleanup()), even
if it did, the advancement would be redundant. The rcuog kthread must
still run to wake the rcuoc callback thread - we would just be
duplicating work that rcuog will perform when it finally gets to run.
Since this path provides no meaningful benefit and extensive testing
confirms it is never useful, remove it entirely.
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
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The WakeOvfIsDeferred code path in __call_rcu_nocb_wake() attempts to
wake rcuog when the callback count exceeds qhimark and callbacks aren't
done with their GP (newly queued or awaiting GP). However, a lot of
testing proves this wake is always redundant or useless.
In the flooding case, rcuog is always waiting for a GP to finish. So
waking up the rcuog thread is pointless. The timer wakeup adds overhead,
rcuog simply wakes up and goes back to sleep achieving nothing.
This path also adds a full memory barrier, and additional timer expiry
modifications unnecessarily.
The root cause is that WakeOvfIsDeferred fires when
!rcu_segcblist_ready_cbs() (GP not complete), but waking rcuog cannot
accelerate GP completion.
This commit therefore removes this path.
Tested with rcutorture scenarios: TREE01, TREE05, TREE08 (all NOCB
configurations) - all pass. Also stress tested using a kernel module
that floods call_rcu() to trigger the overload conditions and made the
observations confirming the findings.
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
|
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* rcu-misc.20260111a:
rcu: Reduce synchronize_rcu() latency by reporting GP kthread's CPU QS early
srcu: Use suitable gfp_flags for the init_srcu_struct_nodes()
rcu: Fix rcu_read_unlock() deadloop due to softirq
rcutorture: Correctly compute probability to invoke ->exp_current()
rcu: Make expedited RCU CPU stall warnings detect stall-end races
|
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The RCU grace period mechanism uses a two-phase FQS (Force Quiescent
State) design where the first FQS saves dyntick-idle snapshots and
the second FQS compares them. This results in long and unnecessary latency
for synchronize_rcu() on idle systems (two FQS waits of ~3ms each with
1000HZ) whenever one FQS wait sufficed.
Some investigations showed that the GP kthread's CPU is the holdout CPU
a lot of times after the first FQS as - it cannot be detected as "idle"
because it's actively running the FQS scan in the GP kthread.
Therefore, at the end of rcu_gp_init(), immediately report a quiescent
state for the GP kthread's CPU using rcu_qs() + rcu_report_qs_rdp(). The
GP kthread cannot be in an RCU read-side critical section while running
GP initialization, so this is safe and results in significant latency
improvements.
The following tests were performed:
(1) synchronize_rcu() benchmarking
100 synchronize_rcu() calls with 32 CPUs, 10 runs each (default fqs
jiffies settings):
Baseline (without fix):
| Run | Mean | Min | Max |
|-----|-----------|----------|-----------|
| 1 | 10.088 ms | 9.989 ms | 18.848 ms |
| 2 | 10.064 ms | 9.982 ms | 16.470 ms |
| 3 | 10.051 ms | 9.988 ms | 15.113 ms |
| 4 | 10.125 ms | 9.929 ms | 22.411 ms |
| 5 | 8.695 ms | 5.996 ms | 15.471 ms |
| 6 | 10.157 ms | 9.977 ms | 25.723 ms |
| 7 | 10.102 ms | 9.990 ms | 20.224 ms |
| 8 | 8.050 ms | 5.985 ms | 10.007 ms |
| 9 | 10.059 ms | 9.978 ms | 15.934 ms |
| 10 | 10.077 ms | 9.984 ms | 17.703 ms |
With fix:
| Run | Mean | Min | Max |
|-----|----------|----------|-----------|
| 1 | 6.027 ms | 5.915 ms | 8.589 ms |
| 2 | 6.032 ms | 5.984 ms | 9.241 ms |
| 3 | 6.010 ms | 5.986 ms | 7.004 ms |
| 4 | 6.076 ms | 5.993 ms | 10.001 ms |
| 5 | 6.084 ms | 5.893 ms | 10.250 ms |
| 6 | 6.034 ms | 5.908 ms | 9.456 ms |
| 7 | 6.051 ms | 5.993 ms | 10.000 ms |
| 8 | 6.057 ms | 5.941 ms | 10.001 ms |
| 9 | 6.016 ms | 5.927 ms | 7.540 ms |
| 10 | 6.036 ms | 5.993 ms | 9.579 ms |
Summary:
- Mean latency: 9.75 ms -> 6.04 ms (38% improvement)
- Max latency: 25.72 ms -> 10.25 ms (60% improvement)
(2) Bridge setup/teardown latency (Uladzislau Rezki)
x86_64 with 64 CPUs, 100 iterations of bridge add/configure/delete:
real time
1 - default: 24.221s
2 - this patch: 20.754s (14% faster)
3 - this patch + wake_from_gp: 15.895s (34% faster)
4 - wake_from_gp only: 18.947s (22% faster)
Per-synchronize_rcu() latency (in usec):
1 2 3 4
median: 37249.5 31540.5 15765 22480
min: 7881 7918 9803 7857
max: 63651 55639 31861 32040
This patch combined with rcu_normal_wake_from_gp reduces bridge
setup/teardown time from 24 seconds to 16 seconds.
(3) CPU overhead verification (Uladzislau Rezki)
System CPU time across 5 runs showed no measurable increase:
default: 1.698s - 1.937s
this patch: 1.667s - 1.930s
Conclusion: variations are within noise, no CPU overhead regression.
(4) rcutorture
Tested TREE and SRCU configurations - no regressions.
Reviewed-by: "Paul E. McKenney" <paulmck@kernel.org>
Tested-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Samir M <samir@linux.ibm.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
|
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For use the init_srcu_struct*() to initialized srcu structure,
the srcu structure's->srcu_sup and sda use GFP_KERNEL flags to
allocate memory. similarly, if set SRCU_SIZING_INIT, the
srcu_sup's->node can still use GFP_KERNEL flags to allocate
memory, not need to use GFP_ATOMIC flags all the time.
Signed-off-by: Zqiang <qiang.zhang@linux.dev>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
|
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Commit 5f5fa7ea89dc ("rcu: Don't use negative nesting depth in
__rcu_read_unlock()") removes the recursion-protection code from
__rcu_read_unlock(). Therefore, we could invoke the deadloop in
raise_softirq_irqoff() with ftrace enabled as follows:
WARNING: CPU: 0 PID: 0 at kernel/trace/trace.c:3021 __ftrace_trace_stack.constprop.0+0x172/0x180
Modules linked in: my_irq_work(O)
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Tainted: G O 6.18.0-rc7-dirty #23 PREEMPT(full)
Tainted: [O]=OOT_MODULE
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
RIP: 0010:__ftrace_trace_stack.constprop.0+0x172/0x180
RSP: 0018:ffffc900000034a8 EFLAGS: 00010002
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 0000000000000000
RDX: 0000000000000003 RSI: ffffffff826d7b87 RDI: ffffffff826e9329
RBP: 0000000000090009 R08: 0000000000000005 R09: ffffffff82afbc4c
R10: 0000000000000008 R11: 0000000000011d7a R12: 0000000000000000
R13: ffff888003874100 R14: 0000000000000003 R15: ffff8880038c1054
FS: 0000000000000000(0000) GS:ffff8880fa8ea000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055b31fa7f540 CR3: 00000000078f4005 CR4: 0000000000770ef0
PKRU: 55555554
Call Trace:
<IRQ>
trace_buffer_unlock_commit_regs+0x6d/0x220
trace_event_buffer_commit+0x5c/0x260
trace_event_raw_event_softirq+0x47/0x80
raise_softirq_irqoff+0x6e/0xa0
rcu_read_unlock_special+0xb1/0x160
unwind_next_frame+0x203/0x9b0
__unwind_start+0x15d/0x1c0
arch_stack_walk+0x62/0xf0
stack_trace_save+0x48/0x70
__ftrace_trace_stack.constprop.0+0x144/0x180
trace_buffer_unlock_commit_regs+0x6d/0x220
trace_event_buffer_commit+0x5c/0x260
trace_event_raw_event_softirq+0x47/0x80
raise_softirq_irqoff+0x6e/0xa0
rcu_read_unlock_special+0xb1/0x160
unwind_next_frame+0x203/0x9b0
__unwind_start+0x15d/0x1c0
arch_stack_walk+0x62/0xf0
stack_trace_save+0x48/0x70
__ftrace_trace_stack.constprop.0+0x144/0x180
trace_buffer_unlock_commit_regs+0x6d/0x220
trace_event_buffer_commit+0x5c/0x260
trace_event_raw_event_softirq+0x47/0x80
raise_softirq_irqoff+0x6e/0xa0
rcu_read_unlock_special+0xb1/0x160
unwind_next_frame+0x203/0x9b0
__unwind_start+0x15d/0x1c0
arch_stack_walk+0x62/0xf0
stack_trace_save+0x48/0x70
__ftrace_trace_stack.constprop.0+0x144/0x180
trace_buffer_unlock_commit_regs+0x6d/0x220
trace_event_buffer_commit+0x5c/0x260
trace_event_raw_event_softirq+0x47/0x80
raise_softirq_irqoff+0x6e/0xa0
rcu_read_unlock_special+0xb1/0x160
__is_insn_slot_addr+0x54/0x70
kernel_text_address+0x48/0xc0
__kernel_text_address+0xd/0x40
unwind_get_return_address+0x1e/0x40
arch_stack_walk+0x9c/0xf0
stack_trace_save+0x48/0x70
__ftrace_trace_stack.constprop.0+0x144/0x180
trace_buffer_unlock_commit_regs+0x6d/0x220
trace_event_buffer_commit+0x5c/0x260
trace_event_raw_event_softirq+0x47/0x80
__raise_softirq_irqoff+0x61/0x80
__flush_smp_call_function_queue+0x115/0x420
__sysvec_call_function_single+0x17/0xb0
sysvec_call_function_single+0x8c/0xc0
</IRQ>
Commit b41642c87716 ("rcu: Fix rcu_read_unlock() deadloop due to IRQ work")
fixed the infinite loop in rcu_read_unlock_special() for IRQ work by
setting a flag before calling irq_work_queue_on(). We fix this issue by
setting the same flag before calling raise_softirq_irqoff() and rename the
flag to defer_qs_pending for more common.
Fixes: 5f5fa7ea89dc ("rcu: Don't use negative nesting depth in __rcu_read_unlock()")
Reported-by: Tengda Wu <wutengda2@huawei.com>
Signed-off-by: Yao Kai <yaokai34@huawei.com>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
|
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Lack of parentheses causes the ->exp_current() function, for example,
srcu_expedite_current(), to be called only once in four billion times
instead of the intended once in 256 times. This commit therefore adds
the needed parentheses.
Reported-by: Chris Mason <clm@meta.com>
Reported-by: Joel Fernandes <joelagnelf@nvidia.com>
Fixes: 950063c6e897 ("rcutorture: Test srcu_expedite_current()")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
|
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If an expedited RCU CPU stall ends just at the stall-warning timeout,
the current code will print an expedited stall-warning message, but one
that doesn't identify any CPUs or tasks causing the stall. This is most
likely to happen for short-timeout stalls, for example, the 20-millisecond
timeouts that are sometimes used for small embedded devices. Needless to
say, these semi-empty stall-warning messages can be rather confusing.
One option would be to suppress the stall-warning message entirely in
this case, but the near-miss information can be quite valuable.
Detect this race condition and emits a "INFO: Expedited stall ended
before state dump start" message to clarify matters.
[boqun: Apply feedback from Borislav]
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
|
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* rcu-torture.20260104a:
rcutorture: Add --kill-previous option to terminate previous kvm.sh runs
rcutorture: Prevent concurrent kvm.sh runs on same source tree
torture: Include commit discription in testid.txt
torture: Make config2csv.sh properly handle comments in .boot files
torture: Make kvm-series.sh give run numbers and totals
torture: Make kvm-series.sh give build numbers and totals
torture: Parallelize kvm-series.sh guest-OS execution
rcutorture: Add context checks to rcu_torture_timer()
|
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This commit adds irq, NMI, and softirq context checks to the
rcu_torture_timer() function. Just because you are paranoid does not
mean that they are not out to get you... ;-)
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
|
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This commit adds a ->exp_current member to the tasks_tracing_ops structure
to test the rcu_tasks_trace_expedite_current() function.
[ paulmck: Apply kernel test robot feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: bpf@vger.kernel.org
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
|
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When expressing RCU Tasks Trace in terms of SRCU-fast, it was
necessary to keep a nesting count and per-CPU srcu_ctr structure
pointer in the task_struct structure, which is slow to access.
But an alternative is to instead make rcu_read_lock_tasks_trace() and
rcu_read_unlock_tasks_trace(), which match the underlying SRCU-fast
semantics, avoiding the task_struct accesses.
When all callers have switched to the new API, the previous
rcu_read_lock_trace() and rcu_read_unlock_trace() APIs will be removed.
The rcu_read_{,un}lock_{,tasks_}trace() functions need to use smp_mb()
only if invoked where RCU is not watching, that is, from locations where
a call to rcu_is_watching() would return false. In architectures that
define the ARCH_WANTS_NO_INSTR Kconfig option, use of noinstr and friends
ensures that tracing happens only where RCU is watching, so those
architectures can dispense entirely with the read-side calls to smp_mb().
Other architectures include these read-side calls by default, but in many
installations there might be either larger than average tolerance for
risk, prohibition of removing tracing on a running system, or careful
review and approval of removing of tracing. Such installations can
build their kernels with CONFIG_TASKS_TRACE_RCU_NO_MB=y to avoid those
read-side calls to smp_mb(), thus accepting responsibility for run-time
removal of tracing from code regions that RCU is not watching.
Those wishing to disable read-side memory barriers for an entire
architecture can select this TASKS_TRACE_RCU_NO_MB Kconfig option,
hence the polarity.
[ paulmck: Apply Peter Zijlstra feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: bpf@vger.kernel.org
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
|
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Moving the rcu_tasks_trace_srcu_struct structure instance out
from under the CONFIG_TASKS_RCU_GENERIC Kconfig option permits
the CONFIG_TASKS_TRACE_RCU Kconfig option to stop enabling this
CONFIG_TASKS_RCU_GENERIC Kconfig option. This commit also therefore
makes it so.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: bpf@vger.kernel.org
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
|
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Now that RCU Tasks Trace has been re-implemented in terms of SRCU-fast,
the ->trc_ipi_to_cpu, ->trc_blkd_cpu, ->trc_blkd_node, ->trc_holdout_list,
and ->trc_reader_special task_struct fields are no longer used.
In addition, the rcu_tasks_trace_qs(), rcu_tasks_trace_qs_blkd(),
exit_tasks_rcu_finish_trace(), and rcu_spawn_tasks_trace_kthread(),
show_rcu_tasks_trace_gp_kthread(), rcu_tasks_trace_get_gp_data(),
rcu_tasks_trace_torture_stats_print(), and get_rcu_tasks_trace_gp_kthread()
functions and all the other functions that they invoke are no longer used.
Also, the TRC_NEED_QS and TRC_NEED_QS_CHECKED CPP macros are no longer used.
Neither are the rcu_tasks_trace_lazy_ms and rcu_task_ipi_delay rcupdate
module parameters and the TASKS_TRACE_RCU_READ_MB Kconfig option.
This commit therefore removes all of them.
[ paulmck: Apply Alexei Starovoitov feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: bpf@vger.kernel.org
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
|
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This commit saves more than 500 lines of RCU code by re-implementing
RCU Tasks Trace in terms of SRCU-fast. Follow-up work will remove
more code that does not cause problems by its presence, but that is no
longer required.
This variant places smp_mb() in rcu_read_{,un}lock_trace(), and in the
same place that srcu_read_{,un}lock() would put them. These smp_mb()
calls will be removed on common-case architectures in a later commit.
In the meantime, it serves to enforce ordering between the underlying
srcu_read_{,un}lock_fast() markers and the intervening critical section,
even on architectures that permit attaching tracepoints on regions of
code not watched by RCU. Such architectures defeat SRCU-fast's use of
implicit single-instruction, interrupts-disabled, and atomic-operation
RCU read-side critical sections, which have no effect when RCU is not
watching. The aforementioned later commit will insert these smp_mb()
calls only on architectures that have not used noinstr to prevent
attaching tracepoints to code where RCU is not watching.
[ paulmck: Apply kernel test robot, Boqun Feng, and Zqiang feedback. ]
[ paulmck: Split out Tiny SRCU fixes per Andrii Nakryiko feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: kernel test robot <oliver.sang@intel.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: bpf@vger.kernel.org
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
|
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git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux
Pull RCU updates from Frederic Weisbecker:
"SRCU:
- Properly handle SRCU readers within IRQ disabled sections in tiny
SRCU
- Preparation to reimplement RCU Tasks Trace on top of SRCU fast:
- Introduce API to expedite a grace period and test it through
rcutorture
- Split srcu-fast in two flavours: SRCU-fast and SRCU-fast-updown.
Both are still targeted toward faster readers (without full
barriers on LOCK and UNLOCK) at the expense of heavier write
side (using full RCU grace period ordering instead of simply
full ordering) as compared to "traditional" non-fast SRCU. But
those srcu-fast flavours are going to be optimized in two
different ways:
- SRCU-fast will become the reimplementation basis for
RCU-TASK-TRACE for consolidation. Since RCU-TASK-TRACE must
be NMI safe, SRCU-fast must be as well.
- SRCU-fast-updown will be needed for uretprobes code in order
to get rid of the read-side memory barriers while still
allowing entering the reader at task level while exiting it
in a timer handler. It is considered semaphore-like in that
it can have different owners between LOCK and UNLOCK.
However it is not NMI-safe.
The actual optimizations are work in progress for the next
cycle. Only the new interfaces are added for now, along with
related torture and scalability test code.
- Create/document/debug/torture new proper initializers for RCU fast:
DEFINE_SRCU_FAST() and init_srcu_struct_fast()
This allows for using right away the proper ordering on the write
side (either full ordering or full RCU grace period ordering)
without waiting for the read side to tell which to use.
This also optimizes the read side altogether with moving flavour
debug checks under debug config and with removing a costly RmW
operation on their first call.
- Make some diagnostic functions tracing safe
Refscale:
- Add performance testing for common context synchronizations
(Preemption, IRQ, Softirq) and per-cpu increments. Those are
relevant comparisons against SRCU-fast read side APIs, especially
as they are planned to synchronize further tracing fast-path code
Miscellanous:
- In order to prepare the layout for nohz_full work deferral to user
exit, the context tracking state must shrink the counter of
transitions to/from RCU not watching. The only possible hazard is
to trigger wrap-around more easily, delaying a bit grace periods
when that happens. This should be a rare event though. Yet add
debugging and torture code to test that assumption
- Fix memory leak on locktorture module
- Annotate accesses in rculist_nulls.h to prevent from KCSAN
warnings. On recent discussions, we also concluded that all those
WRITE_ONCE() and READ_ONCE() on list APIs deserve appropriate
comments. Something to be expected for the next cycle
- Provide a script to apply several configs to several commits with
torture
- Allow torture to reuse a build directory in order to save needless
rebuild time
- Various cleanups"
* tag 'rcu.release.v6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: (29 commits)
refscale: Add SRCU-fast-updown readers
refscale: Exercise DEFINE_STATIC_SRCU_FAST() and init_srcu_struct_fast()
rcutorture: Make srcu{,d}_torture_init() announce the SRCU type
srcu: Create an SRCU-fast-updown API
refscale: Do not disable interrupts for tests involving local_bh_enable()
refscale: Add non-atomic per-CPU increment readers
refscale: Add this_cpu_inc() readers
refscale: Add preempt_disable() readers
refscale: Add local_bh_disable() readers
refscale: Add local_irq_disable() and local_irq_save() readers
torture: Permit negative kvm.sh --kconfig numberic arguments
srcu: Add SRCU_READ_FLAVOR_FAST_UPDOWN CPP macro
rcu: Mark diagnostic functions as notrace
rcutorture: Make TREE04 use CONFIG_RCU_DYNTICKS_TORTURE
rcutorture: Remove redundant rcutorture_one_extend() from rcu_torture_one_read()
rcutorture: Permit kvm-again.sh to re-use the build directory
torture: Add kvm-series.sh to test commit/scenario combination
rcu: use WRITE_ONCE() for ->next and ->pprev of hlist_nulls
locktorture: Fix memory leak in param_set_cpumask()
doc: Update for SRCU-fast definitions and initialization
...
|
|
- In order to prepare the layout for nohz_full work deferral to
user exit, the context tracking state must shrink the counter
of transitions to/from RCU not watching. The only possible hazard
is to trigger wrap-around more easily, delaying a bit grace periods
when that happens. This should be a rare event though. Yet add
debugging and torture code to test that assumption.
- Fix memory leak on locktorture module
- Annotate accesses in rculist_nulls.h to prevent from KCSAN warnings.
On recent discussions, we also concluded that all those WRITE_ONCE()
and READ_ONCE() on list APIs deserve appropriate comments. Something
to be expected for the next cycle.
- Provide a script to apply several configs to several commits with torture.
- Allow torture to reuse a build directory in order to save needless
rebuild time.
- Various cleanups.
|
|
Add performance testing for common context synchronizations
(Preemption, IRQ, Softirq) and per-cpu increments. Those are
relevant comparisons against SRCU-fast read side APIs, especially
as they are planned to synchronize further tracing fast-path code.
|
|
This commit adds refscale readers based on srcu_read_lock_fast_updown()
and srcu_read_unlock_fast_updown()
("refscale.scale_type=srcu-fast-updown"). On my x86 laptop, these are
about 2.2ns per pair.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: <bpf@vger.kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
|
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This commit updates the initialization for the "srcu-fast" scale
type to use DEFINE_STATIC_SRCU_FAST() when reader_flavor is equal to
SRCU_READ_FLAVOR_FAST.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: <bpf@vger.kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
|
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This commit causes rcutorture's srcu_torture_init() and
srcud_torture_init() functions to announce on the console log
which variant of SRCU is being tortured, for example: "torture:
srcud_torture_init fast SRCU".
[ paulmck: Apply feedback from kernel test robot. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
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This commit creates an SRCU-fast-updown API, including
DEFINE_SRCU_FAST_UPDOWN(), DEFINE_STATIC_SRCU_FAST_UPDOWN(),
__init_srcu_struct_fast_updown(), init_srcu_struct_fast_updown(),
srcu_read_lock_fast_updown(), srcu_read_unlock_fast_updown(),
__srcu_read_lock_fast_updown(), and __srcu_read_unlock_fast_updown().
These are initially identical to their SRCU-fast counterparts, but both
SRCU-fast and SRCU-fast-updown will be optimized in different directions
by later commits. SRCU-fast will lack any sort of srcu_down_read() and
srcu_up_read() APIs, which will enable extremely efficient NMI safety.
For its part, SRCU-fast-updown will not be NMI safe, which will enable
reasonably efficient implementations of srcu_down_read_fast() and
srcu_up_read_fast().
This API fork happens to meet two different future use cases.
* SRCU-fast will become the reimplementation basis for RCU-TASK-TRACE
for consolidation. Since RCU-TASK-TRACE must be NMI safe, SRCU-fast
must be as well.
* SRCU-fast-updown will be needed for uretprobes code in order to get
rid of the read-side memory barriers while still allowing entering the
reader at task level while exiting it in a timer handler.
This commit also adds rcutorture tests for the new APIs. This
(annoyingly) needs to be in the same commit for bisectability. With this
commit, the 0x8 value tests SRCU-fast-updown. However, most SRCU-fast
testing will be via the RCU Tasks Trace wrappers.
[ paulmck: Apply s/0x8/0x4/ missing change per Boqun Feng feedback. ]
[ paulmck: Apply Akira Yokosawa feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: <bpf@vger.kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
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set_tsk_need_resched(current) requires set_preempt_need_resched(current) to
work correctly outside of the scheduler.
Provide set_need_resched_current() which wraps this correctly and replace
all the open coded instances.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://patch.msgid.link/20251116174750.665769842@linutronix.de
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Some kernel configurations prohibit invoking local_bh_enable() while
interrupts are disabled. However, refscale disables interrupts to reduce
OS noise during the tests, which results in splats. This commit therefore
adds an ->enable_irqs flag to the ref_scale_ops structure, and refrains
from disabling interrupts when that flag is set. This flag is set for
the "bh" and "incpercpubh" scale_type module-parameter values.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
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This commit adds refscale readers based on READ_ONCE() and WRITE_ONCE()
that are unprotected (can lose counts, "refscale.scale_type=incpercpu"),
preempt-disabled ("refscale.scale_type=incpercpupreempt"),
bh-disabled ("refscale.scale_type=incpercpubh"), and irq-disabled
("refscale.scale_type=incpercpuirqsave"). On my x86 laptop, these are
about 4.3ns, 3.8ns, and 7.3ns per pair, respectively.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
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This commit adds refscale readers based on this_cpu_inc() and
this_cpu_inc() ("refscale.scale_type=percpuinc"). On my x86 laptop,
these are about 4.5ns per pair.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
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This commit adds refscale readers based on preempt_disable() and
preempt_enable() ("refscale.scale_type=preempt"). On my x86 laptop, these
are about 2.8ns.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
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This commit adds refscale readers based on local_bh_disable() and
local_bh_enable() ("refscale.scale_type=bh"). On my x86 laptop, these
are about 4.9ns.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
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This commit adds refscale readers based on local_irq_disable() and
local_irq_enable() ("refscale.scale_type=irq") and on local_irq_save()
and local_irq_restore ("refscale.scale_type=irqsave"). On my x86 laptop,
these are about 2.8ns and 7.5ns per enable/disable pair, respectively.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
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