linux/kernel/module.c, branch v3.19-rc2

Merge tag 'modules-next-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux

2014-12-19T04:55:41Z

Pull module updates from Rusty Russell: "The exciting thing here is the getting rid of stop_machine on module removal. This is possible by using a simple atomic_t for the counter, rather than our fancy per-cpu counter: it turns out that no one is doing a module increment per net packet, so the slowdown should be in the noise" * tag 'modules-next-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux: param: do not set store func without write perm params: cleanup sysfs allocation kernel:module Fix coding style errors and warnings. module: Remove stop_machine from module unloading module: Replace module_ref with atomic_t refcnt lib/bug: Use RCU list ops for module_bug_list module: Unlink module with RCU synchronizing instead of stop_machine module: Wait for RCU synchronizing before releasing a module

kernel:module Fix coding style errors and warnings.

2014-11-11T06:37:47Z

Fixed codin style errors and warnings. Changes printk with print_debug/warn. Changed seq_printf to seq_puts. Signed-off-by: Ionut Alexa Signed-off-by: Rusty Russell (removed bogus KERN_DEFAULT conversion)

module: Remove stop_machine from module unloading

2014-11-11T06:37:46Z

Remove stop_machine from module unloading by adding new reference counting algorithm. This atomic refcounter works like a semaphore, it can get (be incremented) only when the counter is not 0. When loading a module, kmodule subsystem sets the counter MODULE_REF_BASE (= 1). And when unloading the module, it subtracts MODULE_REF_BASE from the counter. If no one refers the module, the refcounter becomes 0 and we can remove the module safely. If someone referes it, we try to recover the counter by adding MODULE_REF_BASE unless the counter becomes 0, because the referrer can put the module right before recovering. If the recovering is failed, we can get the 0 refcount and it never be incremented again, it can be removed safely too. Note that __module_get() forcibly gets the module refcounter, users should use try_module_get() instead of that. Signed-off-by: Masami Hiramatsu Signed-off-by: Rusty Russell

module: Replace module_ref with atomic_t refcnt

2014-11-11T06:37:46Z

Replace module_ref per-cpu complex reference counter with an atomic_t simple refcnt. This is for code simplification. Signed-off-by: Masami Hiramatsu Signed-off-by: Rusty Russell

lib/bug: Use RCU list ops for module_bug_list

2014-11-11T06:37:46Z

Actually since module_bug_list should be used in BUG context, we may not need this. But for someone who want to use this from normal context, this makes module_bug_list an RCU list. Signed-off-by: Masami Hiramatsu Signed-off-by: Rusty Russell

module: Unlink module with RCU synchronizing instead of stop_machine

2014-11-11T06:37:45Z

Unlink module from module list with RCU synchronizing instead of using stop_machine(). Since module list is already protected by rcu, we don't need stop_machine() anymore. Signed-off-by: Masami Hiramatsu Signed-off-by: Rusty Russell

module: Wait for RCU synchronizing before releasing a module

2014-11-11T06:37:44Z

Wait for RCU synchronizing on failure path of module loading before releasing struct module, because the memory of mod->list can still be accessed by list walkers (e.g. kallsyms). Signed-off-by: Masami Hiramatsu Signed-off-by: Rusty Russell

sched, modules: Fix nested sleep in add_unformed_module()

2014-10-28T09:56:30Z

This is a genuine bug in add_unformed_module(), we cannot use blocking primitives inside a wait loop. So rewrite the wait_event_interruptible() usage to use the fresh wait_woken() stuff. Reported-by: Fengguang Wu Signed-off-by: Peter Zijlstra (Intel) Cc: tglx@linutronix.de Cc: ilya.dryomov@inktank.com Cc: umgwanakikbuti@gmail.com Cc: Rusty Russell Cc: oleg@redhat.com Cc: Linus Torvalds Cc: Andrew Morton Cc: Greg Kroah-Hartman Link: http://lkml.kernel.org/r/20140924082242.458562904@infradead.org [ So this is probably complex to backport and the race wasn't reported AFAIK, so not marked for -stable. ] Signed-off-by: Ingo Molnar Signed-off-by: Ingo Molnar

Merge tag 'modules-next-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux

2014-10-18T17:24:26Z

Pull module fix from Rusty Russell: "A single panic fix for a rare race, stable CC'd" * tag 'modules-next-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux: modules, lock around setting of MODULE_STATE_UNFORMED

modules, lock around setting of MODULE_STATE_UNFORMED

2014-10-14T23:50:09Z

A panic was seen in the following sitation. There are two threads running on the system. The first thread is a system monitoring thread that is reading /proc/modules. The second thread is loading and unloading a module (in this example I'm using my simple dummy-module.ko). Note, in the "real world" this occurred with the qlogic driver module. When doing this, the following panic occurred: ------------[ cut here ]------------ kernel BUG at kernel/module.c:3739! invalid opcode: 0000 [#1] SMP Modules linked in: binfmt_misc sg nfsv3 rpcsec_gss_krb5 nfsv4 dns_resolver nfs fscache intel_powerclamp coretemp kvm_intel kvm crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel aesni_intel lrw igb gf128mul glue_helper iTCO_wdt iTCO_vendor_support ablk_helper ptp sb_edac cryptd pps_core edac_core shpchp i2c_i801 pcspkr wmi lpc_ich ioatdma mfd_core dca ipmi_si nfsd ipmi_msghandler auth_rpcgss nfs_acl lockd sunrpc xfs libcrc32c sr_mod cdrom sd_mod crc_t10dif crct10dif_common mgag200 syscopyarea sysfillrect sysimgblt i2c_algo_bit drm_kms_helper ttm isci drm libsas ahci libahci scsi_transport_sas libata i2c_core dm_mirror dm_region_hash dm_log dm_mod [last unloaded: dummy_module] CPU: 37 PID: 186343 Comm: cat Tainted: GF O-------------- 3.10.0+ #7 Hardware name: Intel Corporation S2600CP/S2600CP, BIOS RMLSDP.86I.00.29.D696.1311111329 11/11/2013 task: ffff8807fd2d8000 ti: ffff88080fa7c000 task.ti: ffff88080fa7c000 RIP: 0010:[] [] module_flags+0xb5/0xc0 RSP: 0018:ffff88080fa7fe18 EFLAGS: 00010246 RAX: 0000000000000003 RBX: ffffffffa03b5200 RCX: 0000000000000000 RDX: 0000000000001000 RSI: ffff88080fa7fe38 RDI: ffffffffa03b5000 RBP: ffff88080fa7fe28 R08: 0000000000000010 R09: 0000000000000000 R10: 0000000000000000 R11: 000000000000000f R12: ffffffffa03b5000 R13: ffffffffa03b5008 R14: ffffffffa03b5200 R15: ffffffffa03b5000 FS: 00007f6ae57ef740(0000) GS:ffff88101e7a0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000404f70 CR3: 0000000ffed48000 CR4: 00000000001407e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Stack: ffffffffa03b5200 ffff8810101e4800 ffff88080fa7fe70 ffffffff810d666c ffff88081e807300 000000002e0f2fbf 0000000000000000 ffff88100f257b00 ffffffffa03b5008 ffff88080fa7ff48 ffff8810101e4800 ffff88080fa7fee0 Call Trace: [] m_show+0x19c/0x1e0 [] seq_read+0x16e/0x3b0 [] proc_reg_read+0x3d/0x80 [] vfs_read+0x9c/0x170 [] SyS_read+0x58/0xb0 [] system_call_fastpath+0x16/0x1b Code: 48 63 c2 83 c2 01 c6 04 03 29 48 63 d2 eb d9 0f 1f 80 00 00 00 00 48 63 d2 c6 04 13 2d 41 8b 0c 24 8d 50 02 83 f9 01 75 b2 eb cb <0f> 0b 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48 89 e5 41 RIP [] module_flags+0xb5/0xc0 RSP Consider the two processes running on the system. CPU 0 (/proc/modules reader) CPU 1 (loading/unloading module) CPU 0 opens /proc/modules, and starts displaying data for each module by traversing the modules list via fs/seq_file.c:seq_open() and fs/seq_file.c:seq_read(). For each module in the modules list, seq_read does op->start() <-- this is a pointer to m_start() op->show() <- this is a pointer to m_show() op->stop() <-- this is a pointer to m_stop() The m_start(), m_show(), and m_stop() module functions are defined in kernel/module.c. The m_start() and m_stop() functions acquire and release the module_mutex respectively. ie) When reading /proc/modules, the module_mutex is acquired and released for each module. m_show() is called with the module_mutex held. It accesses the module struct data and attempts to write out module data. It is in this code path that the above BUG_ON() warning is encountered, specifically m_show() calls static char *module_flags(struct module *mod, char *buf) { int bx = 0; BUG_ON(mod->state == MODULE_STATE_UNFORMED); ... The other thread, CPU 1, in unloading the module calls the syscall delete_module() defined in kernel/module.c. The module_mutex is acquired for a short time, and then released. free_module() is called without the module_mutex. free_module() then sets mod->state = MODULE_STATE_UNFORMED, also without the module_mutex. Some additional code is called and then the module_mutex is reacquired to remove the module from the modules list: /* Now we can delete it from the lists */ mutex_lock(&module_mutex); stop_machine(__unlink_module, mod, NULL); mutex_unlock(&module_mutex); This is the sequence of events that leads to the panic. CPU 1 is removing dummy_module via delete_module(). It acquires the module_mutex, and then releases it. CPU 1 has NOT set dummy_module->state to MODULE_STATE_UNFORMED yet. CPU 0, which is reading the /proc/modules, acquires the module_mutex and acquires a pointer to the dummy_module which is still in the modules list. CPU 0 calls m_show for dummy_module. The check in m_show() for MODULE_STATE_UNFORMED passed for dummy_module even though it is being torn down. Meanwhile CPU 1, which has been continuing to remove dummy_module without holding the module_mutex, now calls free_module() and sets dummy_module->state to MODULE_STATE_UNFORMED. CPU 0 now calls module_flags() with dummy_module and ... static char *module_flags(struct module *mod, char *buf) { int bx = 0; BUG_ON(mod->state == MODULE_STATE_UNFORMED); and BOOM. Acquire and release the module_mutex lock around the setting of MODULE_STATE_UNFORMED in the teardown path, which should resolve the problem. Testing: In the unpatched kernel I can panic the system within 1 minute by doing while (true) do insmod dummy_module.ko; rmmod dummy_module.ko; done and while (true) do cat /proc/modules; done in separate terminals. In the patched kernel I was able to run just over one hour without seeing any issues. I also verified the output of panic via sysrq-c and the output of /proc/modules looks correct for all three states for the dummy_module. dummy_module 12661 0 - Unloading 0xffffffffa03a5000 (OE-) dummy_module 12661 0 - Live 0xffffffffa03bb000 (OE) dummy_module 14015 1 - Loading 0xffffffffa03a5000 (OE+) Signed-off-by: Prarit Bhargava Reviewed-by: Oleg Nesterov Signed-off-by: Rusty Russell Cc: stable@kernel.org