From b3c1d9ec7c59feadd22693f43145d8285bd35b04 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 1 Oct 2018 13:25:32 -0700 Subject: rcu: Avoid double multiply by HZ The rcu_check_gp_start_stall() function multiplies the return value from rcu_jiffies_till_stall_check() by HZ, but the units are already in jiffies. This commit therefore avoids the need for introduction of a jiffies-squared unit by removing the extraneous multiplication. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 121f833acd04..4933f5d9d992 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2603,7 +2603,7 @@ static void force_quiescent_state(void) static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp) { - const unsigned long gpssdelay = rcu_jiffies_till_stall_check() * HZ; + const unsigned long gpssdelay = rcu_jiffies_till_stall_check(); unsigned long flags; unsigned long j; struct rcu_node *rnp_root = rcu_get_root(); -- cgit v1.2.3 From 791416c47153b45f640d52baaf30995d9d396a08 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 1 Oct 2018 15:42:44 -0700 Subject: rcu: Parameterize rcu_check_gp_start_stall() In order to debug forward-progress stalls, it is necessary to check for excessively delayed grace-period starts. This is currently done for RCU CPU stall warnings by rcu_check_gp_start_stall(), which checks to see if the start of a requested grace period has been delayed by an RCU CPU stall warning period. Because rcutorture will need to check for the time consumed by an RCU forward-progress delay, this commit promotes gpssdelay from a local variable to a formal parameter. It is not necessary to export rcu_check_gp_start_stall() because rcutorture will access it via a wrapper function. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 4933f5d9d992..36e30150e1e9 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2600,10 +2600,10 @@ static void force_quiescent_state(void) * This function checks for grace-period requests that fail to motivate * RCU to come out of its idle mode. */ -static void -rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp) +void +rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, + const unsigned long gpssdelay) { - const unsigned long gpssdelay = rcu_jiffies_till_stall_check(); unsigned long flags; unsigned long j; struct rcu_node *rnp_root = rcu_get_root(); @@ -2690,7 +2690,7 @@ static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused local_irq_restore(flags); } - rcu_check_gp_start_stall(rnp, rdp); + rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check()); /* If there are callbacks ready, invoke them. */ if (rcu_segcblist_ready_cbs(&rdp->cblist)) -- cgit v1.2.3 From 691960197e8daa39bf89886ba2e39de1e33f1ce4 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 2 Oct 2018 11:24:08 -0700 Subject: rcu: Add state name to show_rcu_gp_kthreads() output This commit adds the name of the RCU grace-period state to the show_rcu_gp_kthreads() output in order to ease debugging. This commit also moves gp_state_getname() up in the code so that show_rcu_gp_kthreads() can use it. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 25 +++++++++++++------------ 1 file changed, 13 insertions(+), 12 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 36e30150e1e9..ea78532183ac 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -499,6 +499,16 @@ void rcu_force_quiescent_state(void) } EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); +/* + * Convert a ->gp_state value to a character string. + */ +static const char *gp_state_getname(short gs) +{ + if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names)) + return "???"; + return gp_state_names[gs]; +} + /* * Show the state of the grace-period kthreads. */ @@ -508,8 +518,9 @@ void show_rcu_gp_kthreads(void) struct rcu_data *rdp; struct rcu_node *rnp; - pr_info("%s: wait state: %d ->state: %#lx\n", rcu_state.name, - rcu_state.gp_state, rcu_state.gp_kthread->state); + pr_info("%s: wait state: %s(%d) ->state: %#lx\n", rcu_state.name, + gp_state_getname(rcu_state.gp_state), rcu_state.gp_state, + rcu_state.gp_kthread->state); rcu_for_each_node_breadth_first(rnp) { if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed)) continue; @@ -1142,16 +1153,6 @@ static void record_gp_stall_check_time(void) rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs); } -/* - * Convert a ->gp_state value to a character string. - */ -static const char *gp_state_getname(short gs) -{ - if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names)) - return "???"; - return gp_state_names[gs]; -} - /* * Complain about starvation of grace-period kthread. */ -- cgit v1.2.3 From c669c014d1dae9c7cdbfff049c798722f8650829 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 2 Oct 2018 12:42:21 -0700 Subject: rcu: Add jiffies-since-GP-activity to show_rcu_gp_kthreads() This commit adds a printout of the number of jiffies since the last time that the RCU grace-period kthread did any processing. This can be useful when tracking down forward-progress issues. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index ea78532183ac..e7c9848d1e1b 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -515,12 +515,14 @@ static const char *gp_state_getname(short gs) void show_rcu_gp_kthreads(void) { int cpu; + unsigned long j; struct rcu_data *rdp; struct rcu_node *rnp; - pr_info("%s: wait state: %s(%d) ->state: %#lx\n", rcu_state.name, - gp_state_getname(rcu_state.gp_state), rcu_state.gp_state, - rcu_state.gp_kthread->state); + j = jiffies - READ_ONCE(rcu_state.gp_activity); + pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %ld\n", + rcu_state.name, gp_state_getname(rcu_state.gp_state), + rcu_state.gp_state, rcu_state.gp_kthread->state, j); rcu_for_each_node_breadth_first(rnp) { if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed)) continue; -- cgit v1.2.3 From 2320bda26df75c02f86c9fa42c3355ebcd16d8ed Mon Sep 17 00:00:00 2001 From: Zhouyi Zhou Date: Mon, 8 Oct 2018 06:50:41 +0000 Subject: rcu: Adjust the comment of function rcu_is_watching Because RCU avoids interrupting idle CPUs, rcu_is_watching() is used to test whether or not it is currently legal to run RCU read-side critical sections on this CPU. However, the first sentence and last sentences of current comment for rcu_is_watching have opposite meaning of what is expected. This commit therefore fixes this header comment. Signed-off-by: Zhouyi Zhou Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e7c9848d1e1b..429a46fb087a 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -904,12 +904,12 @@ void rcu_irq_enter_irqson(void) } /** - * rcu_is_watching - see if RCU thinks that the current CPU is idle + * rcu_is_watching - see if RCU thinks that the current CPU is not idle * * Return true if RCU is watching the running CPU, which means that this * CPU can safely enter RCU read-side critical sections. In other words, - * if the current CPU is in its idle loop and is neither in an interrupt - * or NMI handler, return true. + * if the current CPU is not in its idle loop or is in an interrupt or + * NMI handler, return true. */ bool notrace rcu_is_watching(void) { -- cgit v1.2.3 From 0a89e5a402e957a97129423599a6ef6342da2764 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 15 Oct 2018 10:00:58 -0700 Subject: rcu: Trace end of grace period before end of grace period Currently, rcu_gp_cleanup() traces the end of the old grace period after the old grace period has officially ended. This might make intuitive sense, but it also makes for confusing event-trace output because the "end" trace displays not the old but instead the new grace-period number. This commit therefore traces the end of an old grace period just before that grace period officially ends. Reported-by: Aravinda Prasad Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 429a46fb087a..61bae41b1afe 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2035,9 +2035,9 @@ static void rcu_gp_cleanup(void) rnp = rcu_get_root(); raw_spin_lock_irq_rcu_node(rnp); /* GP before ->gp_seq update. */ - /* Declare grace period done. */ - rcu_seq_end(&rcu_state.gp_seq); + /* Declare grace period done, trace first to use old GP number. */ trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end")); + rcu_seq_end(&rcu_state.gp_seq); rcu_state.gp_state = RCU_GP_IDLE; /* Check for GP requests since above loop. */ rdp = this_cpu_ptr(&rcu_data); -- cgit v1.2.3