From: "Paul E. McKenney" paulmck@kernel.org

mainline inclusion from mainline-v5.12-rc1 commit 243027a3c80564bf96e40437ffac46efb9f5f2b5 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I7OIXK

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

--------------------------------

When the RCU CPU stall-warning code detects that the RCU grace-period kthread is being starved, it dumps that kthread's stack. This can sometimes be useful, but it is also useful to know what is running on the CPU that this kthread is attempting to run on. This commit therefore adds a stack trace of this CPU in order to help track down whatever it is that might be preventing RCU's grace-period kthread from running.

Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Zhen Lei thunder.leizhen@huawei.com --- kernel/rcu/tree_stall.h | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 251a9af3709afd6..5df4640254ace16 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -449,20 +449,27 @@ static void print_cpu_stall_info(int cpu) /* Complain about starvation of grace-period kthread. */ static void rcu_check_gp_kthread_starvation(void) { + int cpu; struct task_struct *gpk = rcu_state.gp_kthread; unsigned long j;

if (rcu_is_gp_kthread_starving(&j)) { + cpu = gpk ? task_cpu(gpk) : -1; pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n", rcu_state.name, j, (long)rcu_seq_current(&rcu_state.gp_seq), data_race(rcu_state.gp_flags), gp_state_getname(rcu_state.gp_state), rcu_state.gp_state, - gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1); + gpk ? gpk->state : ~0, cpu); if (gpk) { pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name); pr_err("RCU grace-period kthread stack dump:\n"); sched_show_task(gpk); + if (cpu >= 0) { + pr_err("Stack dump where RCU grace-period kthread last ran:\n"); + if (!trigger_single_cpu_backtrace(cpu)) + dump_cpu_task(cpu); + } wake_up_process(gpk); } }

From: Neeraj Upadhyay neeraju@codeaurora.org

mainline inclusion from mainline-v5.12-rc1 commit 683954e55c981467bfd4688417e914bafc40959f category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I7OIXK

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

--------------------------------

For a new grace period request, the RCU GP kthread transitions through following states:

a. [RCU_GP_WAIT_GPS] -> [RCU_GP_DONE_GPS]

The RCU_GP_WAIT_GPS state is where the GP kthread waits for a request for a new GP. Once it receives a request (for example, when a new RCU callback is queued), the GP kthread transitions to RCU_GP_DONE_GPS.

b. [RCU_GP_DONE_GPS] -> [RCU_GP_ONOFF]

Grace period initialization starts in rcu_gp_init(), which records the start of new GP in rcu_state.gp_seq and transitions to RCU_GP_ONOFF.

c. [RCU_GP_ONOFF] -> [RCU_GP_INIT]

The purpose of the RCU_GP_ONOFF state is to apply the online/offline information that was buffered for any CPUs that recently came online or went offline. This state is maintained in per-leaf rcu_node bitmasks, with the buffered state in ->qsmaskinitnext and the state for the upcoming GP in ->qsmaskinit. At the end of this RCU_GP_ONOFF state, each bit in ->qsmaskinit will correspond to a CPU that must pass through a quiescent state before the upcoming grace period is allowed to complete.

However, a leaf rcu_node structure with an all-zeroes ->qsmaskinit cannot necessarily be ignored. In preemptible RCU, there might well be tasks still in RCU read-side critical sections that were first preempted while running on one of the CPUs managed by this structure. Such tasks will be queued on this structure's ->blkd_tasks list. Only after this list fully drains can this leaf rcu_node structure be ignored, and even then only if none of its CPUs have come back online in the meantime. Once that happens, the ->qsmaskinit masks further up the tree will be updated to exclude this leaf rcu_node structure.

Once the ->qsmaskinitnext and ->qsmaskinit fields have been updated as needed, the GP kthread transitions to RCU_GP_INIT.

d. [RCU_GP_INIT] -> [RCU_GP_WAIT_FQS]

The purpose of the RCU_GP_INIT state is to copy each ->qsmaskinit to the ->qsmask field within each rcu_node structure. This copying is done breadth-first from the root to the leaves. Why not just copy directly from ->qsmaskinitnext to ->qsmask? Because the ->qsmaskinitnext masks can change in the meantime as additional CPUs come online or go offline. Such changes would result in inconsistencies in the ->qsmask fields up and down the tree, which could in turn result in too-short grace periods or grace-period hangs. These issues are avoided by snapshotting the leaf rcu_node structures' ->qsmaskinitnext fields into their ->qsmaskinit counterparts, generating a consistent set of ->qsmaskinit fields throughout the tree, and only then copying these consistent ->qsmaskinit fields to their ->qsmask counterparts.

Once this initialization step is complete, the GP kthread transitions to RCU_GP_WAIT_FQS, where it waits to do a force-quiescent-state scan on the one hand or for the end of the grace period on the other.

e. [RCU_GP_WAIT_FQS] -> [RCU_GP_DOING_FQS]

The RCU_GP_WAIT_FQS state waits for one of three things: (1) An explicit request to do a force-quiescent-state scan, (2) The end of the grace period, or (3) A short interval of time, after which it will do a force-quiescent-state (FQS) scan. The explicit request can come from rcutorture or from any CPU that has too many RCU callbacks queued (see the qhimark kernel parameter and the RCU_GP_FLAG_OVLD flag). The aforementioned "short period of time" is specified by the jiffies_till_first_fqs boot parameter for a given grace period's first FQS scan and by the jiffies_till_next_fqs for later FQS scans.

Either way, once the wait is over, the GP kthread transitions to RCU_GP_DOING_FQS.

f. [RCU_GP_DOING_FQS] -> [RCU_GP_CLEANUP]

The RCU_GP_DOING_FQS state performs an FQS scan. Each such scan carries out two functions for any CPU whose bit is still set in its leaf rcu_node structure's ->qsmask field, that is, for any CPU that has not yet reported a quiescent state for the current grace period:

i. Report quiescent states on behalf of CPUs that have been observed to be idle (from an RCU perspective) since the beginning of the grace period.

ii. If the current grace period is too old, take various actions to encourage holdout CPUs to pass through quiescent states, including enlisting the aid of any calls to cond_resched() and might_sleep(), and even including IPIing the holdout CPUs.

These checks are skipped for any leaf rcu_node structure with a all-zero ->qsmask field, however such structures are subject to RCU priority boosting if there are tasks on a given structure blocking the current grace period. The end of the grace period is detected when the root rcu_node structure's ->qsmask is zero and when there are no longer any preempted tasks blocking the current grace period. (No, this last check is not redundant. To see this, consider an rcu_node tree having exactly one structure that serves as both root and leaf.)

Once the end of the grace period is detected, the GP kthread transitions to RCU_GP_CLEANUP.

g. [RCU_GP_CLEANUP] -> [RCU_GP_CLEANED]

The RCU_GP_CLEANUP state marks the end of grace period by updating the rcu_state structure's ->gp_seq field and also all rcu_node structures' ->gp_seq field. As before, the rcu_node tree is traversed in breadth first order. Once this update is complete, the GP kthread transitions to the RCU_GP_CLEANED state.

i. [RCU_GP_CLEANED] -> [RCU_GP_INIT]

Once in the RCU_GP_CLEANED state, the GP kthread immediately transitions into the RCU_GP_INIT state.

j. The role of timers.

If there is at least one idle CPU, and if timers are not firing, the transition from RCU_GP_DOING_FQS to RCU_GP_CLEANUP will never happen. Timers can fail to fire for a number of reasons, including issues in timer configuration, issues in the timer framework, and failure to handle softirqs (for example, when there is a storm of interrupts). Whatever the reason, if the timers fail to fire, the GP kthread will never be awakened, resulting in RCU CPU stall warnings and eventually in OOM.

However, an RCU CPU stall warning has a large number of potential causes, as documented in Documentation/RCU/stallwarn.rst. This commit therefore adds analysis to the RCU CPU stall-warning code to emit an additional message if the cause of the stall is likely to be timer failure.

Signed-off-by: Neeraj Upadhyay neeraju@codeaurora.org Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Zhen Lei thunder.leizhen@huawei.com --- Documentation/RCU/stallwarn.rst | 23 ++++++++++++++++++++++- kernel/rcu/tree.c | 25 +++++++++++++++---------- kernel/rcu/tree_stall.h | 32 ++++++++++++++++++++++++++++++++ 3 files changed, 69 insertions(+), 11 deletions(-)

diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst index c9ab6af4d3be9a0..d53856cc639089d 100644 --- a/Documentation/RCU/stallwarn.rst +++ b/Documentation/RCU/stallwarn.rst @@ -92,7 +92,9 @@ warnings: buggy timer hardware through bugs in the interrupt or exception path (whether hardware, firmware, or software) through bugs in Linux's timer subsystem through bugs in the scheduler, and, - yes, even including bugs in RCU itself. + yes, even including bugs in RCU itself. It can also result in + the ``rcu_.*timer wakeup didn't happen for`` console-log message, + which will include additional debugging information.

- A bug in the RCU implementation.

@@ -292,6 +294,25 @@ kthread is waiting for a short timeout, the "state" precedes value of the task_struct ->state field, and the "cpu" indicates that the grace-period kthread last ran on CPU 5.

+If the relevant grace-period kthread does not wake from FQS wait in a +reasonable time, then the following additional line is printed:: + + kthread timer wakeup didn't happen for 23804 jiffies! g7076 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 + +The "23804" indicates that kthread's timer expired more than 23 thousand +jiffies ago. The rest of the line has meaning similar to the kthread +starvation case. + +Additionally, the following line is printed:: + + Possible timer handling issue on cpu=4 timer-softirq=11142 + +Here "cpu" indicates that the grace-period kthread last ran on CPU 4, +where it queued the fqs timer. The number following the "timer-softirq" +is the current ``TIMER_SOFTIRQ`` count on cpu 4. If this value does not +change on successive RCU CPU stall warnings, there is further reason to +suspect a timer problem. +

Multiple Warnings From One Stall ================================ diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e1bbde2648e2eaf..77b4e1c642941b5 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1787,7 +1787,7 @@ static bool rcu_gp_init(void) * go offline later. Please also refer to "Hotplug CPU" section * of RCU's Requirements documentation. */ - rcu_state.gp_state = RCU_GP_ONOFF; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_ONOFF); rcu_for_each_leaf_node(rnp) { smp_mb(); // Pair with barriers used when updating ->ofl_seq to odd values. firstseq = READ_ONCE(rnp->ofl_seq); @@ -1853,7 +1853,7 @@ static bool rcu_gp_init(void) * The grace period cannot complete until the initialization * process finishes, because this kthread handles both. */ - rcu_state.gp_state = RCU_GP_INIT; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_INIT); rcu_for_each_node_breadth_first(rnp) { rcu_gp_slow(gp_init_delay); raw_spin_lock_irqsave_rcu_node(rnp, flags); @@ -1952,17 +1952,22 @@ static void rcu_gp_fqs_loop(void) ret = 0; for (;;) { if (!ret) { - rcu_state.jiffies_force_qs = jiffies + j; + WRITE_ONCE(rcu_state.jiffies_force_qs, jiffies + j); + /* + * jiffies_force_qs before RCU_GP_WAIT_FQS state + * update; required for stall checks. + */ + smp_wmb(); WRITE_ONCE(rcu_state.jiffies_kick_kthreads, jiffies + (j ? 3 * j : 2)); } trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("fqswait")); - rcu_state.gp_state = RCU_GP_WAIT_FQS; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_FQS); ret = swait_event_idle_timeout_exclusive( rcu_state.gp_wq, rcu_gp_fqs_check_wake(&gf), j); rcu_gp_torture_wait(); - rcu_state.gp_state = RCU_GP_DOING_FQS; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS); /* Locking provides needed memory barriers. */ /* If grace period done, leave loop. */ if (!READ_ONCE(rnp->qsmask) && @@ -2076,7 +2081,7 @@ static void rcu_gp_cleanup(void) trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end")); rcu_seq_end(&rcu_state.gp_seq); ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq); - rcu_state.gp_state = RCU_GP_IDLE; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_IDLE); /* Check for GP requests since above loop. */ rdp = this_cpu_ptr(&rcu_data); if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) { @@ -2116,12 +2121,12 @@ static int __noreturn rcu_gp_kthread(void *unused) for (;;) { trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("reqwait")); - rcu_state.gp_state = RCU_GP_WAIT_GPS; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_GPS); swait_event_idle_exclusive(rcu_state.gp_wq, READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_INIT); rcu_gp_torture_wait(); - rcu_state.gp_state = RCU_GP_DONE_GPS; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_DONE_GPS); /* Locking provides needed memory barrier. */ if (rcu_gp_init()) break; @@ -2136,9 +2141,9 @@ static int __noreturn rcu_gp_kthread(void *unused) rcu_gp_fqs_loop();

/* Handle grace-period end. */ - rcu_state.gp_state = RCU_GP_CLEANUP; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANUP); rcu_gp_cleanup(); - rcu_state.gp_state = RCU_GP_CLEANED; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANED); } }

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index c38622ff72673ef..f7d031ef559395f 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -482,6 +482,36 @@ static void rcu_check_gp_kthread_starvation(void) } }

+/* Complain about missing wakeups from expired fqs wait timer */ +static void rcu_check_gp_kthread_expired_fqs_timer(void) +{ + struct task_struct *gpk = rcu_state.gp_kthread; + short gp_state; + unsigned long jiffies_fqs; + int cpu; + + /* + * Order reads of .gp_state and .jiffies_force_qs. + * Matching smp_wmb() is present in rcu_gp_fqs_loop(). + */ + gp_state = smp_load_acquire(&rcu_state.gp_state); + jiffies_fqs = READ_ONCE(rcu_state.jiffies_force_qs); + + if (gp_state == RCU_GP_WAIT_FQS && + time_after(jiffies, jiffies_fqs + RCU_STALL_MIGHT_MIN) && + gpk && !READ_ONCE(gpk->on_rq)) { + cpu = task_cpu(gpk); + pr_err("%s kthread timer wakeup didn't happen for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx\n", + rcu_state.name, (jiffies - jiffies_fqs), + (long)rcu_seq_current(&rcu_state.gp_seq), + data_race(rcu_state.gp_flags), + gp_state_getname(RCU_GP_WAIT_FQS), RCU_GP_WAIT_FQS, + gpk->state); + pr_err("\tPossible timer handling issue on cpu=%d timer-softirq=%u\n", + cpu, kstat_softirqs_cpu(TIMER_SOFTIRQ, cpu)); + } +} + static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) { int cpu; @@ -546,6 +576,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) WRITE_ONCE(rcu_state.jiffies_stall, jiffies + 3 * rcu_jiffies_till_stall_check() + 3);

+ rcu_check_gp_kthread_expired_fqs_timer(); rcu_check_gp_kthread_starvation();

panic_on_rcu_stall(); @@ -583,6 +614,7 @@ static void print_cpu_stall(unsigned long gps) jiffies - gps, (long)rcu_seq_current(&rcu_state.gp_seq), totqlen);

+ rcu_check_gp_kthread_expired_fqs_timer(); rcu_check_gp_kthread_starvation();

rcu_dump_cpu_stacks();

mainline inclusion from mainline-v6.1-rc1 commit bc1cca97e6da6c7c34db7c5b864bb354ca5305ac category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I7OIXK

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

--------------------------------

The dump_cpu_task() function does not print registers on architectures that do not support NMIs. However, registers can be useful for debugging. Fortunately, in the case where dump_cpu_task() is invoked from an interrupt handler and is dumping the current CPU's stack, the get_irq_regs() function can be used to get the registers.

Therefore, this commit makes dump_cpu_task() check to see if it is being asked to dump the current CPU's stack from within an interrupt handler, and, if so, it uses the get_irq_regs() function to obtain the registers. On systems that do support NMIs, this commit has the further advantage of avoiding a self-NMI in this case.

This is an example of rcu self-detected stall on arm64, which does not support NMIs: [ 27.501721] rcu: INFO: rcu_preempt self-detected stall on CPU [ 27.502238] rcu: 0-....: (1250 ticks this GP) idle=4f7/1/0x4000000000000000 softirq=2594/2594 fqs=619 [ 27.502632] (t=1251 jiffies g=2989 q=29 ncpus=4) [ 27.503845] CPU: 0 PID: 306 Comm: test0 Not tainted 5.19.0-rc7-00009-g1c1a6c29ff99-dirty #46 [ 27.504732] Hardware name: linux,dummy-virt (DT) [ 27.504947] pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 27.504998] pc : arch_counter_read+0x18/0x24 [ 27.505301] lr : arch_counter_read+0x18/0x24 [ 27.505328] sp : ffff80000b29bdf0 [ 27.505345] x29: ffff80000b29bdf0 x28: 0000000000000000 x27: 0000000000000000 [ 27.505475] x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000 [ 27.505553] x23: 0000000000001f40 x22: ffff800009849c48 x21: 000000065f871ae0 [ 27.505627] x20: 00000000000025ec x19: ffff80000a6eb300 x18: ffffffffffffffff [ 27.505654] x17: 0000000000000001 x16: 0000000000000000 x15: ffff80000a6d0296 [ 27.505681] x14: ffffffffffffffff x13: ffff80000a29bc18 x12: 0000000000000426 [ 27.505709] x11: 0000000000000162 x10: ffff80000a2f3c18 x9 : ffff80000a29bc18 [ 27.505736] x8 : 00000000ffffefff x7 : ffff80000a2f3c18 x6 : 00000000759bd013 [ 27.505761] x5 : 01ffffffffffffff x4 : 0002dc6c00000000 x3 : 0000000000000017 [ 27.505787] x2 : 00000000000025ec x1 : ffff80000b29bdf0 x0 : 0000000075a30653 [ 27.505937] Call trace: [ 27.506002] arch_counter_read+0x18/0x24 [ 27.506171] ktime_get+0x48/0xa0 [ 27.506207] test_task+0x70/0xf0 [ 27.506227] kthread+0x10c/0x110 [ 27.506243] ret_from_fork+0x10/0x20

This is a marked improvement over the old output: [ 27.944550] rcu: INFO: rcu_preempt self-detected stall on CPU [ 27.944980] rcu: 0-....: (1249 ticks this GP) idle=cbb/1/0x4000000000000000 softirq=2610/2610 fqs=614 [ 27.945407] (t=1251 jiffies g=2681 q=28 ncpus=4) [ 27.945731] Task dump for CPU 0: [ 27.945844] task:test0 state:R running task stack: 0 pid: 306 ppid: 2 flags:0x0000000a [ 27.946073] Call trace: [ 27.946151] dump_backtrace.part.0+0xc8/0xd4 [ 27.946378] show_stack+0x18/0x70 [ 27.946405] sched_show_task+0x150/0x180 [ 27.946427] dump_cpu_task+0x44/0x54 [ 27.947193] rcu_dump_cpu_stacks+0xec/0x130 [ 27.947212] rcu_sched_clock_irq+0xb18/0xef0 [ 27.947231] update_process_times+0x68/0xac [ 27.947248] tick_sched_handle+0x34/0x60 [ 27.947266] tick_sched_timer+0x4c/0xa4 [ 27.947281] __hrtimer_run_queues+0x178/0x360 [ 27.947295] hrtimer_interrupt+0xe8/0x244 [ 27.947309] arch_timer_handler_virt+0x38/0x4c [ 27.947326] handle_percpu_devid_irq+0x88/0x230 [ 27.947342] generic_handle_domain_irq+0x2c/0x44 [ 27.947357] gic_handle_irq+0x44/0xc4 [ 27.947376] call_on_irq_stack+0x2c/0x54 [ 27.947415] do_interrupt_handler+0x80/0x94 [ 27.947431] el1_interrupt+0x34/0x70 [ 27.947447] el1h_64_irq_handler+0x18/0x24 [ 27.947462] el1h_64_irq+0x64/0x68 <--- the above backtrace is worthless [ 27.947474] arch_counter_read+0x18/0x24 [ 27.947487] ktime_get+0x48/0xa0 [ 27.947501] test_task+0x70/0xf0 [ 27.947520] kthread+0x10c/0x110 [ 27.947538] ret_from_fork+0x10/0x20

Signed-off-by: Zhen Lei thunder.leizhen@huawei.com Signed-off-by: Paul E. McKenney paulmck@kernel.org Cc: Ingo Molnar mingo@redhat.com Cc: Peter Zijlstra peterz@infradead.org Cc: Juri Lelli juri.lelli@redhat.com Cc: Vincent Guittot vincent.guittot@linaro.org Cc: Dietmar Eggemann dietmar.eggemann@arm.com Cc: Ben Segall bsegall@google.com Cc: Mel Gorman mgorman@suse.de Cc: Daniel Bristot de Oliveira bristot@redhat.com Cc: Valentin Schneider vschneid@redhat.com Conflicts: kernel/sched/core.c

Signed-off-by: Zhen Lei thunder.leizhen@huawei.com --- kernel/sched/core.c | 11 +++++++++++ 1 file changed, 11 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c index ce21533fa5d32e2..d026b22838eb531 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -17,6 +17,7 @@ #include <linux/kcov.h> #include <linux/scs.h>

+#include <asm/irq_regs.h> #include <asm/switch_to.h> #include <asm/tlb.h>

@@ -10052,6 +10053,16 @@ struct cgroup_subsys cpu_cgrp_subsys = {

void dump_cpu_task(int cpu) { + if (cpu == smp_processor_id() && in_irq()) { + struct pt_regs *regs; + + regs = get_irq_regs(); + if (regs) { + show_regs(regs); + return; + } + } + if (trigger_single_cpu_backtrace(cpu)) return;

mainline inclusion from mainline-v6.3-rc1 commit 7c182722a0a9447e31f9645de4f311e5bc59b480 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I7OIXK

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

--------------------------------

Add a function nr_context_switches_cpu() that returns number of context switches since boot on the specified CPU. This information will be used to diagnose RCU CPU stalls.

Signed-off-by: Zhen Lei thunder.leizhen@huawei.com Cc: Ingo Molnar mingo@redhat.com Cc: Peter Zijlstra peterz@infradead.org Cc: Juri Lelli juri.lelli@redhat.com Cc: Vincent Guittot vincent.guittot@linaro.org Cc: Dietmar Eggemann dietmar.eggemann@arm.com Cc: Steven Rostedt rostedt@goodmis.org Cc: Ben Segall bsegall@google.com Cc: Mel Gorman mgorman@suse.de Cc: Daniel Bristot de Oliveira bristot@redhat.com Cc: Valentin Schneider vschneid@redhat.com Reviewed-by: Frederic Weisbecker frederic@kernel.org Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Zhen Lei thunder.leizhen@huawei.com --- include/linux/kernel_stat.h | 1 + kernel/sched/core.c | 5 +++++ 2 files changed, 6 insertions(+)

diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h index 72b90b35e9e250a..c0f7e283cf97329 100644 --- a/include/linux/kernel_stat.h +++ b/include/linux/kernel_stat.h @@ -49,6 +49,7 @@ DECLARE_PER_CPU(struct kernel_cpustat, kernel_cpustat); #define kstat_cpu(cpu) per_cpu(kstat, cpu) #define kcpustat_cpu(cpu) per_cpu(kernel_cpustat, cpu)

+extern unsigned long long nr_context_switches_cpu(int cpu); extern unsigned long long nr_context_switches(void);

extern unsigned int kstat_irqs_cpu(unsigned int irq, int cpu); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index d026b22838eb531..0ed931ba173847d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4267,6 +4267,11 @@ bool single_task_running(void) } EXPORT_SYMBOL(single_task_running);

+unsigned long long nr_context_switches_cpu(int cpu) +{ + return cpu_rq(cpu)->nr_switches; +} + unsigned long long nr_context_switches(void) { int i;

mainline inclusion from mainline-v6.3-rc1 commit 3ab955de929a53245c89deb7ff9992b6eebbe4e8 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I7OIXK

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

--------------------------------

Time stamps are added to the output in kernels built with CONFIG_PRINTK_TIME=y, which causes misaligned output. Therefore, replace pr_cont() with pr_err(), which fixes alignment and gets rid of a couple of despised pr_cont() calls.

Before: [ 37.567343] rcu: INFO: rcu_preempt self-detected stall on CPU [ 37.567839] rcu: 0-....: (1500 ticks this GP) idle=*** [ 37.568270] (t=1501 jiffies g=4717 q=28 ncpus=4) [ 37.568668] CPU: 0 PID: 313 Comm: test0 Not tainted 6.1.0-rc4 #8

After: [ 36.762074] rcu: INFO: rcu_preempt self-detected stall on CPU [ 36.762543] rcu: 0-....: (1499 ticks this GP) idle=*** [ 36.763003] rcu: (t=1500 jiffies g=5097 q=27 ncpus=4) [ 36.763522] CPU: 0 PID: 313 Comm: test0 Not tainted 6.1.0-rc4 #9

Signed-off-by: Zhen Lei thunder.leizhen@huawei.com Reviewed-by: Frederic Weisbecker frederic@kernel.org Signed-off-by: Paul E. McKenney paulmck@kernel.org Conflicts: kernel/rcu/tree_stall.h

Signed-off-by: Zhen Lei thunder.leizhen@huawei.com --- kernel/rcu/tree_stall.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 945b7de36a76d6d..e9d8b6dbde7c458 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -580,7 +580,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)

for_each_possible_cpu(cpu) totqlen += rcu_get_n_cbs_cpu(cpu); - pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n", + pr_err("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n", smp_processor_id(), (long)(jiffies - gps), (long)rcu_seq_current(&rcu_state.gp_seq), totqlen); if (ndetected) { @@ -640,7 +640,7 @@ static void print_cpu_stall(unsigned long gps) raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags); for_each_possible_cpu(cpu) totqlen += rcu_get_n_cbs_cpu(cpu); - pr_cont("\t(t=%lu jiffies g=%ld q=%lu)\n", + pr_err("\t(t=%lu jiffies g=%ld q=%lu)\n", jiffies - gps, (long)rcu_seq_current(&rcu_state.gp_seq), totqlen);