6.12-stable review patch. If anyone has any objections, please let me know.
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From: Chengming Zhou chengming.zhou@linux.dev
[ Upstream commit 7d9da040575b343085287686fa902a5b2d43c7ca ]
When running hackbench in a cgroup with bandwidth throttling enabled, following PSI splat was observed:
psi: inconsistent task state! task=1831:hackbench cpu=8 psi_flags=14 clear=0 set=4
When investigating the series of events leading up to the splat, following sequence was observed:
[008] d..2.: sched_switch: ... ==> next_comm=hackbench next_pid=1831 next_prio=120 ... [008] dN.2.: dequeue_entity(task delayed): task=hackbench pid=1831 cfs_rq->throttled=0 [008] dN.2.: pick_task_fair: check_cfs_rq_runtime() throttled cfs_rq on CPU8 # CPU8 goes into newidle balance and releases the rq lock ... # CPU15 on same LLC Domain is trying to wakeup hackbench(pid=1831) [015] d..4.: psi_flags_change: psi: task state: task=1831:hackbench cpu=8 psi_flags=14 clear=0 set=4 final=14 # Splat (cfs_rq->throttled=1) [015] d..4.: sched_wakeup: comm=hackbench pid=1831 prio=120 target_cpu=008 # Task has woken on a throttled hierarchy [008] d..2.: sched_switch: prev_comm=hackbench prev_pid=1831 prev_prio=120 prev_state=S ==> ...
psi_dequeue() relies on psi_sched_switch() to set the correct PSI flags for the blocked entity, however, with the introduction of DELAY_DEQUEUE, the block task can wakeup when newidle balance drops the runqueue lock during __schedule().
If a task wakes before psi_sched_switch() adjusts the PSI flags, skip any modifications in psi_enqueue() which would still see the flags of a running task and not a blocked one. Instead, rely on psi_sched_switch() to do the right thing.
Since the status returned by try_to_block_task() may no longer be true by the time schedule reaches psi_sched_switch(), check if the task is blocked or not using a combination of task_on_rq_queued() and p->se.sched_delayed checks.
[ prateek: Commit message, testing, early bailout in psi_enqueue() ]
Fixes: 152e11f6df29 ("sched/fair: Implement delayed dequeue") # 1a6151017ee5 Signed-off-by: Chengming Zhou chengming.zhou@linux.dev Signed-off-by: K Prateek Nayak kprateek.nayak@amd.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Chengming Zhou chengming.zhou@linux.dev Link: https://lore.kernel.org/r/20241227061941.2315-1-kprateek.nayak@amd.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/core.c | 6 +++--- kernel/sched/stats.h | 4 ++++ 2 files changed, 7 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index c1d2d46feec50..aba41c69f09c4 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6593,7 +6593,6 @@ static void __sched notrace __schedule(int sched_mode) * as a preemption by schedule_debug() and RCU. */ bool preempt = sched_mode > SM_NONE; - bool block = false; unsigned long *switch_count; unsigned long prev_state; struct rq_flags rf; @@ -6654,7 +6653,7 @@ static void __sched notrace __schedule(int sched_mode) goto picked; } } else if (!preempt && prev_state) { - block = try_to_block_task(rq, prev, prev_state); + try_to_block_task(rq, prev, prev_state); switch_count = &prev->nvcsw; }
@@ -6699,7 +6698,8 @@ static void __sched notrace __schedule(int sched_mode)
migrate_disable_switch(rq, prev); psi_account_irqtime(rq, prev, next); - psi_sched_switch(prev, next, block); + psi_sched_switch(prev, next, !task_on_rq_queued(prev) || + prev->se.sched_delayed);
trace_sched_switch(preempt, prev, next, prev_state);
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h index 8ee0add5a48a8..6ade91bce63ee 100644 --- a/kernel/sched/stats.h +++ b/kernel/sched/stats.h @@ -138,6 +138,10 @@ static inline void psi_enqueue(struct task_struct *p, int flags) if (flags & ENQUEUE_RESTORE) return;
+ /* psi_sched_switch() will handle the flags */ + if (task_on_cpu(task_rq(p), p)) + return; + if (p->se.sched_delayed) { /* CPU migration of "sleeping" task */ SCHED_WARN_ON(!(flags & ENQUEUE_MIGRATED));