Messages in this thread Patch in this message | | | Date | Thu, 1 Jun 2023 11:12:34 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] sched: Consider task_struct::saved_state in wait_task_inactive(). |
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On Fri, May 26, 2023 at 05:13:35PM +0200, Sebastian Andrzej Siewior wrote: > On 2023-05-26 10:05:43 [+0200], Peter Zijlstra wrote: > > New day, new chances... How's this? Code-gen doesn't look totally > > insane, but then, making sense of an optimizing compiler's output is > > always a wee challenge. > > Noticed it too late but looks good. Tested, works.
Excellent; full patch below. Will go stick in tip/sched/core soonish.
--- Subject: sched: Consider task_struct::saved_state in wait_task_inactive() From: Peter Zijlstra <peterz@infradead.org> Date: Wed May 31 16:39:07 CEST 2023
With the introduction of task_struct::saved_state in commit 5f220be21418 ("sched/wakeup: Prepare for RT sleeping spin/rwlocks") matching the task state has gotten more complicated. That same commit changed try_to_wake_up() to consider both states, but wait_task_inactive() has been neglected.
Sebastian noted that the wait_task_inactive() usage in ptrace_check_attach() can misbehave when ptrace_stop() is blocked on the tasklist_lock after it sets TASK_TRACED.
Therefore extract a common helper from ttwu_state_match() and use that to teach wait_task_inactive() about the PREEMPT_RT locks.
Originally-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- kernel/sched/core.c | 59 ++++++++++++++++++++++++++++++++++++++++++---------- 1 file changed, 48 insertions(+), 11 deletions(-)
--- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3341,6 +3341,39 @@ int migrate_swap(struct task_struct *cur } #endif /* CONFIG_NUMA_BALANCING */ +static __always_inline +int __task_state_match(struct task_struct *p, unsigned int state) +{ + if (READ_ONCE(p->__state) & state) + return 1; + +#ifdef CONFIG_PREEMPT_RT + if (READ_ONCE(p->saved_state) & state) + return -1; +#endif + return 0; +} + +static __always_inline +int task_state_match(struct task_struct *p, unsigned int state) +{ +#ifdef CONFIG_PREEMPT_RT + int match; + + /* + * Serialize against current_save_and_set_rtlock_wait_state() and + * current_restore_rtlock_saved_state(). + */ + raw_spin_lock_irq(&p->pi_lock); + match = __task_state_match(p, state); + raw_spin_unlock_irq(&p->pi_lock); + + return match; +#else + return __task_state_match(p, state); +#endif +} + /* * wait_task_inactive - wait for a thread to unschedule. * @@ -3359,7 +3392,7 @@ int migrate_swap(struct task_struct *cur */ unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state) { - int running, queued; + int running, queued, match; struct rq_flags rf; unsigned long ncsw; struct rq *rq; @@ -3385,7 +3418,7 @@ unsigned long wait_task_inactive(struct * is actually now running somewhere else! */ while (task_on_cpu(rq, p)) { - if (!(READ_ONCE(p->__state) & match_state)) + if (!task_state_match(p, match_state)) return 0; cpu_relax(); } @@ -3400,8 +3433,15 @@ unsigned long wait_task_inactive(struct running = task_on_cpu(rq, p); queued = task_on_rq_queued(p); ncsw = 0; - if (READ_ONCE(p->__state) & match_state) + if ((match = __task_state_match(p, match_state))) { + /* + * When matching on p->saved_state, consider this task + * still queued so it will wait. + */ + if (match < 0) + queued = 1; ncsw = p->nvcsw | LONG_MIN; /* sets MSB */ + } task_rq_unlock(rq, p, &rf); /* @@ -4003,15 +4043,14 @@ static void ttwu_queue(struct task_struc static __always_inline bool ttwu_state_match(struct task_struct *p, unsigned int state, int *success) { + int match; + if (IS_ENABLED(CONFIG_DEBUG_PREEMPT)) { WARN_ON_ONCE((state & TASK_RTLOCK_WAIT) && state != TASK_RTLOCK_WAIT); } - if (READ_ONCE(p->__state) & state) { - *success = 1; - return true; - } + *success = !!(match = __task_state_match(p, state)); #ifdef CONFIG_PREEMPT_RT /* @@ -4027,12 +4066,10 @@ bool ttwu_state_match(struct task_struct * p::saved_state to TASK_RUNNING so any further tests will * not result in false positives vs. @success */ - if (p->saved_state & state) { + if (match < 0) p->saved_state = TASK_RUNNING; - *success = 1; - } #endif - return false; + return match > 0; } /*
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