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Message-ID: <168599258108.404.12910966685801669273.tip-bot2@tip-bot2>
Date: Mon, 05 Jun 2023 19:16:21 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched: Unconditionally use full-fat wait_task_inactive()
The following commit has been merged into the sched/core branch of tip:
Commit-ID: d5e1586617be7093ea3419e3fa9387ed833cdbb1
Gitweb: https://git.kernel.org/tip/d5e1586617be7093ea3419e3fa9387ed833cdbb1
Author: Peter Zijlstra <peterz@...radead.org>
AuthorDate: Fri, 02 Jun 2023 10:42:53 +02:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 05 Jun 2023 21:11:02 +02:00
sched: Unconditionally use full-fat wait_task_inactive()
While modifying wait_task_inactive() for PREEMPT_RT; the build robot
noted that UP got broken. This led to audit and consideration of the
UP implementation of wait_task_inactive().
It looks like the UP implementation is also broken for PREEMPT;
consider task_current_syscall() getting preempted between the two
calls to wait_task_inactive().
Therefore move the wait_task_inactive() implementation out of
CONFIG_SMP and unconditionally use it.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20230602103731.GA630648%40hirez.programming.kicks-ass.net
---
include/linux/sched.h | 7 +-
kernel/sched/core.c | 216 ++++++++++++++++++++---------------------
2 files changed, 110 insertions(+), 113 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index eed5d65..1292d38 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2006,15 +2006,12 @@ static __always_inline void scheduler_ipi(void)
*/
preempt_fold_need_resched();
}
-extern unsigned long wait_task_inactive(struct task_struct *, unsigned int match_state);
#else
static inline void scheduler_ipi(void) { }
-static inline unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state)
-{
- return 1;
-}
#endif
+extern unsigned long wait_task_inactive(struct task_struct *, unsigned int match_state);
+
/*
* Set thread flags in other task's structures.
* See asm/thread_info.h for TIF_xxxx flags available:
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 944c3ae..810cf7d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2213,6 +2213,114 @@ void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
rq_clock_skip_update(rq);
}
+/*
+ * wait_task_inactive - wait for a thread to unschedule.
+ *
+ * Wait for the thread to block in any of the states set in @match_state.
+ * If it changes, i.e. @p might have woken up, then return zero. When we
+ * succeed in waiting for @p to be off its CPU, we return a positive number
+ * (its total switch count). If a second call a short while later returns the
+ * same number, the caller can be sure that @p has remained unscheduled the
+ * whole time.
+ *
+ * The caller must ensure that the task *will* unschedule sometime soon,
+ * else this function might spin for a *long* time. This function can't
+ * be called with interrupts off, or it may introduce deadlock with
+ * smp_call_function() if an IPI is sent by the same process we are
+ * waiting to become inactive.
+ */
+unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state)
+{
+ int running, queued;
+ struct rq_flags rf;
+ unsigned long ncsw;
+ struct rq *rq;
+
+ for (;;) {
+ /*
+ * We do the initial early heuristics without holding
+ * any task-queue locks at all. We'll only try to get
+ * the runqueue lock when things look like they will
+ * work out!
+ */
+ rq = task_rq(p);
+
+ /*
+ * If the task is actively running on another CPU
+ * still, just relax and busy-wait without holding
+ * any locks.
+ *
+ * NOTE! Since we don't hold any locks, it's not
+ * even sure that "rq" stays as the right runqueue!
+ * But we don't care, since "task_on_cpu()" will
+ * return false if the runqueue has changed and p
+ * is actually now running somewhere else!
+ */
+ while (task_on_cpu(rq, p)) {
+ if (!(READ_ONCE(p->__state) & match_state))
+ return 0;
+ cpu_relax();
+ }
+
+ /*
+ * Ok, time to look more closely! We need the rq
+ * lock now, to be *sure*. If we're wrong, we'll
+ * just go back and repeat.
+ */
+ rq = task_rq_lock(p, &rf);
+ trace_sched_wait_task(p);
+ running = task_on_cpu(rq, p);
+ queued = task_on_rq_queued(p);
+ ncsw = 0;
+ if (READ_ONCE(p->__state) & match_state)
+ ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
+ task_rq_unlock(rq, p, &rf);
+
+ /*
+ * If it changed from the expected state, bail out now.
+ */
+ if (unlikely(!ncsw))
+ break;
+
+ /*
+ * Was it really running after all now that we
+ * checked with the proper locks actually held?
+ *
+ * Oops. Go back and try again..
+ */
+ if (unlikely(running)) {
+ cpu_relax();
+ continue;
+ }
+
+ /*
+ * It's not enough that it's not actively running,
+ * it must be off the runqueue _entirely_, and not
+ * preempted!
+ *
+ * So if it was still runnable (but just not actively
+ * running right now), it's preempted, and we should
+ * yield - it could be a while.
+ */
+ if (unlikely(queued)) {
+ ktime_t to = NSEC_PER_SEC / HZ;
+
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ schedule_hrtimeout(&to, HRTIMER_MODE_REL_HARD);
+ continue;
+ }
+
+ /*
+ * Ahh, all good. It wasn't running, and it wasn't
+ * runnable, which means that it will never become
+ * running in the future either. We're all done!
+ */
+ break;
+ }
+
+ return ncsw;
+}
+
#ifdef CONFIG_SMP
static void
@@ -3341,114 +3449,6 @@ out:
}
#endif /* CONFIG_NUMA_BALANCING */
-/*
- * wait_task_inactive - wait for a thread to unschedule.
- *
- * Wait for the thread to block in any of the states set in @match_state.
- * If it changes, i.e. @p might have woken up, then return zero. When we
- * succeed in waiting for @p to be off its CPU, we return a positive number
- * (its total switch count). If a second call a short while later returns the
- * same number, the caller can be sure that @p has remained unscheduled the
- * whole time.
- *
- * The caller must ensure that the task *will* unschedule sometime soon,
- * else this function might spin for a *long* time. This function can't
- * be called with interrupts off, or it may introduce deadlock with
- * smp_call_function() if an IPI is sent by the same process we are
- * waiting to become inactive.
- */
-unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state)
-{
- int running, queued;
- struct rq_flags rf;
- unsigned long ncsw;
- struct rq *rq;
-
- for (;;) {
- /*
- * We do the initial early heuristics without holding
- * any task-queue locks at all. We'll only try to get
- * the runqueue lock when things look like they will
- * work out!
- */
- rq = task_rq(p);
-
- /*
- * If the task is actively running on another CPU
- * still, just relax and busy-wait without holding
- * any locks.
- *
- * NOTE! Since we don't hold any locks, it's not
- * even sure that "rq" stays as the right runqueue!
- * But we don't care, since "task_on_cpu()" will
- * return false if the runqueue has changed and p
- * is actually now running somewhere else!
- */
- while (task_on_cpu(rq, p)) {
- if (!(READ_ONCE(p->__state) & match_state))
- return 0;
- cpu_relax();
- }
-
- /*
- * Ok, time to look more closely! We need the rq
- * lock now, to be *sure*. If we're wrong, we'll
- * just go back and repeat.
- */
- rq = task_rq_lock(p, &rf);
- trace_sched_wait_task(p);
- running = task_on_cpu(rq, p);
- queued = task_on_rq_queued(p);
- ncsw = 0;
- if (READ_ONCE(p->__state) & match_state)
- ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
- task_rq_unlock(rq, p, &rf);
-
- /*
- * If it changed from the expected state, bail out now.
- */
- if (unlikely(!ncsw))
- break;
-
- /*
- * Was it really running after all now that we
- * checked with the proper locks actually held?
- *
- * Oops. Go back and try again..
- */
- if (unlikely(running)) {
- cpu_relax();
- continue;
- }
-
- /*
- * It's not enough that it's not actively running,
- * it must be off the runqueue _entirely_, and not
- * preempted!
- *
- * So if it was still runnable (but just not actively
- * running right now), it's preempted, and we should
- * yield - it could be a while.
- */
- if (unlikely(queued)) {
- ktime_t to = NSEC_PER_SEC / HZ;
-
- set_current_state(TASK_UNINTERRUPTIBLE);
- schedule_hrtimeout(&to, HRTIMER_MODE_REL_HARD);
- continue;
- }
-
- /*
- * Ahh, all good. It wasn't running, and it wasn't
- * runnable, which means that it will never become
- * running in the future either. We're all done!
- */
- break;
- }
-
- return ncsw;
-}
-
/***
* kick_process - kick a running thread to enter/exit the kernel
* @p: the to-be-kicked thread
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