[PATCH 6/7] sched: Simplify set_affinity_pending refcounts
From: Paul Gortmaker <hidden>
Date: 2021-06-08 04:38:48
Subsystem:
scheduler, the rest · Maintainers:
Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot, Linus Torvalds
From: Peter Zijlstra <peterz@infradead.org>
commit 50caf9c14b1498c90cf808dbba2ca29bd32ccba4 upstream.
Now that we have set_affinity_pending::stop_pending to indicate if a
stopper is in progress, and we have the guarantee that if that stopper
exists, it will (eventually) complete our @pending we can simplify the
refcount scheme by no longer counting the stopper thread.
Fixes: 6d337eab041d ("sched: Fix migrate_disable() vs set_cpus_allowed_ptr()")
Cc: stable@kernel.org
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Valentin Schneider <redacted>
Link: https://lkml.kernel.org/r/20210224131355.724130207@infradead.org
Signed-off-by: Paul Gortmaker <redacted>
---
kernel/sched/core.c | 32 ++++++++++++++++++++------------
1 file changed, 20 insertions(+), 12 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 20588a59300d..35d8b80d7cb8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c@@ -1898,6 +1898,10 @@ struct migration_arg { struct set_affinity_pending *pending; }; +/* + * @refs: number of wait_for_completion() + * @stop_pending: is @stop_work in use + */ struct set_affinity_pending { refcount_t refs; unsigned int stop_pending;
@@ -2033,10 +2037,6 @@ static int migration_cpu_stop(void *data) if (complete) complete_all(&pending->done); - /* For pending->{arg,stop_work} */ - if (pending && refcount_dec_and_test(&pending->refs)) - wake_up_var(&pending->refs); - return 0; }
@@ -2235,12 +2235,16 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag push_task = get_task_struct(p); } + /* + * If there are pending waiters, but no pending stop_work, + * then complete now. + */ pending = p->migration_pending; - if (pending) { - refcount_inc(&pending->refs); + if (pending && !pending->stop_pending) { p->migration_pending = NULL; complete = true; } + task_rq_unlock(rq, p, rf); if (push_task) {
@@ -2249,7 +2253,7 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag } if (complete) - goto do_complete; + complete_all(&pending->done); return 0; }
@@ -2300,9 +2304,9 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag if (!stop_pending) pending->stop_pending = true; - refcount_inc(&pending->refs); /* pending->{arg,stop_work} */ if (flags & SCA_MIGRATE_ENABLE) p->migration_flags &= ~MDF_PUSH; + task_rq_unlock(rq, p, rf); if (!stop_pending) {
@@ -2318,12 +2322,13 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag if (task_on_rq_queued(p)) rq = move_queued_task(rq, rf, p, dest_cpu); - p->migration_pending = NULL; - complete = true; + if (!pending->stop_pending) { + p->migration_pending = NULL; + complete = true; + } } task_rq_unlock(rq, p, rf); -do_complete: if (complete) complete_all(&pending->done); }
@@ -2331,7 +2336,7 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag wait_for_completion(&pending->done); if (refcount_dec_and_test(&pending->refs)) - wake_up_var(&pending->refs); + wake_up_var(&pending->refs); /* No UaF, just an address */ /* * Block the original owner of &pending until all subsequent callers
@@ -2339,6 +2344,9 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag */ wait_var_event(&my_pending.refs, !refcount_read(&my_pending.refs)); + /* ARGH */ + WARN_ON_ONCE(my_pending.stop_pending); + return 0; }
--
2.25.1