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sched: Simplify set_affinity_pending refcounts

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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: 6d337eab04 ("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 <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/20210224131355.724130207@infradead.org
This commit is contained in:
Peter Zijlstra 2021-02-24 11:42:08 +01:00 • committed by Ingo Molnar
parent 9e81889c76
commit 50caf9c14b
1 changed files with 20 additions and 12 deletions
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32
kernel/sched/core.c
View file

@ -1862,6 +1862,10 @@ struct migration_arg {
struct set_affinity_pending *pending; struct set_affinity_pending *pending;
}; };
/*
* @refs: number of wait_for_completion()
* @stop_pending: is @stop_work in use
*/
struct set_affinity_pending { struct set_affinity_pending {
refcount_t refs; refcount_t refs;
unsigned int stop_pending; unsigned int stop_pending;
@ -1997,10 +2001,6 @@ out:
if (complete) if (complete)
complete_all(&pending->done); complete_all(&pending->done);
/* For pending->{arg,stop_work} */
if (pending && refcount_dec_and_test(&pending->refs))
wake_up_var(&pending->refs);
return 0; return 0;
} }
@ -2199,12 +2199,16 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag
push_task = get_task_struct(p); push_task = get_task_struct(p);
} }
/*
* If there are pending waiters, but no pending stop_work,
* then complete now.
*/
pending = p->migration_pending; pending = p->migration_pending;
if (pending) { if (pending && !pending->stop_pending) {
refcount_inc(&pending->refs);
p->migration_pending = NULL; p->migration_pending = NULL;
complete = true; complete = true;
} }
task_rq_unlock(rq, p, rf); task_rq_unlock(rq, p, rf);
if (push_task) { if (push_task) {
@ -2213,7 +2217,7 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag
} }
if (complete) if (complete)
goto do_complete; complete_all(&pending->done);
return 0; return 0;
} }
@ -2264,9 +2268,9 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag
if (!stop_pending) if (!stop_pending)
pending->stop_pending = true; pending->stop_pending = true;
refcount_inc(&pending->refs); /* pending->{arg,stop_work} */
if (flags & SCA_MIGRATE_ENABLE) if (flags & SCA_MIGRATE_ENABLE)
p->migration_flags &= ~MDF_PUSH; p->migration_flags &= ~MDF_PUSH;
task_rq_unlock(rq, p, rf); task_rq_unlock(rq, p, rf);
if (!stop_pending) { if (!stop_pending) {
@ -2282,12 +2286,13 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag
if (task_on_rq_queued(p)) if (task_on_rq_queued(p))
rq = move_queued_task(rq, rf, p, dest_cpu); rq = move_queued_task(rq, rf, p, dest_cpu);
p->migration_pending = NULL; if (!pending->stop_pending) {
complete = true; p->migration_pending = NULL;
complete = true;
}
} }
task_rq_unlock(rq, p, rf); task_rq_unlock(rq, p, rf);
do_complete:
if (complete) if (complete)
complete_all(&pending->done); complete_all(&pending->done);
} }
@ -2295,7 +2300,7 @@ do_complete:
wait_for_completion(&pending->done); wait_for_completion(&pending->done);
if (refcount_dec_and_test(&pending->refs)) 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 * Block the original owner of &pending until all subsequent callers
@ -2303,6 +2308,9 @@ do_complete:
*/ */
wait_var_event(&my_pending.refs, !refcount_read(&my_pending.refs)); wait_var_event(&my_pending.refs, !refcount_read(&my_pending.refs));
/* ARGH */
WARN_ON_ONCE(my_pending.stop_pending);
return 0; return 0;
} }