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sched: Fix modifying donor->blocked on without proper locking

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Introduce an action enum in find_proxy_task() which allows
us to handle work needed to be done outside the mutex.wait_lock
and task.blocked_lock guard scopes.

This ensures proper locking when we clear the donor's blocked_on
pointer in proxy_deactivate(), and the switch statement will be
useful as we add more cases to handle later in this series.

Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://patch.msgid.link/20260324191337.1841376-6-jstultz@google.com
This commit is contained in:
John Stultz 2026-03-24 19:13:20 +00:00 committed by Peter Zijlstra
parent fa4a1ff8ab
commit 56f4b24267
1 changed files with 13 additions and 3 deletions
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16
kernel/sched/core.c
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@ -6568,7 +6568,7 @@ static struct task_struct *proxy_deactivate(struct rq *rq, struct task_struct *d
* as unblocked, as we aren't doing proxy-migrations
* yet (more logic will be needed then).
*/
donor->blocked_on = NULL;
clear_task_blocked_on(donor, NULL);
}
return NULL;
}
@ -6592,6 +6592,7 @@ static struct task_struct *proxy_deactivate(struct rq *rq, struct task_struct *d
static struct task_struct *
find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags *rf)
{
enum { FOUND, DEACTIVATE_DONOR } action = FOUND;
struct task_struct *owner = NULL;
int this_cpu = cpu_of(rq);
struct task_struct *p;
@ -6625,12 +6626,14 @@ find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags *rf)
if (!READ_ONCE(owner->on_rq) || owner->se.sched_delayed) {
/* XXX Don't handle blocked owners/delayed dequeue yet */
return proxy_deactivate(rq, donor);
action = DEACTIVATE_DONOR;
break;
}
if (task_cpu(owner) != this_cpu) {
/* XXX Don't handle migrations yet */
return proxy_deactivate(rq, donor);
action = DEACTIVATE_DONOR;
break;
}
if (task_on_rq_migrating(owner)) {
@ -6688,6 +6691,13 @@ find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags *rf)
*/
}
/* Handle actions we need to do outside of the guard() scope */
switch (action) {
case DEACTIVATE_DONOR:
return proxy_deactivate(rq, donor);
case FOUND:
/* fallthrough */;
}
WARN_ON_ONCE(owner && !owner->on_rq);
return owner;
}