[tip: sched/core] sched/wait: Avoid modifying entry on failed priority registration

[tip-bot2 for Hui Su]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     159b172906110f736fdbd7af8a21d0e0b469f671
Gitweb:        https://git.kernel.org/tip/159b172906110f736fdbd7af8a21d0e0b469f671
Author:        Hui Su <sh_def@xxxxxxx>
AuthorDate:    Sun, 11 Oct 2026 10:50:19 +09:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 13 Oct 2026 13:51:28 +02:00

sched/wait: Avoid modifying entry on failed priority registration

add_wait_queue_priority_exclusive() sets WQ_FLAG_EXCLUSIVE and
WQ_FLAG_PRIORITY before checking whether another priority waiter is
already present. Thus, when registration fails with -EBUSY, the entry
is left unqueued but with modified flags.

There is no need to modify the entry before the failure check. Move the
flag update after the check so that a rejected registration does not
unnecessarily alter the entry.

Signed-off-by: Hui Su <sh_def@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Link: https://patch.msgid.link/20261011015019.4056529-1-sh_def@xxxxxxx
---
 kernel/sched/wait.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index 477e4bf..f8d6d8b 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -54,14 +54,13 @@ int add_wait_queue_priority_exclusive(struct wait_queue_head *wq_head,
 {
 	struct list_head *head = &wq_head->head;
 
-	wq_entry->flags |= WQ_FLAG_EXCLUSIVE | WQ_FLAG_PRIORITY;
-
 	guard(spinlock_irqsave)(&wq_head->lock);
 
 	if (!list_empty(head) &&
 	    (list_first_entry(head, typeof(*wq_entry), entry)->flags & WQ_FLAG_PRIORITY))
 		return -EBUSY;
 
+	wq_entry->flags |= WQ_FLAG_EXCLUSIVE | WQ_FLAG_PRIORITY;
 	list_add(&wq_entry->entry, head);
 	return 0;
 }