From: Ben Hutchings <ben@decadent.org.uk>
To: stable@vger.kernel.org
Cc: Lee Jones <lee.jones@linaro.org>,
"Luis Claudio R. Goncalves" <lgoncalv@redhat.com>,
Florian Fainelli <f.fainelli@gmail.com>
Subject: [PATCH 08/13] futex: Fix (possible) missed wakeup
Date: Sun, 28 Mar 2021 22:42:32 +0200 [thread overview]
Message-ID: <YGDqOPquwh/m9sL9@decadent.org.uk> (raw)
In-Reply-To: <YGDp1qJOCUJmE1Ty@decadent.org.uk>
[-- Attachment #1: Type: text/plain, Size: 1909 bytes --]
From: Peter Zijlstra <peterz@infradead.org>
commit b061c38bef43406df8e73c5be06cbfacad5ee6ad upstream.
We must not rely on wake_q_add() to delay the wakeup; in particular
commit:
1d0dcb3ad9d3 ("futex: Implement lockless wakeups")
moved wake_q_add() before smp_store_release(&q->lock_ptr, NULL), which
could result in futex_wait() waking before observing ->lock_ptr ==
NULL and going back to sleep again.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 1d0dcb3ad9d3 ("futex: Implement lockless wakeups")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
kernel/futex.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c
index 60be2d3cfdd7..5677fbb97aea 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1553,11 +1553,7 @@ static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
return;
- /*
- * Queue the task for later wakeup for after we've released
- * the hb->lock. wake_q_add() grabs reference to p.
- */
- wake_q_add(wake_q, p);
+ get_task_struct(p);
__unqueue_futex(q);
/*
* The waiting task can free the futex_q as soon as
@@ -1566,6 +1562,13 @@ static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
* store to lock_ptr from getting ahead of the plist_del.
*/
smp_store_release(&q->lock_ptr, NULL);
+
+ /*
+ * Queue the task for later wakeup for after we've released
+ * the hb->lock. wake_q_add() grabs reference to p.
+ */
+ wake_q_add(wake_q, p);
+ put_task_struct(p);
}
/*
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
next prev parent reply other threads:[~2021-03-28 20:43 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-28 20:40 [PATCH 01/13] futex: Use smp_store_release() in mark_wake_futex() Ben Hutchings
2021-03-28 20:41 ` [PATCH 02/13] futex,rt_mutex: Introduce rt_mutex_init_waiter() Ben Hutchings
2021-03-28 20:41 ` [PATCH 03/13] futex: Rework futex_lock_pi() to use rt_mutex_*_proxy_lock() Ben Hutchings
2021-03-28 20:41 ` [PATCH 04/13] futex: Drop hb->lock before enqueueing on the rtmutex Ben Hutchings
2021-03-28 20:42 ` [PATCH 05/13] futex: Avoid freeing an active timer Ben Hutchings
2021-03-28 20:42 ` [PATCH 06/13] futex,rt_mutex: Fix rt_mutex_cleanup_proxy_lock() Ben Hutchings
2021-03-28 20:42 ` [PATCH 07/13] futex: Handle early deadlock return correctly Ben Hutchings
2021-03-28 20:42 ` Ben Hutchings [this message]
2021-03-28 20:42 ` [PATCH 09/13] locking/futex: Allow low-level atomic operations to return -EAGAIN Ben Hutchings
2021-03-28 20:42 ` [PATCH 10/13] arm64: futex: Bound number of LDXR/STXR loops in FUTEX_WAKE_OP Ben Hutchings
2021-03-28 20:42 ` [PATCH 11/13] futex: Prevent robust futex exit race Ben Hutchings
2021-03-28 20:43 ` [PATCH 12/13] futex: Fix incorrect should_fail_futex() handling Ben Hutchings
2021-03-28 20:43 ` [PATCH 13/13] futex: Handle transient "ownerless" rtmutex state correctly Ben Hutchings
2021-03-29 5:50 ` [PATCH 01/13] futex: Use smp_store_release() in mark_wake_futex() Greg KH
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YGDqOPquwh/m9sL9@decadent.org.uk \
--to=ben@decadent.org.uk \
--cc=f.fainelli@gmail.com \
--cc=lee.jones@linaro.org \
--cc=lgoncalv@redhat.com \
--cc=stable@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox