linux-kernel - [PATCH v2] epoll: ep_autoremove_wake_function should use list_del_init

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Message-ID: <xm26bki0ulsr.fsf_-_@google.com>
Date:   Wed, 31 May 2023 16:24:20 -0700
From:   Benjamin Segall <bsegall@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Christian Brauner <brauner@...nel.org>,
        Eric Biggers <ebiggers@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: [PATCH v2] epoll: ep_autoremove_wake_function should use
 list_del_init_careful

autoremove_wake_function uses list_del_init_careful, so should epoll's
more aggressive variant. It only doesn't because it was copied from an
older wait.c rather than the most recent.

Fixes: a16ceb139610 ("epoll: autoremove wakers even more aggressively")
Signed-off-by: Ben Segall <bsegall@...gle.com>
Cc: stable@...r.kernel.org
Change-Id: Icca05359250297f091779c9dcf4fefea92ee8c93
---
 fs/eventpoll.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 980483455cc09..266d45c7685b4 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1803,11 +1803,15 @@ static struct timespec64 *ep_timeout_to_timespec(struct timespec64 *to, long ms)
 static int ep_autoremove_wake_function(struct wait_queue_entry *wq_entry,
 				       unsigned int mode, int sync, void *key)
 {
 	int ret = default_wake_function(wq_entry, mode, sync, key);
 
-	list_del_init(&wq_entry->entry);
+	/*
+	 * Pairs with list_empty_careful in ep_poll, and ensures future loop
+	 * iterations see the cause of this wakeup.
+	 */
+	list_del_init_careful(&wq_entry->entry);
 	return ret;
 }
 
 /**
  * ep_poll - Retrieves ready events, and delivers them to the caller-supplied
-- 
2.41.0.rc0.172.g3f132b7071-goog