linux-kernel - [PATCH v3 3/5] signalfd: use wake_up

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Date:   Wed,  8 Dec 2021 17:04:53 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Benjamin LaHaise <bcrl@...ck.org>
Cc:     linux-aio@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ramji Jiyani <ramjiyani@...gle.com>,
        Christoph Hellwig <hch@....de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Martijn Coenen <maco@...roid.com>, stable@...r.kernel.org
Subject: [PATCH v3 3/5] signalfd: use wake_up_pollfree()

From: Eric Biggers <ebiggers@...gle.com>

wake_up_poll() uses nr_exclusive=1, so it's not guaranteed to wake up
all exclusive waiters.  Yet, POLLFREE *must* wake up all waiters.  epoll
and aio poll are fortunately not affected by this, but it's very
fragile.  Thus, the new function wake_up_pollfree() has been introduced.

Convert signalfd to use wake_up_pollfree().

Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
Fixes: d80e731ecab4 ("epoll: introduce POLLFREE to flush ->signalfd_wqh before kfree()")
Cc: stable@...r.kernel.org
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
---
 fs/signalfd.c | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/fs/signalfd.c b/fs/signalfd.c
index 040e1cf905282..65ce0e72e7b95 100644
--- a/fs/signalfd.c
+++ b/fs/signalfd.c
@@ -35,17 +35,7 @@
 
 void signalfd_cleanup(struct sighand_struct *sighand)
 {
-	wait_queue_head_t *wqh = &sighand->signalfd_wqh;
-	/*
-	 * The lockless check can race with remove_wait_queue() in progress,
-	 * but in this case its caller should run under rcu_read_lock() and
-	 * sighand_cachep is SLAB_TYPESAFE_BY_RCU, we can safely return.
-	 */
-	if (likely(!waitqueue_active(wqh)))
-		return;
-
-	/* wait_queue_entry_t->func(POLLFREE) should do remove_wait_queue() */
-	wake_up_poll(wqh, EPOLLHUP | POLLFREE);
+	wake_up_pollfree(&sighand->signalfd_wqh);
 }
 
 struct signalfd_ctx {
-- 
2.34.1