From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 052D815CD78; Sun, 24 Nov 2024 12:41:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732452089; cv=none; b=aOX5Le42uM1n2QeZDvIArzLXDfE9N2OIPy7NFyuoIr9AoWtEDuLa51Sv/SdN8DlSaNUoGGm2oK5ynlBIPXDpiMyCpqR3lFttoLmNmaQ994C6/60mgGYJ1Sp7EhpFRdEYyu/X9bMXcPgNbM4cucVXzYk39sS+DxRO5/qvBth2EyY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732452089; c=relaxed/simple; bh=0D9xhHepQPzxIJtCZNP6S3YT7qLq7nKYk3vHfPFPVVg=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=rYKeaywFYynRaZ/uovi+lFW6XtkgSNB5gMlWiZPG74XTpSHnHT4Dq3XuiAVmOwwAJHnBjBW3y4yGw5hu9WQ466/TtB2Xjh6EunPpY8HZ3/eleYSKurJ2kTo4grARyiqd3a6m1ZAnGiP20dNpVgxjLKInFwr0TIHGTiwOsgmH0C4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ejAjUmCQ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ejAjUmCQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EE947C4CECC; Sun, 24 Nov 2024 12:41:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1732452088; bh=0D9xhHepQPzxIJtCZNP6S3YT7qLq7nKYk3vHfPFPVVg=; h=From:To:Cc:Subject:Date:From; b=ejAjUmCQwrHmLrgd1x+ca6/9HryM6rf1UVr6ESRMl/dCbQLcFtScX3+zt4QwVT6mG klyg+JUDTtK6lIUogGkLNxt1FFo+NUjXdzlqs2SsLRszNiv+0tACTwgkREzzsZ8zx9 2Jn04yhtlLIwaCoXx15pA1/HkdgIcOoLIIRMx9sGmjUwi6Hej25qZtb0nzrjp6jbEn doA/LGRsR/8gQeLKn5YSwKEjMIettr5PrHZn1P4wsRwMBn5KcWRuB6SktHTb6CDjTd f84s8FRrNDqtXHkEhDz9SSdlOER/qYAoZQu2Q1sLxLQRcXuDP5Lj5rH0uMNHdLaBIc 6cEv6FRYEfKnQ== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Christian Brauner , Jan Kara , syzbot+3b6b32dc50537a49bb4a@syzkaller.appspotmail.com, Sasha Levin , viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org Subject: [PATCH AUTOSEL 6.1 1/7] epoll: annotate racy check Date: Sun, 24 Nov 2024 07:41:12 -0500 Message-ID: <20241124124126.3336691-1-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.1.119 Content-Transfer-Encoding: 8bit From: Christian Brauner [ Upstream commit 6474353a5e3d0b2cf610153cea0c61f576a36d0a ] Epoll relies on a racy fastpath check during __fput() in eventpoll_release() to avoid the hit of pointlessly acquiring a semaphore. Annotate that race by using WRITE_ONCE() and READ_ONCE(). Link: https://lore.kernel.org/r/66edfb3c.050a0220.3195df.001a.GAE@google.com Link: https://lore.kernel.org/r/20240925-fungieren-anbauen-79b334b00542@brauner Reviewed-by: Jan Kara Reported-by: syzbot+3b6b32dc50537a49bb4a@syzkaller.appspotmail.com Signed-off-by: Christian Brauner Signed-off-by: Sasha Levin --- fs/eventpoll.c | 6 ++++-- include/linux/eventpoll.h | 2 +- 2 files changed, 5 insertions(+), 3 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 7221072f39fad..f296ffb57d052 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -703,7 +703,8 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi) to_free = NULL; head = file->f_ep; if (head->first == &epi->fllink && !epi->fllink.next) { - file->f_ep = NULL; + /* See eventpoll_release() for details. */ + WRITE_ONCE(file->f_ep, NULL); if (!is_file_epoll(file)) { struct epitems_head *v; v = container_of(head, struct epitems_head, epitems); @@ -1467,7 +1468,8 @@ static int attach_epitem(struct file *file, struct epitem *epi) spin_unlock(&file->f_lock); goto allocate; } - file->f_ep = head; + /* See eventpoll_release() for details. */ + WRITE_ONCE(file->f_ep, head); to_free = NULL; } hlist_add_head_rcu(&epi->fllink, file->f_ep); diff --git a/include/linux/eventpoll.h b/include/linux/eventpoll.h index 3337745d81bd6..0c0d00fcd131f 100644 --- a/include/linux/eventpoll.h +++ b/include/linux/eventpoll.h @@ -42,7 +42,7 @@ static inline void eventpoll_release(struct file *file) * because the file in on the way to be removed and nobody ( but * eventpoll ) has still a reference to this file. */ - if (likely(!file->f_ep)) + if (likely(!READ_ONCE(file->f_ep))) return; /* -- 2.43.0