linux-kernel - [PATCH 1/1] epoll: remove wrong assert that ep_poll

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Date:   Tue,  8 Jan 2019 11:01:21 +0100
From:   Roman Penyaev <rpenyaev@...e.de>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Roman Penyaev <rpenyaev@...e.de>, Davidlohr Bueso <dbueso@...e.de>,
        Jason Baron <jbaron@...mai.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/1] epoll: remove wrong assert that ep_poll_callback is always called with irqs off

That was wrong assumption that all drivers disable irqs before waking up
a wait queue.  Even assert line is removed the whole logic stays correct:
epoll always locks rwlock with irqs disabled and by itself does not call
from interrupts, thus it is up to driver how to call wake_up_locked(),
because if driver does not handle any interrupts (like fuse in the the
report) of course it is safe on its side to take a simple spin_lock.

Signed-off-by: Roman Penyaev <rpenyaev@...e.de>
Reported-by: syzbot+aea82bf9ee6ffd9a79d9@...kaller.appspotmail.com
Cc: Davidlohr Bueso <dbueso@...e.de>
Cc: Jason Baron <jbaron@...mai.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-fsdevel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
---
 fs/eventpoll.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index f307c8679027..f5f88250cdf2 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1217,12 +1217,6 @@ static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, v
 	__poll_t pollflags = key_to_poll(key);
 	int ewake = 0;
 
-	/*
-	 * Called by irq context or interrupts are disabled by the wake_up_*poll
-	 * callers.
-	 */
-	lockdep_assert_irqs_disabled();
-
 	read_lock(&ep->lock);
 
 	ep_set_busy_poll_napi_id(epi);
-- 
2.19.1