From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sasha Levin Subject: [PATCH AUTOSEL 5.3 159/203] closures: fix a race on wakeup from closure_sync Date: Sun, 22 Sep 2019 14:43:05 -0400 Message-ID: <20190922184350.30563-159-sashal@kernel.org> References: <20190922184350.30563-1-sashal@kernel.org> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20190922184350.30563-1-sashal@kernel.org> Sender: linux-kernel-owner@vger.kernel.org To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Kent Overstreet , Coly Li , Jens Axboe , Sasha Levin , linux-bcache@vger.kernel.org List-Id: linux-bcache@vger.kernel.org From: Kent Overstreet [ Upstream commit a22a9602b88fabf10847f238ff81fde5f906fef7 ] The race was when a thread using closure_sync() notices cl->s->done == 1 before the thread calling closure_put() calls wake_up_process(). Then, it's possible for that thread to return and exit just before wake_up_process() is called - so we're trying to wake up a process that no longer exists. rcu_read_lock() is sufficient to protect against this, as there's an rcu barrier somewhere in the process teardown path. Signed-off-by: Kent Overstreet Acked-by: Coly Li Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin --- drivers/md/bcache/closure.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/drivers/md/bcache/closure.c b/drivers/md/bcache/closure.c index 73f5319295bc9..c12cd809ab193 100644 --- a/drivers/md/bcache/closure.c +++ b/drivers/md/bcache/closure.c @@ -105,8 +105,14 @@ struct closure_syncer { static void closure_sync_fn(struct closure *cl) { - cl->s->done = 1; - wake_up_process(cl->s->task); + struct closure_syncer *s = cl->s; + struct task_struct *p; + + rcu_read_lock(); + p = READ_ONCE(s->task); + s->done = 1; + wake_up_process(p); + rcu_read_unlock(); } void __sched __closure_sync(struct closure *cl) -- 2.20.1