Commit a22a9602 authored Sep 03, 2019 by Kent Overstreet Committed by Jens Axboe Sep 03, 2019

closures: fix a race on wakeup from closure_sync



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 <kent.overstreet@gmail.com>
Acked-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent d66c9920

drivers/md/bcache/closure.c

+8 −2

Original line number	Diff line number	Diff line
		@@ -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)

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