From: Kent Overstreet kent.overstreet@gmail.com
[ 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 kent.overstreet@gmail.com Acked-by: Coly Li colyli@suse.de Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- 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)