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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>
This commit is contained in:
Kent Overstreet 2019-09-03 21:25:45 +08:00 committed by Jens Axboe
parent d66c9920c0
commit a22a9602b8
1 changed files with 8 additions and 2 deletions
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10
drivers/md/bcache/closure.c
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@ -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)