From: Kent Overstreet <kent.overstreet@xxxxxxxxx>
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@xxxxxxxxx>
Acked-by: Coly Li <colyli@xxxxxxx>
---
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 73f5319295bc..c12cd809ab19 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)
--
2.16.4
