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author | Kent Overstreet <kent.overstreet@gmail.com> | 2019-09-03 21:25:45 +0800 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-10-05 13:13:53 +0200 |
commit | 94a379db627aad261074b3f7376e68041081b232 (patch) | |
tree | 292bb0cc44d5ceb0dd020fd3e85b02e4021cd7f9 | |
parent | 4b88669aa2f85d73326ca00f6c862bcf64a9376d (diff) | |
download | linux-stable-94a379db627aad261074b3f7376e68041081b232.tar.gz linux-stable-94a379db627aad261074b3f7376e68041081b232.tar.bz2 linux-stable-94a379db627aad261074b3f7376e68041081b232.zip |
closures: fix a race on wakeup from closure_sync
[ 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>
-rw-r--r-- | drivers/md/bcache/closure.c | 10 |
1 files 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) |