From: Scott Wood Date: Fri, 4 Jan 2019 15:33:21 -0500 Subject: [PATCH 151/342] locking/rt-mutex: Flush block plug on __down_read() Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=0997f874d638be3d2f65de4bf3d9710d1e5bc2d8 __down_read() bypasses the rtmutex frontend to call rt_mutex_slowlock_locked() directly, and thus it needs to call blk_schedule_flush_flug() itself. Cc: stable-rt@vger.kernel.org Signed-off-by: Scott Wood Signed-off-by: Sebastian Andrzej Siewior --- kernel/locking/rwsem-rt.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/locking/rwsem-rt.c b/kernel/locking/rwsem-rt.c index 660e22caf709..f518495bd6cc 100644 --- a/kernel/locking/rwsem-rt.c +++ b/kernel/locking/rwsem-rt.c @@ -1,5 +1,6 @@ /* */ +#include #include #include #include @@ -87,6 +88,14 @@ static int __sched __down_read_common(struct rw_semaphore *sem, int state) if (__down_read_trylock(sem)) return 0; + /* + * If rt_mutex blocks, the function sched_submit_work will not call + * blk_schedule_flush_plug (because tsk_is_pi_blocked would be true). + * We must call blk_schedule_flush_plug here, if we don't call it, + * a deadlock in I/O may happen. + */ + if (unlikely(blk_needs_flush_plug(current))) + blk_schedule_flush_plug(current); might_sleep(); raw_spin_lock_irq(&m->wait_lock);