raid5-cache: fix a deadlock in superblock write (8e018c21) · Commits · 戴 / test

drivers/md/raid5-cache.c

+15 −31

Original line number	Diff line number	Diff line
		@@ -96,7 +96,6 @@ struct r5l_log {
		spinlock_t no_space_stripes_lock;

		bool need_cache_flush;
		bool in_teardown;
		};

		/*
		@@ -704,31 +703,22 @@ static void r5l_write_super_and_discard_space(struct r5l_log *log,

		mddev = log->rdev->mddev;
		/*
		* This is to avoid a deadlock. r5l_quiesce holds reconfig_mutex and
		* wait for this thread to finish. This thread waits for
		* MD_CHANGE_PENDING clear, which is supposed to be done in
		* md_check_recovery(). md_check_recovery() tries to get
		* reconfig_mutex. Since r5l_quiesce already holds the mutex,
		* md_check_recovery() fails, so the PENDING never get cleared. The
		* in_teardown check workaround this issue.
		* Discard could zero data, so before discard we must make sure
		* superblock is updated to new log tail. Updating superblock (either
		* directly call md_update_sb() or depend on md thread) must hold
		* reconfig mutex. On the other hand, raid5_quiesce is called with
		* reconfig_mutex hold. The first step of raid5_quiesce() is waitting
		* for all IO finish, hence waitting for reclaim thread, while reclaim
		* thread is calling this function and waitting for reconfig mutex. So
		* there is a deadlock. We workaround this issue with a trylock.
		* FIXME: we could miss discard if we can't take reconfig mutex
		*/
		if (!log->in_teardown) {
		set_mask_bits(&mddev->flags, 0,
		BIT(MD_CHANGE_DEVS) \| BIT(MD_CHANGE_PENDING));
		md_wakeup_thread(mddev->thread);
		wait_event(mddev->sb_wait,
		!test_bit(MD_CHANGE_PENDING, &mddev->flags) \|\|
		log->in_teardown);
		/*
		* r5l_quiesce could run after in_teardown check and hold
		* mutex first. Superblock might get updated twice.
		*/
		if (log->in_teardown)
		md_update_sb(mddev, 1);
		} else {
		WARN_ON(!mddev_is_locked(mddev));
		if (!mddev_trylock(mddev))
		return;
		md_update_sb(mddev, 1);
		}
		mddev_unlock(mddev);

		/* discard IO error really doesn't matter, ignore it */
		if (log->last_checkpoint < end) {
		@@ -827,7 +817,6 @@ void r5l_quiesce(struct r5l_log *log, int state)
		if (!log \|\| state == 2)
		return;
		if (state == 0) {
		log->in_teardown = 0;
		/*
		* This is a special case for hotadd. In suspend, the array has
		* no journal. In resume, journal is initialized as well as the
		@@ -838,11 +827,6 @@ void r5l_quiesce(struct r5l_log *log, int state)
		log->reclaim_thread = md_register_thread(r5l_reclaim_thread,
		log->rdev->mddev, "reclaim");
		} else if (state == 1) {
		/*
		* at this point all stripes are finished, so io_unit is at
		* least in STRIPE_END state
		*/
		log->in_teardown = 1;
		/* make sure r5l_write_super_and_discard_space exits */
		mddev = log->rdev->mddev;
		wake_up(&mddev->sb_wait);

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