Commit f6eca2d4 authored Oct 17, 2017 by Nate Dailey Committed by Shaohua Li Nov 01, 2017

raid1: prevent freeze_array/wait_all_barriers deadlock



If freeze_array is attempted in the middle of close_sync/
wait_all_barriers, deadlock can occur.

freeze_array will wait for nr_pending and nr_queued to line up.
wait_all_barriers increments nr_pending for each barrier bucket, one
at a time, but doesn't actually issue IO that could be counted in
nr_queued. So freeze_array is blocked until wait_all_barriers
completes and allow_all_barriers runs. At the same time, when
_wait_barrier sees array_frozen == 1, it stops and waits for
freeze_array to complete.

Prevent the deadlock by making close_sync call _wait_barrier and
_allow_barrier for one bucket at a time, instead of deferring the
_allow_barrier calls until after all _wait_barriers are complete.

Signed-off-by: Nate Dailey <nate.dailey@stratus.com>
Fix: fd76863e(RAID1: a new I/O barrier implementation to remove resync window)
Reviewed-by: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org (v4.11)
Signed-off-by: Shaohua Li <shli@fb.com>

parent ae89fd3d

drivers/md/raid1.c

+6 −18

Original line number	Diff line number	Diff line
		@@ -989,14 +989,6 @@ static void wait_barrier(struct r1conf *conf, sector_t sector_nr)
		_wait_barrier(conf, idx);
		}

		static void wait_all_barriers(struct r1conf *conf)
		{
		int idx;

		for (idx = 0; idx < BARRIER_BUCKETS_NR; idx++)
		_wait_barrier(conf, idx);
		}

		static void _allow_barrier(struct r1conf *conf, int idx)
		{
		atomic_dec(&conf->nr_pending[idx]);
		@@ -1010,14 +1002,6 @@ static void allow_barrier(struct r1conf *conf, sector_t sector_nr)
		_allow_barrier(conf, idx);
		}

		static void allow_all_barriers(struct r1conf *conf)
		{
		int idx;

		for (idx = 0; idx < BARRIER_BUCKETS_NR; idx++)
		_allow_barrier(conf, idx);
		}

		/* conf->resync_lock should be held */
		static int get_unqueued_pending(struct r1conf *conf)
		{
		@@ -1645,8 +1629,12 @@ static void print_conf(struct r1conf *conf)

		static void close_sync(struct r1conf *conf)
		{
		wait_all_barriers(conf);
		allow_all_barriers(conf);
		int idx;

		for (idx = 0; idx < BARRIER_BUCKETS_NR; idx++) {
		_wait_barrier(conf, idx);
		_allow_barrier(conf, idx);
		}

		mempool_destroy(conf->r1buf_pool);
		conf->r1buf_pool = NULL;

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