drivers/md/raid1.c

568 	 * barrier unit which start_sector belongs to.
942  * To do this we raise a 'barrier'.
943  * The 'barrier' is a counter that can be raised multiple times
946  * We can only raise the barrier if there is no pending IO.
948  * We choose only to raise the barrier if no-one is waiting for the
949  * barrier to go down.  This means that as soon as an IO request
950  * is ready, no other operations which require a barrier will start
975 	atomic_inc(&conf->barrier[idx]);
977 	 * In raise_barrier() we firstly increase conf->barrier[idx] then
979 	 * increase conf->nr_pending[idx] then check conf->barrier[idx].
980 	 * A memory barrier here to make sure conf->nr_pending[idx] won't
981 	 * be fetched before conf->barrier[idx] is increased. Otherwise
989 	 *    existing in corresponding I/O barrier bucket.
990 	 * C: while conf->barrier[idx] >= RESYNC_DEPTH, meaning reaches
991 	 *    max resync count which allowed on current I/O barrier bucket.
996 			     atomic_read(&conf->barrier[idx]) < RESYNC_DEPTH) ||
1001 		atomic_dec(&conf->barrier[idx]);
1017 	BUG_ON(atomic_read(&conf->barrier[idx]) <= 0);
1019 	atomic_dec(&conf->barrier[idx]);
1032 	 * conf->resync_lock when there is no barrier raised in same
1033 	 * barrier unit bucket. Also if the array is frozen, I/O
1039 	 * check conf->barrier[idx]. In raise_barrier() we firstly increase
1040 	 * conf->barrier[idx], then check conf->nr_pending[idx]. A memory
1041 	 * barrier is necessary here to make sure conf->barrier[idx] won't be
1049 	 * here. If during we check conf->barrier[idx], the array is
1050 	 * frozen (conf->array_frozen is 1), and chonf->barrier[idx] is
1057 	    !atomic_read(&conf->barrier[idx]))
1062 	 * should be decreased before waiting for barrier to drop.
1075 	/* Wait for the barrier in same barrier unit bucket to drop. */
1083 				!atomic_read(&conf->barrier[idx]),
1103 	 * conf->barrier[idx] here, memory barrier is unnecessary as well.
1183 	 * barrier bucket index which this I/O request hits. When all sync and
1339 	 * Still need barrier for READ in case that whole
2755  * This is achieved by tracking pending requests and a 'barrier' concept
2854 	/* make sure good_sectors won't go across barrier unit boundary */
3091 	conf->barrier = kcalloc(BARRIER_BUCKETS_NR,
3093 	if (!conf->barrier)
3190 		kfree(conf->barrier);
3302 	kfree(conf->barrier);
3343 	 * Then raise a device barrier and wait until all IO stops.