md/raid5: release batch_last before waiting for another stripe_head

When raid5_get_active_stripe is called with a ctx containing a stripe_head in
its batch_last pointer, it can cause a deadlock if the task sleeps waiting on
another stripe_head to become available. The stripe_head held by batch_last
can be blocking the advancement of other stripe_heads, leading to no
stripe_heads being released so raid5_get_active_stripe waits forever.

Like with the quiesce state handling earlier in the function, batch_last
needs to be released by raid5_get_active_stripe before it waits for another
stripe_head.

Fixes: 3312e6c ("md/raid5: Keep a reference to last stripe_head for batch")
Cc: [email protected] # v6.0+
Signed-off-by: David Jeffery <[email protected]>
Reviewed-by: Logan Gunthorpe <[email protected]>
Signed-off-by: Song Liu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: David Jeffery

drivers/md/raid5.c

@@ -854,6 +854,13 @@ struct stripe_head *raid5_get_active_stripe(struct r5conf *conf,
 
 		set_bit(R5_INACTIVE_BLOCKED, &conf->cache_state);
 		r5l_wake_reclaim(conf->log, 0);
+
+		/* release batch_last before wait to avoid risk of deadlock */
+		if (ctx && ctx->batch_last) {
+			raid5_release_stripe(ctx->batch_last);
+			ctx->batch_last = NULL;
+		}
+
 		wait_event_lock_irq(conf->wait_for_stripe,
 				    is_inactive_blocked(conf, hash),
 				    *(conf->hash_locks + hash));