[dm-devel] Patch "dm: requeue IO if mapping table not yet available" has been added to the 5.15-stable tree

[Sasha Levin]

This is a note to let you know that I've just added the patch titled

    dm: requeue IO if mapping table not yet available

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     dm-requeue-io-if-mapping-table-not-yet-available.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable at vger.kernel.org> know about it.



commit 2453401f663a14f796b6297823bab9037e2efe6d
Author: Mike Snitzer <snitzer at redhat.com>
Date:   Tue Feb 22 13:28:12 2022 -0500

    dm: requeue IO if mapping table not yet available
    
    [ Upstream commit fa247089de9936a46e290d4724cb5f0b845600f5 ]
    
    Update both bio-based and request-based DM to requeue IO if the
    mapping table not available.
    
    This race of IO being submitted before the DM device ready is so
    narrow, yet possible for initial table load given that the DM device's
    request_queue is created prior, that it best to requeue IO to handle
    this unlikely case.
    
    Reported-by: Zhang Yi <yi.zhang at huawei.com>
    Signed-off-by: Mike Snitzer <snitzer at redhat.com>
    Signed-off-by: Sasha Levin <sashal at kernel.org>

diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index a896dea9750e..53a9b16c7b2e 100644
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -500,8 +500,13 @@ static blk_status_t dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
 
 	if (unlikely(!ti)) {
 		int srcu_idx;
-		struct dm_table *map = dm_get_live_table(md, &srcu_idx);
+		struct dm_table *map;
 
+		map = dm_get_live_table(md, &srcu_idx);
+		if (unlikely(!map)) {
+			dm_put_live_table(md, srcu_idx);
+			return BLK_STS_RESOURCE;
+		}
 		ti = dm_table_find_target(map, 0);
 		dm_put_live_table(md, srcu_idx);
 	}
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 443478a08857..36449422e7e0 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1594,15 +1594,10 @@ static blk_qc_t dm_submit_bio(struct bio *bio)
 	struct dm_table *map;
 
 	map = dm_get_live_table(md, &srcu_idx);
-	if (unlikely(!map)) {
-		DMERR_LIMIT("%s: mapping table unavailable, erroring io",
-			    dm_device_name(md));
-		bio_io_error(bio);
-		goto out;
-	}
 
-	/* If suspended, queue this IO for later */
-	if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))) {
+	/* If suspended, or map not yet available, queue this IO for later */
+	if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) ||
+	    unlikely(!map)) {
 		if (bio->bi_opf & REQ_NOWAIT)
 			bio_wouldblock_error(bio);
 		else if (bio->bi_opf & REQ_RAHEAD)