[dm-devel] Patch "dm: requeue IO if mapping table not yet available" has been added to the 5.16-stable tree

[Sasha Levin <sashal@kernel.org>]

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 5.16-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-5.16 subdirectory.

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



commit 6cc54e620523c9169f8d37eb21a61840127740ab
Author: Mike Snitzer <snitzer@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@huawei.com>
    Signed-off-by: Mike Snitzer <snitzer@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index 579ab6183d4d..dffeb47a9efb 100644
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -499,8 +499,13 @@ 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 5fd3660e07b5..af12c0accb59 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1587,15 +1587,10 @@ static void 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)

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