Revert "dm: requeue IO if mapping table not yet available"

This reverts commit fa247089de9936a46e290d4724cb5f0b845600f5.

The following sequence of commands causes a livelock - there will be
workqueue process looping and consuming 100% CPU:

dmsetup create --notable test
truncate -s 1MiB testdata
losetup /dev/loop0 testdata
dmsetup load test --table '0 2048 linear /dev/loop0 0'
dd if=/dev/zero of=/dev/dm-0 bs=16k count=1 conv=fdatasync

The livelock is caused by the commit fa247089de99. The commit claims that
it fixes a race condition, however, it is unknown what the actual race
condition is and what program is involved in the race condition.

When the inactive table is loaded, the nodes /dev/dm-0 and
/sys/block/dm-0 are created. /dev/dm-0 has zero size at this point. When
the device is suspended and resumed, the nodes /dev/mapper/test and
/dev/disk/* are created.

If some program opens a block device before it is created by dmsetup or
lvm, the program is buggy, so dm could just report an error as it used to
do before.

Reported-by: Zdenek Kabelac <zkabelac@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Fixes: fa247089de99 ("dm: requeue IO if mapping table not yet available")

diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index f7e9a3632eb3d941aa8656f7596061dc458cc77c..499f8cc8a39fbff2851cbeaaa9fda2fb49f1c022 100644 (file)
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -496,8 +496,10 @@ static blk_status_t dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
 
                map = dm_get_live_table(md, &srcu_idx);
                if (unlikely(!map)) {
+                       DMERR_LIMIT("%s: mapping table unavailable, erroring io",
+                                   dm_device_name(md));
                        dm_put_live_table(md, srcu_idx);
-                       return BLK_STS_RESOURCE;
+                       return BLK_STS_IOERR;
                }
                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 87bb903034358234b3112bc9695a9b46403838d7..ff4a6b570b7644ee0097185b0468117d2f220ba7 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2030,10 +2030,15 @@ 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, or map not yet available, queue this IO for later */
-       if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) ||
-           unlikely(!map)) {
+       /* If suspended, queue this IO for later */
+       if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))) {
                if (bio->bi_opf & REQ_NOWAIT)
                        bio_wouldblock_error(bio);
                else if (bio->bi_opf & REQ_RAHEAD)