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

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This reverts commit fa247089de.

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 fa247089de. 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: fa247089de ("dm: requeue IO if mapping table not yet available")
This commit is contained in:
Mikulas Patocka 2024-09-13 15:05:18 +02:00
parent 9c2010bccc
commit c8691cd0fc
2 changed files with 11 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
drivers/md/dm-rq.c
View File

@ -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); map = dm_get_live_table(md, &srcu_idx);
if (unlikely(!map)) { if (unlikely(!map)) {
DMERR_LIMIT("%s: mapping table unavailable, erroring io",
dm_device_name(md));
dm_put_live_table(md, srcu_idx); dm_put_live_table(md, srcu_idx);
return BLK_STS_RESOURCE; return BLK_STS_IOERR;
} }
ti = dm_table_find_target(map, 0); ti = dm_table_find_target(map, 0);
dm_put_live_table(md, srcu_idx); dm_put_live_table(md, srcu_idx);

11
drivers/md/dm.c
View File

@ -2030,10 +2030,15 @@ static void dm_submit_bio(struct bio *bio)
struct dm_table *map; struct dm_table *map;
map = dm_get_live_table(md, &srcu_idx); 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 suspended, queue this IO for later */
if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) || if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))) {
unlikely(!map)) {
if (bio->bi_opf & REQ_NOWAIT) if (bio->bi_opf & REQ_NOWAIT)
bio_wouldblock_error(bio); bio_wouldblock_error(bio);
else if (bio->bi_opf & REQ_RAHEAD) else if (bio->bi_opf & REQ_RAHEAD)