5.10-stable review patch. If anyone has any objections, please let me know.
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From: Mikulas Patocka mpatocka@redhat.com
[ Upstream commit c8691cd0fc11197515ed148de0780d927bfca38b ]
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") Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/md/dm-rq.c | 4 +++- drivers/md/dm.c | 11 ++++++++--- 2 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c index 5f933dbb0152c..7762bde40963e 100644 --- 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 b56ea42ab7d2b..4fdf0e666777a 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -1696,10 +1696,15 @@ 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, 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)