[PATCH 5.9 357/757] dm: fix missing imposition of queue_limits from dm_wq_work() thread

Greg Kroah-Hartman
2020-10-27T15:56:42Z

From: Mike Snitzer <snitzer@redhat.com>

[ Upstream commit 0c2915b8c6db108b1dfb240391cc5a175f97f15b ]

If a DM device was suspended when bios were issued to it, those bios
would be deferred using queue_io(). Once the DM device was resumed
dm_process_bio() could be called by dm_wq_work() for original bio that
still needs splitting. dm_process_bio()'s check for current->bio_list
(meaning call chain is within ->submit_bio) as a prerequisite for
calling blk_queue_split() for "abnormal IO" would result in
dm_process_bio() never imposing corresponding queue_limits
(e.g. discard_granularity, discard_max_bytes, etc).

Fix this by always having dm_wq_work() resubmit deferred bios using
submit_bio_noacct().

Side-effect is blk_queue_split() is always called for "abnormal IO" from
->submit_bio, be it from application thread or dm_wq_work() workqueue,
so proper bio splitting and depth-first bio submission is performed.
For sake of clarity, remove current->bio_list check before call to
blk_queue_split().

Also, remove dm_wq_work()'s use of dm_{get,put}_live_table() -- no
longer needed since IO will be reissued in terms of ->submit_bio.
And rename bio variable from 'c' to 'bio'.

Fixes: cf9c37865557 ("dm: fix comment in dm_process_bio()")
Reported-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/md/dm.c | 34 +++++++++-------------------------
1 file changed, 9 insertions(+), 25 deletions(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 6ed05ca65a0f8..b060a28ff1c6d 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1744,17 +1744,11 @@ static blk_qc_t dm_process_bio(struct mapped_device *md,
}

/*
- * If in ->submit_bio we need to use blk_queue_split(), otherwise
- * queue_limits for abnormal requests (e.g. discard, writesame, etc)
- * won't be imposed.
- * If called from dm_wq_work() for deferred bio processing, bio
- * was already handled by following code with previous ->submit_bio.
+ * Use blk_queue_split() for abnormal IO (e.g. discard, writesame, etc)
+ * otherwise associated queue_limits won't be imposed.
*/
- if (current->bio_list) {
- if (is_abnormal_io(bio))
- blk_queue_split(&bio);
- /* regular IO is split by __split_and_process_bio */
- }
+ if (is_abnormal_io(bio))
+ blk_queue_split(&bio);

if (dm_get_md_type(md) == DM_TYPE_NVME_BIO_BASED)
return __process_bio(md, map, bio, ti);
@@ -2461,29 +2455,19 @@ static int dm_wait_for_completion(struct mapped_device *md, long task_state)
*/
static void dm_wq_work(struct work_struct *work)
{
- struct mapped_device *md = container_of(work, struct mapped_device,
- work);
- struct bio *c;
- int srcu_idx;
- struct dm_table *map;
-
- map = dm_get_live_table(md, &srcu_idx);
+ struct mapped_device *md = container_of(work, struct mapped_device, work);
+ struct bio *bio;

while (!test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) {
spin_lock_irq(&md->deferred_lock);
- c = bio_list_pop(&md->deferred);
+ bio = bio_list_pop(&md->deferred);
spin_unlock_irq(&md->deferred_lock);

- if (!c)
+ if (!bio)
break;

- if (dm_request_based(md))
- (void) submit_bio_noacct(c);
- else
- (void) dm_process_bio(md, map, c);
+ submit_bio_noacct(bio);
}
-
- dm_put_live_table(md, srcu_idx);
}

static void dm_queue_flush(struct mapped_device *md)
--
2.25.1