dm: remove unnecessary current->bio_list check when submitting split bio

The depth-first splitting is introduced in commit 18a25da84354 ("dm:
ensure bio submission follows a depth-first tree walk"), which is used
to fix the potential deadlock in case of the misordering handling of
bios caused by bio_list. There're two paths submitting split bios,
dm_wq_work() from worker thread and submit_bio() from application. Back
upon that time, dm_wq_work() thread calls __split_and_process_bio()
directly and thus will not trigger this issue since bio_list doesn't
exist here. So this issue will only be triggered from application
calling submit_bio(), and the fix has to check if current->bio_list is
non-NULL to distinguish this case.

However since commit 0c2915b8c6db1 ("dm: fix missing imposition of
queue_limits from dm_wq_work() thread"), dm_wq_work() thread calls
submit_bio_noacct() and thus also uses bio_list. Since then all entries
into __split_and_process_bio() are under protection of bio_list, and
thus the checking of current->bio_list when determinning if the
depth-first principle should be used, seems kind of nonsense. After all
the checking always succeeds now.

Fixes: 0c2915b8c6db1 ("dm: fix missing imposition of queue_limits from dm_wq_work() thread")
Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 4e0cbfe3f14d434f9fefeae37b1d6f71e79b4f63..9408df43ba757de32ccf1eedf8094ae2fcecd42d 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1590,7 +1590,7 @@ static blk_qc_t __split_and_process_bio(struct mapped_device *md,
                ci.sector_count = bio_sectors(bio);
                while (ci.sector_count && !error) {
                        error = __split_and_process_non_flush(&ci);
-                       if (current->bio_list && ci.sector_count && !error) {
+                       if (ci.sector_count && !error) {
                                /*
                                 * Remainder must be passed to submit_bio_noacct()
                                 * so that it gets handled *after* bios already submitted