diff options
| author | Fengnan Chang <changfengnan@bytedance.com> | 2026-05-13 17:13:49 +0800 |
|---|---|---|
| committer | Mikulas Patocka <mpatocka@redhat.com> | 2026-05-18 14:27:11 +0200 |
| commit | 5aa0f9231cbacade065cedd8e9b5ebd067231171 (patch) | |
| tree | 1233c51c34d784e26de8a20e197a935999053c3f /drivers/md | |
| parent | 457e32348d606a77f9b20e25e989734189834c07 (diff) | |
dm: limit target bio polling to one shot
dm_poll_bio() is the ->poll_bio() callback for a stacked dm device.
The caller only knows about the dm queue, so it may decide to do a
spinning poll if it thinks a single queue is being polled. Passing those
flags unchanged to the mapped clone lets blk_mq_poll() spin on a target
queue from inside dm_poll_bio().
With io_uring IOPOLL on a dm-stripe target this can keep a task in
dm_poll_bio() -> bio_poll() -> blk_mq_poll()
long enough to trigger an RCU CPU stall, before io_uring gets back to
io_iopoll_check() and its need_resched() check.
Keep dm's ->poll_bio() bounded by forcing one-shot polling for target
bios. The caller can invoke dm_poll_bio() again if it wants to keep
polling, and it also gets a chance to reap completions or reschedule
between passes.
Fixes: f22ecf9c14c1 ("blk-mq: delete task running check in blk_hctx_poll()")
Signed-off-by: Fengnan Chang <changfengnan@bytedance.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Diffstat (limited to 'drivers/md')
| -rw-r--r-- | drivers/md/dm.c | 13 |
1 files changed, 11 insertions, 2 deletions
diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 87011c41ef7b..7287bed6eb64 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -2098,8 +2098,17 @@ static bool dm_poll_dm_io(struct dm_io *io, struct io_comp_batch *iob, WARN_ON_ONCE(!dm_tio_is_normal(&io->tio)); /* don't poll if the mapped io is done */ - if (atomic_read(&io->io_count) > 1) - bio_poll(&io->tio.clone, iob, flags); + if (atomic_read(&io->io_count) > 1) { + /* + * DM hides the target queues from the upper poller, which may + * decide it is safe to spin on a single stacked queue. Do not + * pass that spinning policy down to a target queue: one slow + * clone could keep the task inside dm_poll_bio() for a long + * time. Poll target bios once and let the caller decide + * whether to keep polling, reap completions or reschedule. + */ + bio_poll(&io->tio.clone, iob, flags | BLK_POLL_ONESHOT); + } /* bio_poll holds the last reference */ return atomic_read(&io->io_count) == 1; |