On 5/22/25 11:14 AM, Bart Van Assche wrote:
blk_mq_freeze_queue() never terminates if one or more bios are on the plug list and if the block device driver defines a .submit_bio() method. This is the case for device mapper drivers. The deadlock happens because blk_mq_freeze_queue() waits for q_usage_counter to drop to zero, because a queue reference is held by bios on the plug list and because the __bio_queue_enter() call in __submit_bio() waits for the queue to be unfrozen.
This patch fixes the following deadlock:
Workqueue: dm-51_zwplugs blk_zone_wplug_bio_work Call trace: __schedule+0xb08/0x1160 schedule+0x48/0xc8 __bio_queue_enter+0xcc/0x1d0 __submit_bio+0x100/0x1b0 submit_bio_noacct_nocheck+0x230/0x49c blk_zone_wplug_bio_work+0x168/0x250 process_one_work+0x26c/0x65c worker_thread+0x33c/0x498 kthread+0x110/0x134 ret_from_fork+0x10/0x20
Call trace: __switch_to+0x230/0x410 __schedule+0xb08/0x1160 schedule+0x48/0xc8 blk_mq_freeze_queue_wait+0x78/0xb8 blk_mq_freeze_queue+0x90/0xa4 queue_attr_store+0x7c/0xf0 sysfs_kf_write+0x98/0xc8 kernfs_fop_write_iter+0x12c/0x1d4 vfs_write+0x340/0x3ac ksys_write+0x78/0xe8
Cc: Christoph Hellwig hch@lst.de Cc: Damien Le Moal dlemoal@kernel.org Cc: Yu Kuai yukuai1@huaweicloud.com Cc: Ming Lei ming.lei@redhat.com Cc: stable@vger.kernel.org Fixes: dd291d77cc90 ("block: Introduce zone write plugging") Signed-off-by: Bart Van Assche bvanassche@acm.org
Changes compared to v1: fixed a race condition. Call bio_zone_write_plugging() only before submitting the bio and not after it has been submitted.
block/blk-core.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c index b862c66018f2..713fb3865260 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -621,6 +621,13 @@ static inline blk_status_t blk_check_zone_append(struct request_queue *q, return BLK_STS_OK; } +/*
- Do not call bio_queue_enter() if the BIO_ZONE_WRITE_PLUGGING flag has been
- set because this causes blk_mq_freeze_queue() to deadlock if
- blk_zone_wplug_bio_work() submits a bio. Calling bio_queue_enter() for bios
- on the plug list is not necessary since a q_usage_counter reference is held
- while a bio is on the plug list.
- */
static void __submit_bio(struct bio *bio) { /* If plug is not used, add new plug here to cache nsecs time. */ @@ -633,8 +640,12 @@ static void __submit_bio(struct bio *bio) if (!bdev_test_flag(bio->bi_bdev, BD_HAS_SUBMIT_BIO)) { blk_mq_submit_bio(bio);
- } else if (likely(bio_queue_enter(bio) == 0)) {
- } else { struct gendisk *disk = bio->bi_bdev->bd_disk;
bool zwp = bio_zone_write_plugging(bio);if (unlikely(!zwp && bio_queue_enter(bio) != 0))goto finish_plug;@@ -643,9 +654,12 @@ static void __submit_bio(struct bio *bio) } else { disk->fops->submit_bio(bio); }
blk_queue_exit(disk->queue);
if (!zwp)blk_queue_exit(disk->queue);
This is pretty ugly, and I honestly absolutely hate how there's quite a bit of zoned_whatever sprinkling throughout the core code. What's the reason for not unplugging here, unaligned writes? Because you should presumable have the exact same issues on non-zoned devices if they have IO stuck in a plug (and doesn't get unplugged) while someone is waiting on a freeze.
A somewhat similar case was solved for IOPOLL and queue entering. That would be another thing to look at. Maybe a live enter could work if the plug itself pins it?