[PATCH 03/11] block: check BLK_FEAT_POLL under q_usage_count

Christoph Hellwig
2025-01-10T05:47:37Z

Otherwise feature reconfiguration can race with I/O submission.

Also drop the bio_clear_polled in the error path, as the flag does not
matter for instant error completions, it is a left over from when we
allowed polled I/O to proceed unpolled in this case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
---
block/blk-core.c | 22 ++++++++++++----------
block/blk-mq.c | 12 ++++++++++--
2 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 666efe8fa202..6309b3f5a89d 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -629,8 +629,14 @@ static void __submit_bio(struct bio *bio)
blk_mq_submit_bio(bio);
} else if (likely(bio_queue_enter(bio) == 0)) {
struct gendisk *disk = bio->bi_bdev->bd_disk;
-
- disk->fops->submit_bio(bio);
+
+ if ((bio->bi_opf & REQ_POLLED) &&
+ !(disk->queue->limits.features & BLK_FEAT_POLL)) {
+ bio->bi_status = BLK_STS_NOTSUPP;
+ bio_endio(bio);
+ } else {
+ disk->fops->submit_bio(bio);
+ }
blk_queue_exit(disk->queue);
}

@@ -805,12 +811,6 @@ void submit_bio_noacct(struct bio *bio)
}
}

- if (!(q->limits.features & BLK_FEAT_POLL) &&
- (bio->bi_opf & REQ_POLLED)) {
- bio_clear_polled(bio);
- goto not_supported;
- }
-
switch (bio_op(bio)) {
case REQ_OP_READ:
break;
@@ -935,7 +935,7 @@ int bio_poll(struct bio *bio, struct io_comp_batch *iob, unsigned int flags)
return 0;

q = bdev_get_queue(bdev);
- if (cookie == BLK_QC_T_NONE || !(q->limits.features & BLK_FEAT_POLL))
+ if (cookie == BLK_QC_T_NONE)
return 0;

blk_flush_plug(current->plug, false);
@@ -951,7 +951,9 @@ int bio_poll(struct bio *bio, struct io_comp_batch *iob, unsigned int flags)
*/
if (!percpu_ref_tryget(&q->q_usage_counter))
return 0;
- if (queue_is_mq(q)) {
+ if (!(q->limits.features & BLK_FEAT_POLL)) {
+ ret = 0;
+ } else if (queue_is_mq(q)) {
ret = blk_mq_poll(q, cookie, iob, flags);
} else {
struct gendisk *disk = q->disk;
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 2e6132f778fd..02c9232a8fff 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3096,14 +3096,22 @@ void blk_mq_submit_bio(struct bio *bio)
}

/*
- * Device reconfiguration may change logical block size, so alignment
- * check has to be done with queue usage counter held
+ * Device reconfiguration may change logical block size or reduce the
+ * number of poll queues, so the checks for alignment and poll support
+ * have to be done with queue usage counter held.
*/
if (unlikely(bio_unaligned(bio, q))) {
bio_io_error(bio);
goto queue_exit;
}

+ if ((bio->bi_opf & REQ_POLLED) &&
+ !(q->limits.features & BLK_FEAT_POLL)) {
+ bio->bi_status = BLK_STS_NOTSUPP;
+ bio_endio(bio);
+ goto queue_exit;
+ }
+
bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);
if (!bio)
goto queue_exit;
--
2.45.2