[PATCH] blk-merge: fix blk_recount_segments

Ming Lei
2014-09-02T15:03:42Z

QUEUE_FLAG_NO_SG_MERGE is set at default for blk-mq devices,
so bio->bi_phys_segment computed may be bigger than
queue_max_segments(q) for blk-mq devices, then drivers will
fail to handle the case, for example, BUG_ON() in
virtio_queue_rq() can be triggerd for virtio-blk:

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1359146

This patch fixes the issue by ignoring the QUEUE_FLAG_NO_SG_MERGE
flag if the computed bio->bi_phys_segment is bigger than
queue_max_segments(q), and the regression is caused by commit
05f1dd53152173(block: add queue flag for disabling SG merging).

Reported-by: Kick In <pierre-andre.morey@canonical.com>
Tested-by: Chris J Arges <chris.j.arges@canonical.com>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
block/blk-merge.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 5453583..7788179 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -10,10 +10,11 @@
#include "blk.h"

static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
- struct bio *bio)
+ struct bio *bio,
+ bool no_sg_merge)
{
struct bio_vec bv, bvprv = { NULL };
- int cluster, high, highprv = 1, no_sg_merge;
+ int cluster, high, highprv = 1;
unsigned int seg_size, nr_phys_segs;
struct bio *fbio, *bbio;
struct bvec_iter iter;
@@ -35,7 +36,6 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
cluster = blk_queue_cluster(q);
seg_size = 0;
nr_phys_segs = 0;
- no_sg_merge = test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags);
high = 0;
for_each_bio(bio) {
bio_for_each_segment(bv, bio, iter) {
@@ -88,18 +88,23 @@ new_segment:

void blk_recalc_rq_segments(struct request *rq)
{
- rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio);
+ bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
+ &rq->q->queue_flags);
+
+ rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
+ no_sg_merge);
}

void blk_recount_segments(struct request_queue *q, struct bio *bio)
{
- if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags))
+ if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
+ bio->bi_vcnt < queue_max_segments(q))
bio->bi_phys_segments = bio->bi_vcnt;
else {
struct bio *nxt = bio->bi_next;

bio->bi_next = NULL;
- bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio);
+ bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
bio->bi_next = nxt;
}

--
1.7.9.5