From b21e11c5c8311b8bf6923ff29d57f2a5f997e939 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Tue, 2 Apr 2019 10:26:44 +0800 Subject: block: fix build warning in merging bvecs Commit f6970f83ef79 ("block: don't check if adjacent bvecs in one bio can be mergeable") changes bvec merge by only considering two bvecs from different bios. However, if the former bio doesn't inlcude any io bvec, then the following warning may be triggered: warning: ‘bvec.bv_offset’ may be used uninitialized in this function [-Wmaybe-uninitialized] In practice, it shouldn't be triggered. Fixes it by adding check on former bio, the check shouldn't add any cost given 'bio->bi_iter' can be hit in cache. Reported-by: Jens Axboe Fixes: f6970f83ef79 ("block: don't check if adjacent bvecs in one bio can be mergeable") Signed-off-by: Ming Lei Signed-off-by: Jens Axboe --- block/blk-merge.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) (limited to 'block/blk-merge.c') diff --git a/block/blk-merge.c b/block/blk-merge.c index 8f96d683b577..895795cdb145 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -353,7 +353,7 @@ EXPORT_SYMBOL(blk_queue_split); static unsigned int __blk_recalc_rq_segments(struct request_queue *q, struct bio *bio) { - struct bio_vec bv, bvprv = { NULL }; + struct bio_vec uninitialized_var(bv), bvprv = { NULL }; unsigned int seg_size, nr_phys_segs; unsigned front_seg_size; struct bio *fbio, *bbio; @@ -400,8 +400,10 @@ new_segment: new_bio = false; } bbio = bio; - bvprv = bv; - new_bio = true; + if (likely(bio->bi_iter.bi_size)) { + bvprv = bv; + new_bio = true; + } } fbio->bi_seg_front_size = front_seg_size; @@ -527,7 +529,7 @@ static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio, struct scatterlist *sglist, struct scatterlist **sg) { - struct bio_vec bvec, bvprv = { NULL }; + struct bio_vec uninitialized_var(bvec), bvprv = { NULL }; struct bvec_iter iter; int nsegs = 0; bool new_bio = false; @@ -550,8 +552,10 @@ static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio, next_bvec: new_bio = false; } - bvprv = bvec; - new_bio = true; + if (likely(bio->bi_iter.bi_size)) { + bvprv = bvec; + new_bio = true; + } } return nsegs; -- cgit v1.2.3