Messages in this thread Patch in this message | | | From | Ming Lei <> | Subject | [PATCH] block/bio.c: update bi_iter.bi_size before recounting segments | Date | Thu, 29 May 2014 15:59:40 +0800 |
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The patch of "bio: modify __bio_add_page() to accept pages that don't start a new segment" changes the way for adding one page to bio:
- previously by adding page after checking successfully - now by trying to add page and recover if it fails
Unfortunately the patch forgets to update bio->bi_iter.bi_size before trying to add page, then the last vector for holding the added page may not be covered if recouning segments is needed, so bio->bi_phys_segments may become not consistent with the actual bio page buffers after the page is added successfully to the bio(after bi_iter.bi_size is added by 'len')
Suppose the page in the last vector can't be merged to bio, tragedy will happen when __bio_add_page() is called to add another page:
- blk_recount_segments() is called and the actual segments get figured out correctly
- the actual segments may become queue_max_segments(q) plus one in failure path
- driver will find the segment count is too big to handle.
The patch fixes the virtio-blk oops bug reported from Jet Chen in below link:
http://marc.info/?l=linux-kernel&m=140113053817095&w=2
Cc: Jens Axboe <axboe@kernel.dk> Cc: Maurizio Lombardi <mlombard@redhat.com> Cc: Dongsu Park <dongsu.park@profitbricks.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Kent Overstreet <kmo@daterainc.com> Cc: Andrew Morton <akpm@linux-foundation.org> Reported-by: Jet Chen <jet.chen@intel.com> Tested-by: Jet Chen <jet.chen@intel.com> Signed-off-by: Ming Lei <ming.lei@canonical.com> --- Andrew, could you put the patch in your -mm tree because the previous two patches were routed from your tree?
block/bio.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/block/bio.c b/block/bio.c index 0443694..f9bae56 100644 --- a/block/bio.c +++ b/block/bio.c @@ -744,6 +744,7 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page } } + bio->bi_iter.bi_size += len; goto done; } } @@ -761,6 +762,7 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page bvec->bv_offset = offset; bio->bi_vcnt++; bio->bi_phys_segments++; + bio->bi_iter.bi_size += len; /* * Perform a recount if the number of segments is greater @@ -802,7 +804,6 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page bio->bi_flags &= ~(1 << BIO_SEG_VALID); done: - bio->bi_iter.bi_size += len; return len; failed: @@ -810,6 +811,7 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page bvec->bv_len = 0; bvec->bv_offset = 0; bio->bi_vcnt--; + bio->bi_iter.bi_size -= len; blk_recount_segments(q, bio); return 0; } -- 1.7.9.5
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