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 <ax...@kernel.dk>
Cc: Maurizio Lombardi <mlomb...@redhat.com>
Cc: Dongsu Park <dongsu.p...@profitbricks.com>
Cc: Christoph Hellwig <h...@lst.de>
Cc: Kent Overstreet <k...@daterainc.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Reported-by: Jet Chen <jet.c...@intel.com>
Tested-by: Jet Chen <jet.c...@intel.com>
Signed-off-by: Ming Lei <ming....@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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