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authorNeilBrown <neilb@suse.com>2017-06-18 14:38:58 +1000
committerJens Axboe <axboe@kernel.dk>2017-06-18 12:40:59 -0600
commita8821f3f32bea173c7f9546b3b025898f0e09f58 (patch)
treed911354d3c07a5663256d5684d87f8d27435bdb6 /block/blk-merge.c
parent93b27e72904a9869e648c870bf0d04b124fda1c7 (diff)
downloadlinux-a8821f3f32bea173c7f9546b3b025898f0e09f58.tar.bz2
block: Improvements to bounce-buffer handling
Since commit 23688bf4f830 ("block: ensure to split after potentially bouncing a bio") blk_queue_bounce() is called *before* blk_queue_split(). This means that: 1/ the comments blk_queue_split() about bounce buffers are irrelevant, and 2/ a very large bio (more than BIO_MAX_PAGES) will no longer be split before it arrives at blk_queue_bounce(), leading to the possibility that bio_clone_bioset() will fail and a NULL will be dereferenced. Separately, blk_queue_bounce() shouldn't use fs_bio_set as the bio being copied could be from the same set, and this could lead to a deadlock. So: - allocate 2 private biosets for blk_queue_bounce, one for splitting enormous bios and one for cloning bios. - add code to split a bio that exceeds BIO_MAX_PAGES. - Fix up the comments in blk_queue_split() Credit-to: Ming Lei <tom.leiming@gmail.com> (suggested using single bio_for_each_segment loop) Reviewed-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: NeilBrown <neilb@suse.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-merge.c')
-rw-r--r--block/blk-merge.c14
1 files changed, 4 insertions, 10 deletions
diff --git a/block/blk-merge.c b/block/blk-merge.c
index d59074556703..51c84540d3bb 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -117,17 +117,11 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
* each holds at most BIO_MAX_PAGES bvecs because
* bio_clone() can fail to allocate big bvecs.
*
- * It should have been better to apply the limit per
- * request queue in which bio_clone() is involved,
- * instead of globally. The biggest blocker is the
- * bio_clone() in bio bounce.
+ * Those drivers which will need to use bio_clone()
+ * should tell us in some way. For now, impose the
+ * BIO_MAX_PAGES limit on all queues.
*
- * If bio is splitted by this reason, we should have
- * allowed to continue bios merging, but don't do
- * that now for making the change simple.
- *
- * TODO: deal with bio bounce's bio_clone() gracefully
- * and convert the global limit into per-queue limit.
+ * TODO: handle users of bio_clone() differently.
*/
if (bvecs++ >= BIO_MAX_PAGES)
goto split;