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-rw-r--r--block/blk-merge.c22
1 files changed, 22 insertions, 0 deletions
diff --git a/block/blk-merge.c b/block/blk-merge.c
index b966db8f3556..7225511cf0b4 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -92,9 +92,31 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
bool do_split = true;
struct bio *new = NULL;
const unsigned max_sectors = get_max_io_size(q, bio);
+ unsigned bvecs = 0;
bio_for_each_segment(bv, bio, iter) {
/*
+ * With arbitrary bio size, the incoming bio may be very
+ * big. We have to split the bio into small bios so that
+ * 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.
+ *
+ * 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.
+ */
+ if (bvecs++ >= BIO_MAX_PAGES)
+ goto split;
+
+ /*
* If the queue doesn't support SG gaps and adding this
* offset would create a gap, disallow it.
*/