Commit a8821f3f authored by NeilBrown's avatar NeilBrown Committed by Jens Axboe

block: Improvements to bounce-buffer handling

Since commit 23688bf4 ("block: ensure to split after potentially
bouncing a bio") blk_queue_bounce() is called *before*
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

 - 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 <> (suggested using single bio_for_each_segment loop)
Reviewed-by: default avatarMing Lei <>
Reviewed-by: default avatarChristoph Hellwig <>
Signed-off-by: default avatarNeilBrown <>
Signed-off-by: default avatarJens Axboe <>
parent 93b27e72
......@@ -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;
......@@ -26,6 +26,7 @@
#define POOL_SIZE 64
#define ISA_POOL_SIZE 16
struct bio_set *bounce_bio_set, *bounce_bio_split;
static mempool_t *page_pool, *isa_page_pool;
......@@ -40,6 +41,14 @@ static __init int init_emergency_pool(void)
pr_info("pool size: %d pages\n", POOL_SIZE);
bounce_bio_set = bioset_create(BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
if (bioset_integrity_create(bounce_bio_set, BIO_POOL_SIZE))
bounce_bio_split = bioset_create(BIO_POOL_SIZE, 0, 0);
return 0;
......@@ -186,15 +195,26 @@ static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
int rw = bio_data_dir(*bio_orig);
struct bio_vec *to, from;
struct bvec_iter iter;
unsigned i;
unsigned i = 0;
bool bounce = false;
int sectors = 0;
bio_for_each_segment(from, *bio_orig, iter)
bio_for_each_segment(from, *bio_orig, iter) {
if (i++ < BIO_MAX_PAGES)
sectors += from.bv_len >> 9;
if (page_to_pfn(from.bv_page) > queue_bounce_pfn(q))
goto bounce;
bounce = true;
if (!bounce)
bio = bio_clone_bioset(*bio_orig, GFP_NOIO, fs_bio_set);
if (sectors < bio_sectors(*bio_orig)) {
bio = bio_split(*bio_orig, sectors, GFP_NOIO, bounce_bio_split);
bio_chain(bio, *bio_orig);
*bio_orig = bio;
bio = bio_clone_bioset(*bio_orig, GFP_NOIO, bounce_bio_set);
bio_for_each_segment_all(to, bio, i) {
struct page *page = to->bv_page;
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment