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Commit a8821f3f authored by NeilBrown's avatar NeilBrown Committed by Jens Axboe
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block: Improvements to bounce-buffer handling 



Since commit 23688bf4 ("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: default avatarMing Lei <ming.lei@redhat.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarNeilBrown <neilb@suse.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 93b27e72

block/blk-merge.c

+4 −10
Original line number Diff line number Diff line
@@ -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;

block/bounce.c

+26 −6
Original line number Diff line number Diff line
@@ -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;



#if defined(CONFIG_HIGHMEM) || defined(CONFIG_NEED_BOUNCE_POOL)
@@ -40,6 +41,14 @@ static __init int init_emergency_pool(void) 
	BUG_ON(!page_pool);

	pr_info("pool size: %d pages\n", POOL_SIZE);



	bounce_bio_set = bioset_create(BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);

	BUG_ON(!bounce_bio_set);

	if (bioset_integrity_create(bounce_bio_set, BIO_POOL_SIZE))

		BUG_ON(1);



	bounce_bio_split = bioset_create(BIO_POOL_SIZE, 0, 0);

	BUG_ON(!bounce_bio_split);



	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)

		return;

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);

		generic_make_request(*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;