| Message ID | 149369654475.5146.215368176129979588.stgit@noble (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Looks fine,
Reviewed-by: Christoph Hellwig <hch@lst.de>
although I think we really should kill off the block level bouncing
rather sooner than later.
On Tue, May 02, 2017 at 01:42:24PM +1000, NeilBrown wrote: > 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) > Signed-off-by: NeilBrown <neilb@suse.com> > --- > block/blk-merge.c | 14 ++++---------- > block/bounce.c | 32 ++++++++++++++++++++++++++------ > 2 files changed, 30 insertions(+), 16 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; > diff --git a/block/bounce.c b/block/bounce.c > index 1cb5dd3a5da1..087ecc2dc66c 100644 > --- a/block/bounce.c > +++ b/block/bounce.c > @@ -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; > > - 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; Reviewed-by: Ming Lei <ming.lei@redhat.com> Thanks, Ming
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; diff --git a/block/bounce.c b/block/bounce.c index 1cb5dd3a5da1..087ecc2dc66c 100644 --- a/block/bounce.c +++ b/block/bounce.c @@ -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; - 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;
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) Signed-off-by: NeilBrown <neilb@suse.com> --- block/blk-merge.c | 14 ++++---------- block/bounce.c | 32 ++++++++++++++++++++++++++------ 2 files changed, 30 insertions(+), 16 deletions(-)