* Re: [PATCH v1] block: make sure big bio is splitted into at most 256 bvecs
2016-04-06 3:43 [PATCH v1] block: make sure big bio is splitted into at most 256 bvecs Ming Lei
@ 2016-04-06 3:46 ` Kent Overstreet
2016-08-11 6:33 ` [PATCH v2] " Eric Wheeler
1 sibling, 0 replies; 6+ messages in thread
From: Kent Overstreet @ 2016-04-06 3:46 UTC (permalink / raw)
To: Ming Lei
Cc: Jens Axboe, linux-kernel, linux-block, Christoph Hellwig,
Eric Wheeler, Sebastian Roesner, 4.3+,
Shaohua Li
On Wed, Apr 06, 2016 at 11:43:32AM +0800, Ming Lei wrote:
> After arbitrary bio size is supported, 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 for safety reason, such
> as bio_clone().
>
> This patch fixes the following kernel crash:
>
> > [ 172.660142] BUG: unable to handle kernel NULL pointer dereference at 0000000000000028
> > [ 172.660229] IP: [<ffffffff811e53b4>] bio_trim+0xf/0x2a
> > [ 172.660289] PGD 7faf3e067 PUD 7f9279067 PMD 0
> > [ 172.660399] Oops: 0000 [#1] SMP
> > [...]
> > [ 172.664780] Call Trace:
> > [ 172.664813] [<ffffffffa007f3be>] ? raid1_make_request+0x2e8/0xad7 [raid1]
> > [ 172.664846] [<ffffffff811f07da>] ? blk_queue_split+0x377/0x3d4
> > [ 172.664880] [<ffffffffa005fb5f>] ? md_make_request+0xf6/0x1e9 [md_mod]
> > [ 172.664912] [<ffffffff811eb860>] ? generic_make_request+0xb5/0x155
> > [ 172.664947] [<ffffffffa0445c89>] ? prio_io+0x85/0x95 [bcache]
> > [ 172.664981] [<ffffffffa0448252>] ? register_cache_set+0x355/0x8d0 [bcache]
> > [ 172.665016] [<ffffffffa04497d3>] ? register_bcache+0x1006/0x1174 [bcache]
>
> Fixes: 54efd50(block: make generic_make_request handle arbitrarily sized bios)
> Reported-by: Sebastian Roesner <sroesner-kernelorg@roesner-online.de>
> Reported-by: Eric Wheeler <bcache@lists.ewheeler.net>
> Cc: stable@vger.kernel.org (4.3+)
> Cc: Shaohua Li <shli@fb.com>
> Cc: Kent Overstreet <kent.overstreet@gmail.com>
> Signed-off-by: Ming Lei <ming.lei@canonical.com>
That'll work
Acked-by: Kent Overstreet <kent.overstreet@gmail.com>
> ---
> V1:
> - Kent pointed out that using max io size can't cover
> the case of non-full bvecs/pages
>
> The issue can be reproduced by the following approach:
> - create one raid1 over two virtio-blk
> - build bcache device over the above raid1 and another cache device
> and bucket size is set 2Mbytes
> - set cache mode as writeback
> - run random write over ext4 on the bcache device
> - then the crash can be triggered
>
> block/blk-merge.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 2613531..7b96471 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -94,8 +94,10 @@ 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) {
> + bvecs++;
> /*
> * If the queue doesn't support SG gaps and adding this
> * offset would create a gap, disallow it.
> @@ -103,6 +105,23 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
> if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
> goto split;
>
> + /*
> + * 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
> + * bio_clone() in bio bounce.
> + *
> + * 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 (sectors + (bv.bv_len >> 9) > max_sectors) {
> /*
> * Consider this a new segment if we're splitting in
> --
> 1.9.1
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] block: make sure big bio is splitted into at most 256 bvecs
2016-04-06 3:43 [PATCH v1] block: make sure big bio is splitted into at most 256 bvecs Ming Lei
2016-04-06 3:46 ` Kent Overstreet
@ 2016-08-11 6:33 ` Eric Wheeler
2016-08-11 14:02 ` Christoph Hellwig
1 sibling, 1 reply; 6+ messages in thread
From: Eric Wheeler @ 2016-08-11 6:33 UTC (permalink / raw)
To: Ming Lei
Cc: Jens Axboe, linux-kernel, linux-block, linux-bcache, linux-raid,
kent.overstreet, Christoph Hellwig, Sebastian Roesner, 4.3+,
Shaohua Li
On Fri, 10 Jun 2016, Christoph Hellwig wrote:
> On Wed, 6 Apr 2016, Ming Lei wrote:
> >
> > After arbitrary bio size is supported, 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 for safety reason, such
> > as bio_clone().
> >
> > This patch fixes the following kernel crash:
> > [ 172.664813] [<ffffffffa007f3be>] ? raid1_make_request+0x2e8/0xad7 [raid1]
> > [ 172.664846] [<ffffffff811f07da>] ? blk_queue_split+0x377/0x3d4
> > [ 172.664880] [<ffffffffa005fb5f>] ? md_make_request+0xf6/0x1e9 [md_mod]
> > [ 172.664912] [<ffffffff811eb860>] ? generic_make_request+0xb5/0x155
> > [ 172.664947] [<ffffffffa0445c89>] ? prio_io+0x85/0x95 [bcache]
>
> The fixup to allow bio_clone support a larger size is the same one as to
> allow everyone else submitting larger bios: increase BIO_MAX_PAGES and
> create the required mempools to back that new larger size. Or just go
> for multipage biovecs..
Hi Christoph, Ming, everyone:
I'm hoping you can help me get this off of a list of stability fixes
related to changes around Linux 4.3. Ming's patch [1] is known to fix an
issue when a bio with bi_vcnt > BIO_MAX_PAGES is passed to
generic_make_request and later hits bio_clone. (Note that bi_vcnt can't
be trusted since immutable biovecs and needs to be re-counted unless you
own the bio, which Ming's patch does.)
The diffstat, 22 lines of which are commentary,
seems relatively minor and would land in stable for v4.3+:
block/blk-merge.c | 35 ++++++++++++++++++++++++++++++++---
I'm not sure I understood Christoph's suggestion; BIO_MAX_PAGES is a
static #define and we don't know what the the bi_vcnt from an arbitrary
driver might be. Wouldn't increasing BIO_MAX_PAGES just push the problem
further out into the future when bi_vcnt might again exceed BIO_MAX_PAGES?
Perhaps you could elaborate if I have misunderstood. Are you suggesting
that no driver should call generic_make_request when bi_vcnt > BIO_MAX_PAGES?
--
Eric Wheeler
[1] https://patchwork.kernel.org/patch/9169483/
Pasted below:
After arbitrary bio size is supported, 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 for safety reason, such
as bio_clone().
This patch fixes the following kernel crash:
> [ 172.660142] BUG: unable to handle kernel NULL pointer dereference at 0000000000000028
> [ 172.660229] IP: [<ffffffff811e53b4>] bio_trim+0xf/0x2a
> [ 172.660289] PGD 7faf3e067 PUD 7f9279067 PMD 0
> [ 172.660399] Oops: 0000 [#1] SMP
> [...]
> [ 172.664780] Call Trace:
> [ 172.664813] [<ffffffffa007f3be>] ? raid1_make_request+0x2e8/0xad7 [raid1]
> [ 172.664846] [<ffffffff811f07da>] ? blk_queue_split+0x377/0x3d4
> [ 172.664880] [<ffffffffa005fb5f>] ? md_make_request+0xf6/0x1e9 [md_mod]
> [ 172.664912] [<ffffffff811eb860>] ? generic_make_request+0xb5/0x155
> [ 172.664947] [<ffffffffa0445c89>] ? prio_io+0x85/0x95 [bcache]
> [ 172.664981] [<ffffffffa0448252>] ? register_cache_set+0x355/0x8d0 [bcache]
> [ 172.665016] [<ffffffffa04497d3>] ? register_bcache+0x1006/0x1174 [bcache]
The issue can be reproduced by the following steps:
- create one raid1 over two virtio-blk
- build bcache device over the above raid1 and another cache device
and bucket size is set as 2Mbytes
- set cache mode as writeback
- run random write over ext4 on the bcache device
Fixes: 54efd50(block: make generic_make_request handle arbitrarily sized bios)
Reported-by: Sebastian Roesner <sroesner-kernelorg@roesner-online.de>
Reported-by: Eric Wheeler <bcache@lists.ewheeler.net>
Cc: stable@vger.kernel.org (4.3+)
Cc: Shaohua Li <shli@fb.com>
Acked-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
V2:
- don't mark as REQ_NOMERGE in case the bio is splitted
for reaching the limit of bvecs count
V1:
- Kent pointed out that using max io size can't cover
the case of non-full bvecs/pages
block/blk-merge.c | 35 ++++++++++++++++++++++++++++++++---
1 file changed, 32 insertions(+), 3 deletions(-)
diff --git a/block/blk-merge.c b/block/blk-merge.c
index c265348..839529b 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -85,7 +85,8 @@ static inline unsigned get_max_io_size(struct request_queue *q,
static struct bio *blk_bio_segment_split(struct request_queue *q,
struct bio *bio,
struct bio_set *bs,
- unsigned *segs)
+ unsigned *segs,
+ bool *no_merge)
{
struct bio_vec bv, bvprv, *bvprvp = NULL;
struct bvec_iter iter;
@@ -94,9 +95,34 @@ 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;
+
+ *no_merge = true;
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
+ * bio_clone() in bio bounce.
+ *
+ * If bio is splitted by this reason, we should allow
+ * to continue bios merging.
+ *
+ * TODO: deal with bio bounce's bio_clone() gracefully
+ * and convert the global limit into per-queue limit.
+ */
+ if (bvecs++ >= BIO_MAX_PAGES) {
+ *no_merge = false;
+ goto split;
+ }
+
+ /*
* If the queue doesn't support SG gaps and adding this
* offset would create a gap, disallow it.
*/
@@ -171,13 +197,15 @@ void blk_queue_split(struct request_queue *q, struct bio **bio,
{
struct bio *split, *res;
unsigned nsegs;
+ bool no_merge_for_split = true;
if (bio_op(*bio) == REQ_OP_DISCARD)
split = blk_bio_discard_split(q, *bio, bs, &nsegs);
else if (bio_op(*bio) == REQ_OP_WRITE_SAME)
split = blk_bio_write_same_split(q, *bio, bs, &nsegs);
else
- split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs);
+ split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs,
+ &no_merge_for_split);
/* physical segments can be figured out during splitting */
res = split ? split : *bio;
@@ -186,7 +214,8 @@ void blk_queue_split(struct request_queue *q, struct bio **bio,
if (split) {
/* there isn't chance to merge the splitted bio */
- split->bi_rw |= REQ_NOMERGE;
+ if (no_merge_for_split)
+ split->bi_rw |= REQ_NOMERGE;
bio_chain(split, *bio);
trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
^ permalink raw reply related [flat|nested] 6+ messages in thread