linux-toradex.git/block/blk-merge.c, branch v4.4.104

block: make sure a big bio is split into at most 256 bvecs

2016-09-15T06:27:51+00:00

commit 4d70dca4eadf2f95abe389116ac02b8439c2d16c upstream.

After arbitrary bio size was introduced, 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: [] bio_trim+0xf/0x2a
> [  172.660289] PGD 7faf3e067 PUD 7f9279067 PMD 0
> [  172.660399] Oops: 0000 [#1] SMP
> [...]
> [  172.664780] Call Trace:
> [  172.664813]  [] ? raid1_make_request+0x2e8/0xad7 [raid1]
> [  172.664846]  [] ? blk_queue_split+0x377/0x3d4
> [  172.664880]  [] ? md_make_request+0xf6/0x1e9 [md_mod]
> [  172.664912]  [] ? generic_make_request+0xb5/0x155
> [  172.664947]  [] ? prio_io+0x85/0x95 [bcache]
> [  172.664981]  [] ? register_cache_set+0x355/0x8d0 [bcache]
> [  172.665016]  [] ? 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 
Reported-by: Eric Wheeler 
Cc: Shaohua Li 
Acked-by: Kent Overstreet 
Signed-off-by: Ming Lei 
Signed-off-by: Jens Axboe 
Signed-off-by: Greg Kroah-Hartman

block: fix bio splitting on max sectors

2016-02-17T20:30:56+00:00

commit d0e5fbb01a67e400e82fefe4896ea40c6447ab98 upstream.

After commit e36f62042880(block: split bios to maxpossible length),
bio can be splitted in the middle of a vector entry, then it
is easy to split out one bio which size isn't aligned with block
size, especially when the block size is bigger than 512.

This patch fixes the issue by making the max io size aligned
to logical block size.

Fixes: e36f62042880(block: split bios to maxpossible length)
Reported-by: Stefan Haberland 
Cc: Keith Busch 
Suggested-by: Linus Torvalds 
Signed-off-by: Ming Lei 
Signed-off-by: Jens Axboe 
Signed-off-by: Greg Kroah-Hartman

block: split bios to max possible length

2016-02-17T20:30:55+00:00

commit e36f6204288088fda50d1c84830340ccb70f85ff upstream.

This splits bio in the middle of a vector to form the largest possible
bio at the h/w's desired alignment, and guarantees the bio being split
will have some data.

The criteria for splitting is changed from the max sectors to the h/w's
optimal sector alignment if it is provided. For h/w that advertise their
block storage's underlying chunk size, it's a big performance win to not
submit commands that cross them. If sector alignment is not provided,
this patch uses the max sectors as before.

This addresses the performance issue commit d380561113 attempted to
fix, but was reverted due to splitting logic error.

Signed-off-by: Keith Busch 
Cc: Jens Axboe 
Cc: Ming Lei 
Cc: Kent Overstreet 
Signed-off-by: Jens Axboe 
Signed-off-by: Greg Kroah-Hartman

Revert "block: Split bios on chunk boundaries"

2016-01-08T16:00:29+00:00

This reverts commit d3805611130af9b911e908af9f67a3f64f4f0914.

If we end up splitting on the first segment, we don't adjust
the sector count. That results in hitting a BUG() with attempting
to split 0 sectors.

As this is just a performance issue and not a regression since
4.3 release, let's just rever this change. That gives us more
time to test a real fix for 4.5, which would be marked for
stable anyway.

block: Split bios on chunk boundaries

2015-12-23T00:19:25+00:00

For h/w that advertise their block storage's underlying chunk size, it's
a big performance win to not submit commands that cross them. This patch
uses that criteria if it is provided. If it is not provided, this patch
uses the max sectors as before.

Signed-off-by: Keith Busch 
Signed-off-by: Jens Axboe

blk-merge: fix computing bio->bi_seg_front_size in case of single segment

2015-11-30T20:02:36+00:00

When bio has only one physical segment, we should set bio's
bi_seg_front_size as the real(final) size of the single segment.

Fixes: 02e707424c2ea(blk-merge: fix blk_bio_segment_split)
Reported-by: Markus Trippelsdorf 
Tested-by: Markus Trippelsdorf 
Signed-off-by: Ming Lei 
Signed-off-by: Jens Axboe

blk-merge: warn if figured out segment number is bigger than nr_phys_segments

2015-11-24T03:16:55+00:00

We had seen lots of reports of this kind issue, so add one
warnning in blk-merge, then it can be triggered easily and
avoid to depend on warning/bug from drivers.

Signed-off-by: Ming Lei 
Signed-off-by: Jens Axboe

blk-merge: fix blk_bio_segment_split

2015-11-24T03:16:53+00:00

Commit bdced438acd83a(block: setup bi_phys_segments after
splitting) introduces function of computing bio->bi_phys_segments
during bio splitting.

Unfortunately both bio->bi_seg_front_size and bio->bi_seg_back_size
arn't computed, so too many physical segments may be obtained
for one request since both the two are used to check if one segment
across two bios can be possible.

This patch fixes the issue by computing the two variables in
blk_bio_segment_split().

Fixes: bdced438acd83a(block: setup bi_phys_segments after splitting)
Reported-by: Michael Ellerman 
Reported-by: Mark Salter 
Tested-by: Laurent Dufour 
Tested-by: Mark Salter 
Signed-off-by: Ming Lei 
Signed-off-by: Jens Axboe

block: fix segment split

2015-11-24T03:16:51+00:00

Inside blk_bio_segment_split(), previous bvec pointer(bvprvp)
always points to the iterator local variable, which is obviously
wrong, so fix it by pointing to the local variable of 'bvprv'.

Fixes: 5014c311baa2b(block: fix bogus compiler warnings in blk-merge.c)
Cc: stable@kernel.org #4.3
Reported-by: Michael Ellerman 
Reported-by: Mark Salter 
Tested-by: Laurent Dufour 
Tested-by: Mark Salter 
Signed-off-by: Ming Lei 
Signed-off-by: Jens Axboe

block: avoid to merge splitted bio

2015-10-21T21:00:51+00:00

The splitted bio has been already too fat to merge, so mark it
as NOMERGE.

Reviewed-by: Jeff Moyer 
Signed-off-by: Ming Lei 
Signed-off-by: Jens Axboe