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[0/2] block: fixes for always associate blkg

Message ID 20181020185612.51587-1-dennis@kernel.org (mailing list archive)
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Series block: fixes for always associate blkg | expand

Message

Dennis Zhou Oct. 20, 2018, 6:56 p.m. UTC 
Hi everyone,

It was reported in [1] that blk_get_rl() cleanup patch was causing a
null pointer dereference. After some back and forth debugging with
Valdis, it turns out I wasn't properly handling association with
recursive calls to make_request().

Another issue was identified with the blk_get_rl() update as it is
possible under certain circumstances that a blkg cannot be allocated
when called in blk_get_rl(). This could result in the blkcg_root being
returned. However, the blkcg_root is a special case where all blkgs
share the request_queue's request_list.

The original series can be found at [2].

[1] https://lore.kernel.org/lkml/13987.1539646128@turing-police.cc.vt.edu/
[2] https://lore.kernel.org/lkml/20180911184137.35897-1-dennisszhou@gmail.com/

This patchset contains the following 2 patches:
  0001-blkcg-fix-edge-case-for-blk_get_rl-under-memory-pres.patch
  0002-blkcg-reassociate-bios-when-make_request-is-called-r.patch

0001 addresses an edge case where a blkg cannot be created and can
possibly return a blkg associated with the blkcg_root. 0002 fixes the
stale association when make_request() is called recursively.

This patchset is on top of axboe#for-4.20/block bbc152825afc.

diffstats below:

Dennis Zhou (2):
  blkcg: fix edge case for blk_get_rl() under memory pressure
  blkcg: reassociate bios when make_request() is called recursively

 block/bio.c                | 20 ++++++++++++++++++++
 block/blk-core.c           |  1 +
 include/linux/bio.h        |  3 +++
 include/linux/blk-cgroup.h |  2 +-
 4 files changed, 25 insertions(+), 1 deletion(-)

Thanks,
Dennis

Comments

Jens Axboe Oct. 20, 2018, 9:40 p.m. UTC | #1 
On 10/20/18 12:56 PM, Dennis Zhou wrote:
> Hi everyone,
> 
> It was reported in [1] that blk_get_rl() cleanup patch was causing a
> null pointer dereference. After some back and forth debugging with
> Valdis, it turns out I wasn't properly handling association with
> recursive calls to make_request().
> 
> Another issue was identified with the blk_get_rl() update as it is
> possible under certain circumstances that a blkg cannot be allocated
> when called in blk_get_rl(). This could result in the blkcg_root being
> returned. However, the blkcg_root is a special case where all blkgs
> share the request_queue's request_list.
> 
> The original series can be found at [2].
> 
> [1] https://lore.kernel.org/lkml/13987.1539646128@turing-police.cc.vt.edu/
> [2] https://lore.kernel.org/lkml/20180911184137.35897-1-dennisszhou@gmail.com/
> 
> This patchset contains the following 2 patches:
>   0001-blkcg-fix-edge-case-for-blk_get_rl-under-memory-pres.patch
>   0002-blkcg-reassociate-bios-when-make_request-is-called-r.patch
> 
> 0001 addresses an edge case where a blkg cannot be created and can
> possibly return a blkg associated with the blkcg_root. 0002 fixes the
> stale association when make_request() is called recursively.

Thanks Dennis, applied.