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

From: Dennis Zhou
Date: Sat Oct 20 2018 - 14:56:40 EST

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@xxxxxxxxxxxxxxxxxxxxxxx/
[2] https://lore.kernel.org/lkml/20180911184137.35897-1-dennisszhou@xxxxxxxxx/

This patchset contains the following 2 patches:

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(-)