[PATCH 0/4 v5] bfq: Avoid use-after-free when moving processes between cgroups

[Jan Kara <jack@suse.cz>]

Hello,

here is the fifth version of my patches to fix use-after-free issues in BFQ
when processes with merged queues get moved to different cgroups. The patches
have survived some beating in my test VM, but so far I fail to reproduce the
original KASAN reports so testing from people who can reproduce them is most
welcome. Kuai, can you please give these patches a run in your setup? Thanks
a lot for your help with fixing this!

Changes since v4:
* Even more aggressive splitting of merged bfq queues to avoid problems with
  long merge chains.

Changes since v3:
* Changed handling of bfq group move to handle the case when target of the
  merge has moved.

Changes since v2:
* Improved handling of bfq queue splitting on move between cgroups
* Removed broken change to bfq_put_cooperator()

Changes since v1:
* Added fix for bfq_put_cooperator()
* Added fix to handle move between cgroups in bfq_merge_bio()

								Honza
Previous versions:
Link: http://lore.kernel.org/r/20211223171425.3551-1-jack@suse.cz # v1
Link: http://lore.kernel.org/r/20220105143037.20542-1-jack@suse.cz # v2
Link: http://lore.kernel.org/r/20220112113529.6355-1-jack@suse.cz # v3
Link: http://lore.kernel.org/r/20220114164215.28972-1-jack@suse.cz # v4