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xfs: fix cpu hotplug mess [v2]

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Ritesh and Eric separately reported crashes in XFS's hook function for
 CPU hot remove if the remove event races with a filesystem being
 mounted.  I also noticed via generic/650 that once in a while the log
 will shut down over an apparent overrun of a transaction reservation;
 this turned out to be due to CIL percpu list aggregation failing to pick
 up the percpu list items from a dying CPU.
 
 Either way, the solution here is to eliminate the need for a CPU dying
 hook by using a private cpumask to track which CPUs have added to their
 percpu lists directly, and iterating with that mask.  This fixes the log
 problems and (I think) solves a theoretical UAF bug in the inodegc code
 too.
 
 v2: fix a few put_cpu uses, add necessary memory barriers, and use
     atomic cpumask operations
 
 This has been lightly tested with fstests.  Enjoy!
 
 Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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Merge tag 'fix-percpu-lists-6.6_2023-09-12' of https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux into xfs-6.6-fixesA

xfs: fix cpu hotplug mess

Ritesh and Eric separately reported crashes in XFS's hook function for
CPU hot remove if the remove event races with a filesystem being
mounted.  I also noticed via generic/650 that once in a while the log
will shut down over an apparent overrun of a transaction reservation;
this turned out to be due to CIL percpu list aggregation failing to pick
up the percpu list items from a dying CPU.

Either way, the solution here is to eliminate the need for a CPU dying
hook by using a private cpumask to track which CPUs have added to their
percpu lists directly, and iterating with that mask.  This fixes the log
problems and (I think) solves a theoretical UAF bug in the inodegc code
too.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

* tag 'fix-percpu-lists-6.6_2023-09-12' of https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux:
  xfs: remove CPU hotplug infrastructure
  xfs: remove the all-mounts list
  xfs: use per-mount cpumask to track nonempty percpu inodegc lists
  xfs: fix per-cpu CIL structure aggregation racing with dying cpus
This commit is contained in:
Chandan Babu R 2023-09-13 10:11:44 +05:30
commit 0a229c935a
7 changed files with 56 additions and 183 deletions
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