Re: [PATCH v5 00/11] x86,fs/resctrl: Fix long-standing issues

[Reinette Chatre <reinette.chatre@intel.com>]

Hi Everybody,

On 6/9/26 2:02 PM, Reinette Chatre wrote:
> v4: https://lore.kernel.org/lkml/cover.1780456704.git.reinette.chatre@intel.com/
> v3: https://lore.kernel.org/lkml/cover.1779476724.git.reinette.chatre@intel.com/
> v2: https://lore.kernel.org/lkml/20260515193944.15114-1-tony.luck@intel.com/
> v1: https://lore.kernel.org/all/20260508182143.14592-1-tony.luck@intel.com/
> 
> While reviewing the AET series [1] Sashiko reported a deadlock during mount,
> and a use-after-free when an L3 domain is removed during CPU offline. More issues
> were uncovered as fixes were developed and reviewed. While the goal is to
> fix all issues the races surrounding pseudo-locked regions are not yet
> solved and have been removed from this series (last appearance was in V3 of
> this series).
> 
> Applies against tip/master to ensure it considers pending x86/cache changes
> as well as the lockdep_is_cpus_held() stubs available in smp/core.
> 
> Changes since V4:
> - Add new fix to prevent out-of-bouds read when SNC is enabled and domain
>   with busy RMID goes offline.
> - Add substitute for "is domain going offline" check to workers to avoid
>   reading any event counters on soon-to-be-offline domain since its
>   cpu_mask is empty and reading an event counter on an SNC enabled system
>   depends on knowing a CPU associated with the domain.
> 
> Changes since V3:
> - Drop majority of pseudo-locking fixes, only keep the double free/double
>   list add fix.
> - Add patch to help document safe RCU list traversal.
> - See individual patches for detailed changes.
> 
> [1] https://sashiko.dev/#/patchset/20260429184858.36423-1-tony.luck%40intel.com
> 
> Reinette Chatre (8):
>   x86,fs/resctrl: Prevent out-of-bounds access while offlining CPU when
>     SNC enabled
>   x86,fs/resctrl: Document safe RCU list traversal
>   fs/resctrl: Fix deadlock on errors during mount
>   fs/resctrl: Prevent use-after-free in rdtgroup_kn_put()
>   fs/resctrl: Fix double-add of pseudo-locked region's RMID to free list
>   fs/resctrl: Prevent deadlock and use-after-free in info file handlers
>   x86/resctrl: Ensure domain fully initialized before placed on RCU list
>   fs/resctrl: Fix UAF from worker threads when domains are removed
> 
> Tony Luck (3):
>   fs/resctrl: Move functions to avoid forward references in subsequent
>     fixes
>   fs/resctrl: Free mon_data structures on rdt_get_tree() failure
>   fs/resctrl: Fix use-after-free during unmount

Addressing Sashiko [2] review feedback here:

[PATCH v5 05/11] fs/resctrl: Fix use-after-free during unmount
  Sashiko encountered a "Tool error" during review of this patch. It was able to
  complete review of identical patch submitted as part of V4 [3].

  Even though Sashiko encountered the "Tool error" it did report a new issue. To help
  make progress with the existing fixes I would like to propose that adding new fixes
  to this series be stopped. I will start a new series of fixes to address any new
  reports.

[PATCH v5 07/11] fs/resctrl: Prevent use-after-free in rdtgroup_kn_put()
[PATCH v5 08/11] fs/resctrl: Fix double-add of pseudo-locked region's RMID to free list
 The existing pseudo-locking related issues are known and have been dropped from this series
 (last appearance was in V3) while trying to determine how to fix them.

[PATCH v5 11/11] fs/resctrl: Fix UAF from worker threads when domains are removed
 Sashiko again (previously reported in V3) reported that this would trigger a lockdep splat
 on MPAM. As described in response to previous report [4] this is a false positive since
 MPAM does not support the software controller.

 Sashiko also reports that "Does this exact ID matching and premature break miss multiple
 L3 monitor domains on Sub-NUMA Clustering (SNC) systems?"
 This is a false positive since the software controller cannot be used on SNC systems. For
 confirmation, see:
 commit ac20aa423052 ("x86/resctrl: Block use of mba_MBps mount option on Sub-NUMA Cluster (SNC) systems")

After considering the latest Sashiko feedback and deciding to stop adding new fixes
to this series, I do think this series can now be considered as "settled".
If there are no concerns with this series self then I would like to proceed for it
to be considered for inclusion.

Thank you very much.

Reinette

[2] https://sashiko.dev/#/patchset/cover.1781029125.git.reinette.chatre%40intel.com
[3] https://sashiko.dev/#/patchset/cover.1780456704.git.reinette.chatre%40intel.com?part=4
[4] https://lore.kernel.org/lkml/9ea1986a-a88f-4224-b530-252e0f5cbfd0@intel.com/