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Date:   Wed, 14 Dec 2022 12:44:46 +0100
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Message-ID: <20221214114447.1935755-1-peternewman@google.com>
Subject: [PATCH v5 0/1] Subject: x86/resctrl: Fix task CLOSID update race
From:   Peter Newman <peternewman@google.com>
To:     reinette.chatre@intel.com, fenghua.yu@intel.com
Cc:     bp@alien8.de, derkling@google.com, eranian@google.com,
        hpa@zytor.com, james.morse@arm.com, jannh@google.com,
        kpsingh@google.com, linux-kernel@vger.kernel.org, mingo@redhat.com,
        tglx@linutronix.de, x86@kernel.org,
        Peter Newman <peternewman@google.com>
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Precedence: bulk

Hi Reinette, Fenghua,

Now that we know there is a full barrier in context switch and that
smp_mb() on every task in a group update isn't nearly as expensive as
task_call_func(), I can present you a much smaller fix.

The diffs are small enough to go down to a single patch. The changelogs
are not much simpler, but hopefully this isn't as big of a concern.

This patch is different enough that I thought it necessary to remove
James's Reviewed-By.

Updates in v5:
 - Just put an smp_mb() between CLOSID/RMID stores and task_curr() calls
 - Add a diagram detailing the race to the changelog
Updates in v4:
 - Reorder the patches so that justification for sending more IPIs can
   reference the patch fixing __rdtgroup_move_task().
 - Correct tense of wording used in changelog and comments
Updates in v3:
 - Split the handling of multi-task and single-task operations into
   separate patches, now that they're handled differently.
 - Clarify justification in the commit message, including moving some of
   it out of inline code comment.
Updates in v2:
 - Following Reinette's suggestion: use task_call_func() for single
   task, IPI broadcast for group movements.
 - Rebased to v6.1-rc4

v1: https://lore.kernel.org/lkml/20221103141641.3055981-1-peternewman@google.com/
v2: https://lore.kernel.org/lkml/20221110135346.2209839-1-peternewman@google.com/
v3: https://lore.kernel.org/lkml/20221115141953.816851-1-peternewman@google.com/
v4: https://lore.kernel.org/lkml/20221129111055.953833-1-peternewman@google.com/

Thank you for your careful reviews and feedback so far.

-Peter

Peter Newman (1):
  x86/resctrl: Fix task CLOSID/RMID update race

 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)


base-commit: 830b3c68c1fb1e9176028d02ef86f3cf76aa2476
-- 
2.39.0.rc1.256.g54fd8350bd-goog