Messages in this thread | | | Date | Tue, 15 Nov 2022 15:19:51 +0100 | Subject | [PATCH v3 0/2] x86/resctrl: fix task CLOSID update race | From | Peter Newman <> |
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Hi Reinette, Fenghua,
I've reorganized the patches for clarity, following James's guidance.
The patch series addresses the IPI race we discussed in the container move RFD thread[1].
The first patch changes group-wide CLOSID/RMID updates to IPI all CPUs. Now that the synchronization cost of correctly updating a single task is more than originally thought, we believe that it's cheaper to IPI all CPUs than forming a more precise CPU mask by synchronizing with all tasks in an rdtgroup, especially when there is a large number of tasks in the group. It's possible that this update could upset users who frequently delete groups with few tasks. If anyone is aware of a use case that frequently deletes groups, we can consider mitigations.
The second one uses the new task_call_func() interface to serialize updating closid and rmid with any context switch of the task. AFAICT, the implementation of this function acts like a mutex with context switch, but I'm not certain whether it is intended to be one. If this is not how task_call_func() is meant to be used, I will instead move the code performing the update under sched/ where it can be done holding the task_rq_lock() explicitly, as Reinette has suggested before[2].
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/
Thanks! -Peter
[1] https://lore.kernel.org/all/CALPaoCg2-9ARbK+MEgdvdcjJtSy_2H6YeRkLrT97zgy8Aro3Vg@mail.gmail.com/ [2] https://lore.kernel.org/lkml/d3c06fa3-83a4-7ade-6b08-3a7259aa6c4b@intel.com/
Peter Newman (2): x86/resctrl: IPI all CPUs for group updates x86/resctrl: update task closid/rmid with task_call_func()
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 128 +++++++++++-------------- 1 file changed, 58 insertions(+), 70 deletions(-)
-- 2.38.1.493.g58b659f92b-goog
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