Messages in this thread | | | From | Thomas Gleixner <> | Subject | [patch 0/3] lib/percpu_counter, cpu/hotplug: Cure the cpu_dying_mask woes | Date | Fri, 14 Apr 2023 18:30:42 +0200 (CEST) |
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Hi!
The cpu_dying_mask is not only undocumented but also to some extent a misnomer. It's purpose is to capture the last direction of a cpu_up() or cpu_down() operation taking eventual rollback operations into account.
cpu_dying mask is not really useful for general consumption. The cpu_dying_mask bits are sticky even after cpu_up() or cpu_down() completes.
A recent fix to plug a race in the per CPU counter code picked cpu_dying_mask to cure it. Unfortunately this does not work as the author probably expected and the behaviour of cpu_dying_mask is not easy to change without breaking the only other and initial user, the scheduler.
This series addresses this by:
1) Reworking the per CPU counter hotplug mechanism so the race is fully plugged without using cpu_dying_mask
2) Replacing the cpu_dying_mask logic with hotplug core internal state which is exposed to the scheduler with a properly documented function.
The series is also available from git:
git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git smp/dying_mask
Thanks
tglx --- include/linux/cpuhotplug.h | 2 - include/linux/cpumask.h | 21 ---------------- kernel/cpu.c | 45 +++++++++++++++++++++++++++++------ kernel/sched/core.c | 4 +-- kernel/smpboot.h | 2 + lib/percpu_counter.c | 57 +++++++++++++++++++-------------------------- 6 files changed, 67 insertions(+), 64 deletions(-)
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