Hello, On Fri, Apr 14, 2023 at 06:30:42PM +0200, Thomas Gleixner wrote: > 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(-) This has been on my mind and regretfully it's been a busy year for me. I know the merge window is around the corner, but I rebased this series onto percpu#for-6.8 [1]. I had to massage percpu_counter slightly due to some changes but other than that it largely is intact. I need to do a little bit of a more thorough pass and re-send it out, but I think it remains correct to merge. I can then pull it, give it a few days to soak in for-next and then send it to Linus either in a follow up PR or in the 2nd week of the merge window. Thomas, how does this sound to you? [1] https://git.kernel.org/pub/scm/linux/kernel/git/dennis/percpu.git/log/?h=percpu-hotplug Thanks, Dennis
