On 14/04/23 18:30, 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. > For patches 2-3: Reviewed-by: Valentin Schneider <vschneid@xxxxxxxxxx>
