On Tue, Nov 8, 2022 at 5:26 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Wed, 9 Nov 2022 01:20:11 +0000 Shakeel Butt <shakeelb@xxxxxxxxxx> wrote: > > > However there is a small race window between the online CPUs traversal > > of percpu_counter_sum and the CPU offline callback. The offline callback > > has to traverse all the percpu_counters on the system to flush the CPU > > local data which can be a lot. During that time, the CPU which is going > > offline has already been published as offline to all the readers. So, as > > the offline callback is running, percpu_counter_sum can be called for > > one counter which has some state on the CPU going offline. Since > > percpu_counter_sum only traverses online CPUs, it will skip that > > specific CPU and the offline callback might not have flushed the state > > for that specific percpu_counter on that offlined CPU. > > LGTM. > > What are the user-visible effects of this bug? Should we cc:stable? If > so, can you identify a suitable Fixes:? > The patch which exposed this is still in mm-unstable (converting rss stats in mm_struct into percpu_counter) and other percpu_counter users don't really need this new interface. So, there is no need for a cc:stable. thanks, Shakeel
