On Mon, 2021-07-26 at 11:00 -0400, Johannes Weiner wrote: > > __mem_cgroup_threshold() indeed holds the rcu lock. In addition, the > thresholding code is invoked during stat changes, and those contexts > have irqs disabled as well. If the lock breaking occurs inside the > flush function, it will result in a sleep from an atomic context. > > Use the irsafe flushing variant in mem_cgroup_usage() to fix this While this fix is necessary, in the long term I think we may want some sort of redesign here, to make sure the irq safe version does not spin long times trying to get the statistics off some other CPU. I have seen a number of soft (IIRC) lockups deep inside the bowels of cgroup_rstat_flush_irqsafe, with the function taking multiple seconds to complete. Reviewed-by: Rik van Riel <riel@xxxxxxxxxxx>
