On Mon, Jul 26, 2021 at 8:19 AM Rik van Riel <riel@xxxxxx> wrote: > > 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. Can you please share a bit more detail on this lockup? I am wondering if this was due to the flush not happening more often and thus the update tree is large or if there are too many concurrent flushes happening. > > Reviewed-by: Rik van Riel <riel@xxxxxxxxxxx>
