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SubjectRe: [PATCH] mm: memcontrol: fix blocking rstat function called from atomic cgroup1 thresholding code
On Mon, Jul 26, 2021 at 8:19 AM Rik van Riel <> 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

> Reviewed-by: Rik van Riel <>

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