Re: [PATCH v2] mm/memcontrol: fix stuck FLUSHING_CACHED_CHARGE bit on isolated cpus

[Shakeel Butt <shakeel.butt@linux.dev>]

On Fri, Aug 28, 2026 at 12:20:18PM -0700, Andrew Morton wrote:
> On Fri, 28 Aug 2026 13:50:36 -0400 Rik van Riel <riel@surriel.com> wrote:
> 
> > When drain_all_stock() sets FLUSHING_CACHED_CHARGE before checking
> > isolation, schedule_drain_work() can drop the work in a separate RCU
> > critical section, and housekeeping_update()'s synchronize_rcu() can race
> > that second check, leaving the flag set.
> > 
> > drain_local_stock() only clears the bit for work that ran, so the flag
> > remains set and the stock is never drained again.
> > 
> > Have schedule_drain_work() return whether the work was queued, and clear
> > FLUSHING_CACHED_CHARGE in drain_all_stock() when the remote CPU is
> > isolated, so future drains can retry.
> 
> Is there some Reported-by: or reproducer for this?
> 
> Given the complexity of the reproducers which Gemini developed for me, I'm
> suspecting "nope".
> 
> > Fixes: 6a792697a53a ("memcg: do not drain charge pcp caches on remote isolated cpus")
> > Cc: stable@vger.kernel.org
> 
> Why is a backport being proposed?  How does that benefit those we
> serve?
> 
> Sashiko suggests that we ain't done yet:
> 	https://sashiko.dev/#/patchset/20260828135036.7d44361f@fangorn

Haha we are never done. Just sent the fix for this new report:

http://lore.kernel.org/20260828192419.3057939-1-shakeel.butt@linux.dev