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b=0mAyBXDCnNaw5HLncu9rKGdX9UpyZ+k1g/LvILACWZs2IKSyNRxxNjw6X5jUh9cDn ZoJYwVqp74Dx8dniGuBKTe3SXugx9wK7K2Ilkq/uvFfwM/JGiiTrLdu1kU8xef+l0C ASoR6UIQen/UL8X/ITMZ12tA3xD2zYqbddoZresU= Date: Fri, 28 Aug 2026 12:55:09 -0700 From: Andrew Morton To: Shakeel Butt Cc: Rik van Riel , linux-kernel@vger.kernel.org, Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , cgroups@vger.kernel.org, linux-mm@kvack.org, kernel-team@meta.com Subject: Re: [PATCH v2] mm/memcontrol: fix stuck FLUSHING_CACHED_CHARGE bit on isolated cpus Message-Id: <20260828125509.83d2e242534c2209ca253504@linux-foundation.org> In-Reply-To: References: <20260828135036.7d44361f@fangorn> <20260828122018.1a3b3be204212837fcda8e50@linux-foundation.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: j5iheca3u66886yd7jb44kec49r3haub X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 2BFF5C0003 X-Rspam-User: X-HE-Tag: 1787946911-286437 X-HE-Meta: U2FsdGVkX1/2m0jzD1VM6wu3bpTPNhsBSjEQdLKXS49SOrcK5PkTZ6karRhtwAoTlnvTY2kHtLPa6hJ8fK35LxsmzgVjngHBIDmYi8XukPihdqLUXAQie/oQEihjuY2Lall+dGZIJk0dkdgpyhBqDJJGzmA9tC4pL9VjeZ1c05N1k/cZliNA0QOwlYBnGLDp8sVkPBjKSFnD43XFw9TQ8B8mv79Dd7k3iQYfPKOhbIVFtgfyt1Ozq8VETfohFK7+St5OdYCfFoIzEeAvonU33niLyg/f1kjYs6XtNYFZnzXstH/3QnHdSrNEV2lxf0M0WpxXFxClpVhZOI+FtBKoK/YFsQE4RHc2Msa5CGquAnOAikgYOv6fYiu/ggYGQMZggtQRAglhJTIQaRJLXN/a4qMRJiGbfkJlpxGc6ky3kXqZFrbz3dNkfTsdZsI+NQOOgQGCfC+++UKRAVtHMBeZpNmWbZ+Ba1YJedbA9o8SR7Hy/U1uY/DH2GN0MXUOCc79UI6A+0sOgRq5hrxKO28D1ctvH/MPJ2FHSVeJVsb+1myr+5ZlX7iShn9hH1afBks33/RFj+FTMLyMi1oT+v2u/02lbyjmodvVQEEYNWHRGrokksPaq7A8FKXP0t9+hMO08TYGC0uoMfFRYmopoX0t6SvYcuC+rxjkV5AQ6Xc+WetN4fzxe1cOm6rRULXnKS1OrHm0uT6Qz7e82kLk9Gh9TLLgXuOqc5KyzHMfewp3YY6P9ziUMhmLc0ZzItEQbXTJ3hYKfzQrl76X2+r4ogXm4Xj/lNEyw3iSmuj9Twh7jdC9iDRPANJBrqaKOY/SyeYjDjgEyTQR65uhgl4vBt+LNiO7QzYQ+L2b58XUexz4Ebhv0yf8Z6Iio+Bf6EAbz2Lo6LaiEn57ieXHxM1rhCVkhOUq8zCotvLsv4g2dfl9AFSm1qjJs/9nkt2CFu3T8ztnhvOefvzxIDAJ5zKK/Qe VNqV/D5v JxjjAJLt1C/i1CUfx5vFiIyHf+ET3jiyU49nHkH8RMvxkBRxDLiKQ8BiKAhKESUgSnzu3LrQhr6NrqCr3HIP30UxgGz6tv7hJbBtYr5kB5XNY4KL3Tzet65jojwwAVmu53IfnzuMWL50Xf1RiXKc9iUxC/Bzw+msq/dzQqn2B7hUp+zRlTpx9hp2k0jFTG8qFjV3hl32NH+ns33RMuVjNHdKIABmDGf0CHAmpRJTD3d2/I/noh0McO1AdpTp4KgZdo85Ogn238jGKZlDpjyzO+clIkMoKb1xbl/S1SAJnNYbCGf/9834jc133WeOKDi+rS1Shs3iuotDyavhxyLyXt/79S6yxLIp9B1++IcRxKdh6iKGaVIu3ySzWTtj76M0XvWNSL2yyBruXxRYBnqOGcekbnZBLiwWYlj4EoGYNK9f6SWfxDPJIFQThaA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 28 Aug 2026 12:26:15 -0700 Shakeel Butt wrote: > 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 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 Cool. And... guess what? https://sashiko.dev/#/patchset/20260828192419.3057939-1-shakeel.butt@linux.dev