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Miller" , Eric Dumazet , Gabriele Monaco , Greg Kroah-Hartman , Ingo Molnar , Jakub Kicinski , Jens Axboe , Johannes Weiner , Lai Jiangshan , Marco Crivellari , Michal Hocko , Muchun Song , Paolo Abeni , Peter Zijlstra , Phil Auld , "Rafael J . Wysocki" , Roman Gushchin , Shakeel Butt , Simon Horman , Tejun Heo , Thomas Gleixner , Vlastimil Babka , Waiman Long , Will Deacon , cgroups@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-block@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH 04/33] mm: vmstat: Prepare to protect against concurrent isolated cpuset change In-Reply-To: <47be2ff3-c25a-4aab-89fc-53921af8b0a9@baylibre.com> References: <20260101221359.22298-1-frederic@kernel.org> <20260101221359.22298-5-frederic@kernel.org> <47be2ff3-c25a-4aab-89fc-53921af8b0a9@baylibre.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: dlechner@baylibre.com, frederic@kernel.org, linux-kernel@vger.kernel.org, mkoutny@suse.com, akpm@linux-foundation.org, bhelgaas@google.com, catalin.marinas@arm.com, chenridong@huawei.com, dakr@kernel.org, davem@davemloft.net, edumazet@google.com, gmonaco@redhat.com, gregkh@linuxfoundation.org, mingo@redhat.com, kuba@kernel.org, axboe@kernel.dk, hannes@cmpxchg.org, jiangshanlai@gmail.com, marco.crivellari@suse.com, mhocko@suse.com, muchun.song@linux.dev, pabeni@redhat.com, peterz@infradead.org, pauld@redhat.com, rafael@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, horms@kernel.org, tj@kernel.org, tglx@linutronix.de, vbabka@suse.cz, longman@redhat.com, will@kernel.org, cgroups@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-block@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, netdev@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-Rspamd-Server: rspam09 X-Stat-Signature: ufnuhgaaoxp143hbxhohcf35kfyasesg X-Rspamd-Queue-Id: 9C9BA1A0006 X-Rspam-User: X-HE-Tag: 1771862945-680628 X-HE-Meta: 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 wBuX36Xy H/+i6SFIkvJWVEEj6I8PbcA9pHtMWfGGp19vB/7GBGaIien65JOpJSmCbgo6m5vVZ/O9B20BsAKJZ/ZKOZrT62V1OVsVAAORTWizHNkEYuE6MCEPww+neL0KJH3zlxQ7+Z81Fo//k8re7qaZh+KpwV7D/gzfEGn+GxSGrR396hyoVY8Iffxex85gwUW3zgmW1s5Hx0imTJnhiV24rAFCn04uhq3NzCN73I8xvZEdrwGrbW+FN0sd/Rit38CDvjBYTKXkKsdLO5uwanno= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 23 Feb 2026 16:01:03 +0000, David Lechner wrote: > > On 1/1/26 4:13 PM, Frederic Weisbecker wrote: > > The HK_TYPE_DOMAIN housekeeping cpumask will soon be made modifiable at > > runtime. In order to synchronize against vmstat workqueue to make sure > > that no asynchronous vmstat work is pending or executing on a newly made > > isolated CPU, target and queue a vmstat work under the same RCU read > > side critical section. > > > > Whenever housekeeping will update the HK_TYPE_DOMAIN cpumask, a vmstat > > workqueue flush will also be issued in a further change to make sure > > that no work remains pending after a CPU has been made isolated. > > > > Signed-off-by: Frederic Weisbecker > > --- > > mm/vmstat.c | 10 ++++++---- > > 1 file changed, 6 insertions(+), 4 deletions(-) > > > > diff --git a/mm/vmstat.c b/mm/vmstat.c > > index 65de88cdf40e..ed19c0d42de6 100644 > > --- a/mm/vmstat.c > > +++ b/mm/vmstat.c > > @@ -2144,11 +2144,13 @@ static void vmstat_shepherd(struct work_struct *w) > > * infrastructure ever noticing. Skip regular flushing from vmstat_shepherd > > * for all isolated CPUs to avoid interference with the isolated workload. > > */ > > - if (cpu_is_isolated(cpu)) > > - continue; > > + scoped_guard(rcu) { > > + if (cpu_is_isolated(cpu)) > > + continue; > > I think this might have introduced a bug - or at least an > unintentional change in the program flow. > > scoped_guard() is implemented using a for loop. Now this continue > statement will only exit the scoped_guard() scope rather than > continuing the outer for loop. This means that cond_resched() will > be called when it previously was not. Yup, I've been bitten by that once before. It lead to very subtle breakage that took me a while to figure out. I've now mentally banished the use of scoped_guard() inside any form of loop, but that's a pretty brittle strategy... M. -- Without deviation from the norm, progress is not possible.