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dkim=pass header.d=google.com header.s=20210112 header.b=KaBITggZ; spf=pass (imf04.hostedemail.com: domain of shakeelb@google.com designates 209.85.219.176 as permitted sender) smtp.mailfrom=shakeelb@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam12 X-Rspam-User: X-Stat-Signature: fr6w5k7mpbgkfqj5jctr686i97qp6n6m X-Rspamd-Queue-Id: 86D6A40011 X-HE-Tag: 1667957434-524774 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: On Tue, Nov 8, 2022 at 5:26 PM Andrew Morton wrote: > > On Wed, 9 Nov 2022 01:20:11 +0000 Shakeel Butt wrote: > > > However there is a small race window between the online CPUs traversal > > of percpu_counter_sum and the CPU offline callback. The offline callback > > has to traverse all the percpu_counters on the system to flush the CPU > > local data which can be a lot. During that time, the CPU which is going > > offline has already been published as offline to all the readers. So, as > > the offline callback is running, percpu_counter_sum can be called for > > one counter which has some state on the CPU going offline. Since > > percpu_counter_sum only traverses online CPUs, it will skip that > > specific CPU and the offline callback might not have flushed the state > > for that specific percpu_counter on that offlined CPU. > > LGTM. > > What are the user-visible effects of this bug? Should we cc:stable? If > so, can you identify a suitable Fixes:? > The patch which exposed this is still in mm-unstable (converting rss stats in mm_struct into percpu_counter) and other percpu_counter users don't really need this new interface. So, there is no need for a cc:stable. thanks, Shakeel