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Wed, 19 Mar 2025 11:06:47 -0700 (PDT) Date: Wed, 19 Mar 2025 14:06:43 -0400 From: Johannes Weiner To: Yosry Ahmed Cc: Greg Thelen , Tejun Heo , Michal =?iso-8859-1?Q?Koutn=FD?= , Andrew Morton , Eric Dumazet , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Eric Dumazet Subject: Re: [PATCH] cgroup/rstat: avoid disabling irqs for O(num_cpu) Message-ID: <20250319180643.GC1876369@cmpxchg.org> References: <20250319071330.898763-1-gthelen@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Mar 19, 2025 at 05:16:02PM +0000, Yosry Ahmed wrote: > @@ -365,9 +352,8 @@ __bpf_kfunc void cgroup_rstat_flush(struct cgroup *cgrp) > void cgroup_rstat_flush_hold(struct cgroup *cgrp) > __acquires(&cgroup_rstat_lock) > { > - might_sleep(); > + cgroup_rstat_flush(cgrp); > __cgroup_rstat_lock(cgrp, -1); > - cgroup_rstat_flush_locked(cgrp); > } Might as well remove cgroup_rstat_flush_hold/release entirely? There are no external users, and the concept seems moot when the lock is dropped per default. cgroup_base_stat_cputime_show() can open-code the lock/unlock to stabilize the counts while reading. (btw, why do we not have any locking around the root stats in cgroup_base_stat_cputime_show()? There isn't anything preventing a reader from seeing all zeroes if another reader runs the memset() on cgrp->bstat, is there? Or double times...)