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Wed, 19 Mar 2025 12:46:11 -0700 (PDT) Date: Wed, 19 Mar 2025 15:46:10 -0400 From: Johannes Weiner To: Yosry Ahmed Cc: Greg Thelen , Tejun Heo , Michal =?iso-8859-1?Q?Koutn=FD?= , Andrew Morton , 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: <20250319194610.GF1876369@cmpxchg.org> References: <20250319071330.898763-1-gthelen@google.com> <20250319180643.GC1876369@cmpxchg.org> <20250319191638.GD1876369@cmpxchg.org> Precedence: bulk X-Mailing-List: cgroups@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: <20250319191638.GD1876369@cmpxchg.org> On Wed, Mar 19, 2025 at 03:16:42PM -0400, Johannes Weiner wrote: > On Wed, Mar 19, 2025 at 06:35:02PM +0000, Yosry Ahmed wrote: > > On Wed, Mar 19, 2025 at 02:06:43PM -0400, Johannes Weiner wrote: > > > (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...) > > > > (I think root_cgroup_cputime() operates on a stack allocated bstat, not > > cgrp->bstat) > > That was the case until: > > commit b824766504e49f3fdcbb8c722e70996a78c3636e > Author: Chen Ridong > Date: Thu Jul 4 14:01:19 2024 +0000 Nevermind, Tejun pointed me to the follow-up fix he's got already queued up: https://web.git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git/commit/?id=c4af66a95aa3bc1d4f607ebd4eea524fb58946e3 That brings it all back on the stack.