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b=HU3PatpKRIH9r9cf9LBg691ulT/Eg1MJt3PwpZ81oJMY10QzYmgdQmgCfr+YGB3zy y6vB3BU9UbJqOz65JZBXcJRGqkGISFl6LNo0j4mTUZRqoOZqiPNrc3S2pCa8V0qoZ1 +2jZyqLxwO2guSPLJD2sTmD3wkg4gFWLd2L0VltOb/YocfwqpATjDiuqJEC16UnFJs AigKEHXfgKcPIGA5EIKmFMkOMyzYaiQ6y21iDoQYof9nFeMtIBXwnaAGCHjwrerrtE YP8jkDUUy3nANQP6xOmNAWYh8GTAjq9RVZfaDXQGaVZ8aptQKjQnCQQXhvkAgmBqbn 02ySujIllgAcw== From: SeongJae Park To: Shakeel Butt Cc: SeongJae Park , Andrew Morton , damon@lists.linux.dev, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Subject: Re: [PATCH] memcg: damon: get memcg reference before access Date: Wed, 24 Dec 2025 07:37:30 -0800 Message-ID: <20251224153731.69411-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: D04E31A001D X-Stat-Signature: p4xmhd7b8adermuozumxx1g5xcqx4uoa X-Rspam-User: X-HE-Tag: 1766590655-155015 X-HE-Meta: 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 IR9J4j2R 0cRD4uKMFyu4cYOOhOgGWqTnfprAGFVBGvfaaqXPkYLmkET0OX8XIlu992tRi8jvtQpa22Z6INgQNC7eKzeg5i4hqM2B4iQy0XUD6scl6InUFCaii9aH3TA+rwqfftylAS7T4eeUQ+S7ReaOgMVgM1pR5Hib5tG0knozpof4jRydPXH1iq48h4fpf3kU9hOYtHTuctD8gzGhvjn4= 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 Tue, 23 Dec 2025 23:51:55 -0800 Shakeel Butt wrote: > On Tue, Dec 23, 2025 at 09:21:47PM -0800, SeongJae Park wrote: > > On Tue, 23 Dec 2025 19:45:27 -0800 Shakeel Butt wrote: [...] > > > diff --git a/mm/damon/core.c b/mm/damon/core.c > > > index 4ad5f290d382..89982e0229f0 100644 > > > --- a/mm/damon/core.c > > > +++ b/mm/damon/core.c > > > @@ -2051,13 +2051,15 @@ static unsigned long damos_get_node_memcg_used_bp( > > > > > > rcu_read_lock(); > > > memcg = mem_cgroup_from_id(goal->memcg_id); > > > - rcu_read_unlock(); > > > - if (!memcg) { > > > + if (!memcg || !mem_cgroup_tryget(memcg)) { > > > > For this part, I was thinking '!memcg' part seems not technically needed > > because mem_cgroup_tryget() does the check. But I think that's just trivial, > > so this also looks good to me. > > > > Hmm !memcg check inside mem_cgroup_tryget() is a weird one. It makes > mem_cgroup_tryget() to return true for NULL parameter. We can not use > mem_cgroup_tryget() as is alone here. Oh, you're right. I should have read it more carefully. Thank you for enlightening me :) Thanks, SJ [...]