From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 63DB924DD15; Wed, 24 Dec 2025 15:37:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766590655; cv=none; b=Bbu2n/LdFYX382ehr+dJMAmpd/Q40HqHHbrTyhmiuPD/BCRN27MSs9x+qB1FpbYP1keZd0y20krmiytpD1OF1Ane5o3Al59jSXjTFo1nH3RTUYzOH+fapgrTxMBUQA20HGcD4qVKJADj5KNfeYkw9i57yUj/csSus1e9sOspRGU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766590655; c=relaxed/simple; bh=Kq2IKIwGlEg3jCMrjcxejf8rYj77mjFHSMzj/fyqpVo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=V48ZIdyTDtmm1PnkdosamMuV0Hmx6YrCxolpw17DPt5/5VHt2zaQfA727rHxYz6HZJy5dyswAZynX3lfek3dGQApVRMfk5xsEiO1VpBKYETmcFhoorovBr8GhW8XzX+KBXECOL6g9INxg8b4dIsKgh4UJ0vchbpy6S32cZ04Uio= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HU3PatpK; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="HU3PatpK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B748EC4CEF7; Wed, 24 Dec 2025 15:37:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1766590654; bh=Kq2IKIwGlEg3jCMrjcxejf8rYj77mjFHSMzj/fyqpVo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; 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: Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 [...]