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Fri, 14 Mar 2025 10:17:28 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 0UTnOTgC1Gc4YgAAD6G6ig (envelope-from ); Fri, 14 Mar 2025 10:17:28 +0000 Message-ID: <0b3ab5e5-e684-44ce-b6ed-276ad37784e6@suse.cz> Date: Fri, 14 Mar 2025 11:17:28 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 06/10] memcg: do obj_cgroup_put inside drain_obj_stock Content-Language: en-US To: Shakeel Butt , Andrew Morton Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Sebastian Andrzej Siewior , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team References: <20250314061511.1308152-1-shakeel.butt@linux.dev> <20250314061511.1308152-7-shakeel.butt@linux.dev> From: Vlastimil Babka In-Reply-To: <20250314061511.1308152-7-shakeel.butt@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Score: -4.30 X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_SEVEN(0.00)[11]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[linux.dev:email,suse.cz:mid] X-Spam-Flag: NO X-Spam-Level: On 3/14/25 07:15, Shakeel Butt wrote: > Previously we could not call obj_cgroup_put() inside the local lock > because on the put on the last reference, the release function > obj_cgroup_release() may try to re-acquire the local lock. However that > chain has been broken. Now simply do obj_cgroup_put() inside > drain_obj_stock() instead of returning the old objcg. > > Signed-off-by: Shakeel Butt Hm is this really safe? I can see obj_cgroup_release() doing percpu_ref_exit() -> kfree(), do we have guaranteed that allocation won't be also in a kmemcg and recurse?