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bh=2FQBo+G9NS5s5m9Or6v/ScN1p/wGWm+FuNiuvYY6ACA=; b=pN4tX6ZFyWEQFOPQiTwkjg7y9qa0bRlaapCNyuWUSwaWTYb6mnN5jX66hpoHhHvRHeqO/D e5YIXNbIzP/4PBhL8/oF85ZOhPimml3ONrtIqIl4/A93YRuXFNDfOF17lWNZTZ32yYcxEW dbjTNDGhROHWb+VDHwyCQ7p2RmHALCiaGrgSgseztU7tzRHNTXhe1TxgYuN8gJOm5HLvFb 6LTOKKywuApbpXeJ3CeyTwG/2Qjzxor+bKZ59rhAE02gOyWufVjuGinYKcy4X71h2SNCHv C+TH+gn3bjJJfT1ckqYb0Ro18B9zYaIbcj9CByFpM9Y+/qkXu/SJXC5YHGBQ8A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1741952134; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=2FQBo+G9NS5s5m9Or6v/ScN1p/wGWm+FuNiuvYY6ACA=; b=zXTBaDHqySfpFgV+G7VyJBWir7Y4Pm+Mk8JFgK1HGEVizypNRWcb7Pr8J8qMYe7F7G9K4D RfkBFbVr4bcrWtAA== From: Sebastian Andrzej Siewior To: Vlastimil Babka Cc: Shakeel Butt , Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Subject: Re: [RFC PATCH 06/10] memcg: do obj_cgroup_put inside drain_obj_stock Message-ID: <20250314113533.jNrVXeyr@linutronix.de> References: <20250314061511.1308152-1-shakeel.butt@linux.dev> <20250314061511.1308152-7-shakeel.butt@linux.dev> <0b3ab5e5-e684-44ce-b6ed-276ad37784e6@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <0b3ab5e5-e684-44ce-b6ed-276ad37784e6@suse.cz> X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: C49B04000E X-Stat-Signature: 8fpcrdadyo3ae51uxhx3a684t95rbbup X-HE-Tag: 1741952136-640692 X-HE-Meta: U2FsdGVkX19YkMqaSoeg123ThlOckfLZtNHdq2STMIXCC31Q/JCE8guh8nKbe6p5dCxay/ZgD8ue+yrLYrXOQjsA9tzyzjdlRMvNQdb22EZMXciqCmC1Z9ITleu5paMb9gEBV+pp874WZbI/10LEu24Mr/lBIsQfhoLCTx6pDYbFkp2h2LxaJSbDTlOet4QWlTjG1ozihxCUF7Pz+hg6O5mfcfz1AY+y+QGXhwORBDhSOe1Rxrp85noUm9Zo563iu89OB4NU7sn+fi5EJLerGuZ8ArdcyvZ4H1Bzpk7DPWeUMLvExjOpQtey3+Jw5KT89l8dkGQfFUODPP8JqCH7SOVmNAp5a/Rx5lGQnIYK7HgBikFGOp2Hue+DczgVrTTosvUjLaFQHh31Zzmurcm2LlmC0FEboRWcob0FGCaPhNvQdu6oy811v07eBcYORRuM0Mq+05W/2BGGgiFCB8p40pvFLadOtcsYzFKZohkf9VSpnw7drjo8V3h0FnpCETa7dNlNN8pGL/uM96nkSNGQVZJgIDvg9h2lTu1bvraW0EMfdHsZhWlyQ0ziHVl+W+fBuW5mzymhAoSnfJEY3Q5F+LPeAw3dcuwT0SjWXno+fyPp2HCyQtbDu+lr9N+xHBc+xzm0C9ODdFAaJn2NWjJtfPbEQ6kfEIloZkRYNQghTIwhs8AHTSawjY7721j2aMuVvRG15zobdgcT9flc9Sa59MFOTiKVC67yFKDQQThl+1qBMMrAnPgKFawsaysCs9yH981+Iu0sCwNtVc8pXbBv6AtEAdZiMLiMuQCrI8ZMwuazLhh9CVPGHR9uSon9GmrwV03N/CGyx1mFEMMY7QDzhjwWw8JyxRBO0zatsrkeIUxbCup0phBqedCwaJwVNaby33J2Ju0sWPQHrGLoqXzegg8e5pY+T8y9dmPRFo7KKqfF3EDnI8rbMZhonuovLnNeqeBXEZ7NpfUQkhGya/n gQOzcUq2 RYEhYcOM3mXxIzPDv8Y8yLzZtJ1GnRvdGI21CbEwEZd/B/+V7on1rAVrjZQ58FfWm9S1Vgr9ES1LJ9Ze2VTgCUDOj9CEoSzAq4fPdaXaH7tOsqAlWCORD83L0pg2LdV2MKWSr3lyygX4WuZDcucYG9+16DfjYNL3ETu/Y8wYV9aRIDFWV+KkUdAH7iH1LRDTV2X4yw1u9T/JpGZbJci0Uwx0LHZoN0gBko2waa6OZsbaZLmU= 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 2025-03-14 11:17:28 [+0100], Vlastimil Babka wrote: > 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? This was like this until commit 5675114623872 ("mm/memcg: protect memcg_stock with a local_lock_t") at which point the put had to happen outside. This "percpu_ref_exit() -> kfree()" was also prior this commit. Sebastian