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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id af79cd13be357-93f56df2ad5sm349884785a.27.2026.10.21.14.24.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Oct 2026 14:24:25 -0700 (PDT) Date: Wed, 21 Oct 2026 17:24:20 -0400 From: Gregory Price To: Shakeel Butt Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Chris Down , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Sashiko Subject: Re: [PATCH] mm/page_counter: use WRITE_ONCE() for emin/elow when parent is the root Message-ID: References: <20261021204818.3431099-1-shakeel.butt@linux.dev> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261021204818.3431099-1-shakeel.butt@linux.dev> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 48395160005 X-Stat-Signature: mzim9gk3nwsjiy74bji3np4ikffewwfj X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1792617875-659696 X-HE-Meta: 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 eoxreX6M WDLbLjvg9qlobP7B9I5L2X3x9iwzs8oVfdmm1rNBtxR5LtGXZrfmZ6uLgUvbmAL/JmrGlymN/zrFXN3Fy+I0lXZnyZ/ehpZKIcXa7GVl+ihhSk1NjvvusXulC/LODbcq5XU0HolRpVFlQm6O+Nl0jR7kF9VTLrqt+rycO1ej6H4AT6Xb5z2od3/1iTIe86mILwKvF/qvfMoHPi613OsDDir++1SB1bxt/ESFnY8FID6LkiPATxhrahPyrdaBZLBFSHrGInvlF0XTvjpQ3v34CzuIu0ABDkxj2a52kFGmFZtICavDNi2WA375D6bN7FIIi2pzMMHsFUdoOn3yWQlc3In8V9IaXzD81dLw+lVPvbOnkAazmizOlLTgjMTtlAX4K5inziDnnH9tnhnqYBbeA/6a2Vgr4Rn6e18LCG2EYADtaXRo/fhigBsDUwiSIC4ej1jQhR+3NsmvNZ94= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Wed, Oct 21, 2026 at 01:48:18PM -0700, Shakeel Butt wrote: > page_counter_calculate_protection() runs without locks. Several > reclaimers can update the same counter's emin and elow at the same > time, and readers such as mem_cgroup_below_min(), mem_cgroup_protection() > and the dmem eviction code load them with READ_ONCE(). > ... > > Use WRITE_ONCE() for these two stores as well. > > There is no functional change. Readers already accept stale values, and > compilers emit a single word-sized store either way: with GCC 14 the > x86-64 object code is the same before and after this change. > > Fixes: b3a7822e5e75 ("mm, memcg: prevent mem_cgroup_protected store tearing") > Reported-by: Sashiko > Signed-off-by: Shakeel Butt Reviewed-by: Gregory Price (Meta)