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b=p7KrGyiyFbD9sM4Rlwusp5lHcU8a08mSX+AQ093gw0/dLPiWE0vPL4ZX2HX3RRCvv 6beyLoiZw1o2Uelx6CBDIt5rgfXwnQkEh0/V/ZjsSdFVSNDOTuQ4Hs4/44vpCy4smO F3vs9lsyRx0CeZR/3tObC2FxvHNaZhdG82aANyJY= Date: Wed, 28 Oct 2026 23:54:04 -0700 From: Andrew Morton To: mt4022@columbia.edu Cc: Mani Tofigh via B4 Relay , Oleg Nesterov , Christian Brauner , linux-mm@kvack.org, linux-kernel@vger.kernel.org, tz2294@columbia.edu Subject: Re: [PATCH] exit: use READ_ONCE() to read mm->owner Message-Id: <20261028235404.2a24aa50c06556eaf77a033b@linux-foundation.org> In-Reply-To: <20261027-kcsan-exit-v1-1-7c0429a29bc0@columbia.edu> References: <20261027-kcsan-exit-v1-1-7c0429a29bc0@columbia.edu> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) X-Archived-By: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: F1793A0002 X-Stat-Signature: ysc77kdk3ku35gqf3xbrgwea5pjsoywj X-Rspamd-Server: rspam06 X-Spam-Status: No, score=-7.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793256846-711359 X-HE-Meta: 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 p2M4bVAK gNssPWXAWmxiqwYyHtIYRJDZac+av8DYF8ZQiDYR81PqJviQSvd83qqbA7jCEotVNNz4AKqRm64EnfHwz6tCnVc/Pf6JfV+ZzzE/MIOQb9cv1ZYsW/G10xaet+h5YnHYgttE1VtfbQK89+YOq01bLO9f7Gez+XHyB9TSGQ/QlG+HgrP6NYr6mczyc6xw4uZUpU/utdOE/Wg3dokILWaAMmlZKZWoMVKC0+w978DQlgUgzPU9cLC0el6AarWyfxPehK6JhMouuHuxgrQPBewRfBz4xIrHhs26tjY2Ufuytfm653z2AEUsM7V1LN7tzJo5ykNkRhcmxe/gTDywsQUPFlVunGoixkxu2nNbwMQtPSwKsuQNbbDXrH4CoKfEFgomeqDeXJPA9YVnOZx1WGBSL8PPFyN1Rdge+oEnf93UzSZdTSIbdIQ5VYpxWgUd0A8sfhcsn8dAJP2zUokU= 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 Tue, 27 Oct 2026 16:09:23 -0400 Mani Tofigh via B4 Relay wrote: > mm->owner is written with WRITE_ONCE() when ownership moves to another > task, but mm_update_next_owner() reads it with a plain load. The race > is expected, so read it with READ_ONCE() to match the writer. > > [ 14.915975] BUG: KCSAN: data-race in mm_update_next_owner / try_to_set_owner > > [ 14.916154] write (marked) to 0xff11000004471b80 of 8 bytes by task 71 on cpu 0: > [ 14.916204] try_to_set_owner+0x100/0x140 > [ 14.916302] mm_update_next_owner+0x177/0x300 > ... > > [ 14.917246] read to 0xff11000004471b80 of 8 bytes by task 75 on cpu 1: > [ 14.917293] mm_update_next_owner+0x2a/0x300 > [ 14.917396] do_exit+0x575/0x18b0 > ... > > [ 14.923906] value changed: 0xff1100002ec04180 -> 0xff1100002ed3a0c0 > > Found with KCSAN while fuzzing under a deterministic hypervisor that's > currently under development. We don't want older kernels doing this either, so I suggest Fixes: cf475ad28ac3 ("cgroups: add an owner to the mm_struct") Cc: