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Tue, 07 Jan 2025 20:34:49 -0800 (PST) MIME-Version: 1.0 References: <20250107074724.1756696-1-yosryahmed@google.com> <20250107074724.1756696-2-yosryahmed@google.com> <20250107180345.GD37530@cmpxchg.org> In-Reply-To: From: Nhat Pham Date: Wed, 8 Jan 2025 11:34:38 +0700 X-Gm-Features: AbW1kvZadO9xN9joBYCbG2hDV0vjUGMmKTGP3MBC676S2dwZUuSYc6ZPsTNGbFo Message-ID: Subject: Re: [PATCH RESEND 2/2] mm: zswap: use SRCU to synchronize with CPU hotunplug To: Yosry Ahmed Cc: Andrew Morton , Johannes Weiner , Chengming Zhou , Vitaly Wool , Barry Song , Sam Sun , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam05 X-Stat-Signature: ejjcp8tfe5f9sao19bjnqn6ucoxz7xu6 X-Rspamd-Queue-Id: 4590E1A0017 X-Rspam-User: X-HE-Tag: 1736310890-5367 X-HE-Meta: U2FsdGVkX194clcpM3YUTJaEhfSVIlkXrj2R1n2GJplpnQaucrbAPdsxJuqMQfRoiIHARpWrwqda+ORERbh1K13EZJWd4qmLWfx6Gr3yR+SvWXrLD8AWsmLieWIDKMyciHXiHOVq+fK5kpYQ8a/TsnYHX6SdU8jhueR2a0qMrWopnXiw+4WL3nzq9zYuSYfJEJsRZwh4kDRPDwSct+Nm44FZkPu2hzCyxfy3U1pHWAdlAW+eDgWlrzpYXXN1wGnRLkk9f1t13gpp7oFUU3oKC+KVYnmJZsuXvKPff75ol1XOTI4ca1zvg9WuRL2Q2rVEEHjHja8dA9935IVTvStMj7uXOzu+vg9NB6VkJVr5EcexSBqDlQcTySaDi/Y/pFpkW2dLhr3lX/85q8s8C+hLcqM/5zly54SGrtIKE0bOZL4Ob8jDlzoFMYM8A2NbMu3HiTUh+7HOKsaQqfA2ryuS91jKaHDxTwOcMgO6OJT7HtL8ewo4XqRyco0WRWrhE0CiRsxY5Ett9iIdfc4sKZiRRHt68WyeHjIvf5yETW/PxD/7gpWeZgtDs6clKFIYIZ8r9GpiGh3uYvYoSXMlIxL41OIaAspjktBE5Eh9dT9aDYAqZn/Z7Aq+7AnunCEMsYOgm5kivJ9Q9duohOH6Yf5RTG4BCpsJbhWDnIJxfmrz3V/6nMLX8V8Cl8w5vF6s0u/dhdsELMcjpElOyrX4glDBF0QtTU6JVGhmDXd0Rlv17amoyamxx79Lm2onSrwe1660hpaa9Nwfttu/OJATHP4cw28WIpZBT+VtTJ/0Y8MDUPMAzeCvKLeUDmfH56VzZC+jyX4tMEHkZX9hFGpLNV24StpeWEDlGw9ksOqz4z0dTzBBciIfopuflyZlqHO0Kq/1rCUt61FUo0E3uJjDUZvw1wippEIkeFDlgsniFAz0bxcz/G1neckfbxWihlHJH+/TLTV0N6GVyjYLtvoYd/g L2vrFUJB 5bpOahy8xkUQQqgcfKlylkH842hKMT80+cqHIbWif8/ijAPn1Bi9H3ckOB3VCnBthjVifABSfEM/pX11DfmnlDfNC1qrKVYRdYd5rTXFPRokZTRAili4PhYfSLptMFr/V3Eore2DuImr/W6H78TSVx218gyI8kH4KM2okMWqE1Xesy+xy/EAwFn1nFBZfnahKwHtQaWWomXpQKvFVXJIOmkCAkKOnXwrSX+gmn4IRGHkeAElFDt63jkjgjBZnmlEIzp9UcWJ3X7NSuj6ZN3g7oPqyvgGgimVjxsgX6pTwZDYitPOC5wpawBCuhZVNoCZNWk7lK0udi12Lo+Ra7yhWuCDDHfz7OsR3CL6rqMQeKWl1B9qmowvIGgIoK3HY2y6A4T4sOQ/hhLe/h5k= X-Bogosity: Ham, tests=bogofilter, spamicity=0.139398, 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 Wed, Jan 8, 2025 at 11:14=E2=80=AFAM Yosry Ahmed = wrote: > > On Tue, Jan 7, 2025 at 7:56=E2=80=AFPM Nhat Pham wrot= e: > > I may have found a simpler "proper" fix than disabling migration, > please see my suggestion in: > https://lore.kernel.org/lkml/CAJD7tkYpNNsbTZZqFoRh-FkXDgxONZEUPKk1YQv7-TF= MWWQRzQ@mail.gmail.com/ Discovered that thread just now - sorry, too many emails to catch up on :) Taking a look now. > > > > > Is this a frequently occured problem in the wild? If so, we can > > disable migration to firefight, and then do the proper thing down the > > line. > > I don't believe so. Actually, I think the deadlock introduced by the > previous fix is more problematic than the UAF it fixes. > > Andrew, could you please pick up patch 1 (the revert) while we figure > out the alternative fix? It's important that it lands in v6.13 to > avoid the possibility of deadlock. Figuring out an alternative fix is > less important. Agree. Let's revert the "fix" first. CPU offlining is a much rarer event than this deadlocking scenario discovered by syzbot.