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AJvYcCUm8GbxDholfIke4zUQHiq60eorTxyeF6Br6catbv764fSXDqLPDqmdD3zlWLWBPTbDA++mwRVvSQ==@kvack.org X-Gm-Message-State: AOJu0YwNWCN/fdF8xgH5M4JAczqAqPxl849WAZXaIirJbWT511Drv4Rq US8c9PfKwP/BfZEWi9ViyYtZ0t0jYDwSsH9woNtM4n+BPo6X0byvmwVB83NzETa34wUt52YIMGt rC7XMx6RJDeBHDndn6Cacpn1vw3WDY2bzW0np X-Gm-Gg: ASbGncvWM6LvtGN8tk3UPv9yqfH1Jp7CGYacyt7EX4vcLauDZWm2e3btmtpYJNaQois /zuibIra3+WAabvk4vTBjOwKQ6WaCTImyNvoNzxCCOZ4N4fKHKc/mC3p8e/davaVmzNV6AfJQ2j pg9ALRdNZ5gBqdZpE1kW8Y4z8V2XL9 X-Google-Smtp-Source: AGHT+IFud1WP91EW/+hByXq9axCts1iFc8tYz89gaIq8QLiecgIxn3kPl+sWrFJpMXdxM67U5+Tskt0BJWcApjaZZ+s= X-Received: by 2002:a17:90b:3788:b0:2ee:cb5c:6c with SMTP id 98e67ed59e1d1-2f9e0800495mr4484892a91.22.1738770437015; Wed, 05 Feb 2025 07:47:17 -0800 (PST) MIME-Version: 1.0 References: <67a34e60.050a0220.50516.0040.GAE@google.com> <13bb4bbf-92e7-4c45-a3a8-a52312015f92@lucifer.local> In-Reply-To: <13bb4bbf-92e7-4c45-a3a8-a52312015f92@lucifer.local> From: Marco Elver Date: Wed, 5 Feb 2025 16:46:40 +0100 X-Gm-Features: AWEUYZnVgJu-hBrumROm17LDjgKiR98ttkKwCU-Kk9Sxf4sLEppmU-l_b4cXqAE Message-ID: Subject: Re: [syzbot] [mm?] KCSAN: data-race in mprotect_fixup / try_to_migrate_one To: Lorenzo Stoakes Cc: Jann Horn , syzbot , Liam.Howlett@oracle.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, vbabka@suse.cz, "Paul E. McKenney" Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: bjiymg8sxoj76uqhtschxuzpoxzyukng X-Rspam-User: X-Rspamd-Queue-Id: 5122B40010 X-Rspamd-Server: rspam03 X-HE-Tag: 1738770438-986517 X-HE-Meta: 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 LdDAhCmF 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 vr/KFfHy jTMUDCh7QcU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.001277, 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, 5 Feb 2025 at 16:11, 'Lorenzo Stoakes' via syzkaller-bugs wrote: > > On Wed, Feb 05, 2025 at 04:00:06PM +0100, Jann Horn wrote: > > On Wed, Feb 5, 2025 at 12:41=E2=80=AFPM syzbot > > wrote: > > > syzbot found the following issue on: > > > > > > HEAD commit: d009de7d5428 Merge tag 'livepatching-for-6.14-rc2' of= git:.. > > > git tree: upstream > > > console output: https://syzkaller.appspot.com/x/log.txt?x=3D12b678a45= 80000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=3D9e757e376= 2bd630b > > > dashboard link: https://syzkaller.appspot.com/bug?extid=3Dc2e5712cbb1= 4c95d4847 > > > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for= Debian) 2.40 > > > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > > > Downloadable assets: > > > disk image: https://storage.googleapis.com/syzbot-assets/9235000a1b88= /disk-d009de7d.raw.xz > > > vmlinux: https://storage.googleapis.com/syzbot-assets/098ef82f8ab3/vm= linux-d009de7d.xz > > > kernel image: https://storage.googleapis.com/syzbot-assets/4f51f5eb57= 82/bzImage-d009de7d.xz > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the = commit: > > > Reported-by: syzbot+c2e5712cbb14c95d4847@syzkaller.appspotmail.com > > > > > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > > BUG: KCSAN: data-race in mprotect_fixup / try_to_migrate_one [...] > I hate that we have these landmines waiting for us. Be good to find a way > to explicitly annotate this, or at least comment somehow. > > But agreed, probably adding a READ_ONCE()/WRITE_ONCE() is appropriate at > least for the proximate thing. > > It's a wonder these things don't trigger more, except you need probably > very precise timing to do it... They do trigger, but we don't send all of them to LKML. When we first introduced KCSAN, the notion of "data race" was still poorly understood. At the time we decided to pre-review a number of them (but our time to do so has been going down :-/), or let willing maintainers deal with them directly. A number of articles followed, such as: - https://lwn.net/Articles/816850/ - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/= tools/memory-model/Documentation/access-marking.txt And I think much of the community has indeed been "Calibrating your fear of big bad optimizing compilers" [https://lwn.net/Articles/799218/]. :-) If you want to see more reports (you can try to search for ones relevant to you): https://syzkaller.appspot.com/upstream?manager=3Dci2-upstream-kcsan-gce (see "moderation")