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([2620:10d:c092:600::2:7e52]) by smtp.gmail.com with ESMTPSA id r25-20020aa7d599000000b005256d80cdaesm7142811edq.65.2023.09.13.05.12.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 Sep 2023 05:12:57 -0700 (PDT) Message-ID: <4e400095-7205-883b-c8fd-4aa95a1b6423@gmail.com> Date: Wed, 13 Sep 2023 13:12:22 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [io-uring?] KCSAN: data-race in io_wq_activate_free_worker / io_wq_worker_running To: syzbot , axboe@kernel.dk, io-uring@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com References: <000000000000fc6ba706053be013@google.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: <000000000000fc6ba706053be013@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 9/13/23 12:29, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: f97e18a3f2fb Merge tag 'gpio-updates-for-v6.6' of git://gi.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=12864667a80000 > kernel config: https://syzkaller.appspot.com/x/.config?x=fe440f256d065d3b > dashboard link: https://syzkaller.appspot.com/bug?extid=a36975231499dc24df44 > 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/b1781aaff038/disk-f97e18a3.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/5b915468fd6d/vmlinux-f97e18a3.xz > kernel image: https://storage.googleapis.com/syzbot-assets/abc8ece931f3/bzImage-f97e18a3.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+a36975231499dc24df44@syzkaller.appspotmail.com > > ================================================================== > BUG: KCSAN: data-race in io_wq_activate_free_worker / io_wq_worker_running > > write to 0xffff888127f736c4 of 4 bytes by task 4731 on cpu 1: > io_wq_worker_running+0x64/0xa0 io_uring/io-wq.c:668 > schedule_timeout+0xcc/0x230 kernel/time/timer.c:2167 > io_wq_worker+0x4b2/0x840 io_uring/io-wq.c:633 > ret_from_fork+0x2e/0x40 arch/x86/kernel/process.c:145 > ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304 > > read to 0xffff888127f736c4 of 4 bytes by task 4719 on cpu 0: > io_wq_get_acct io_uring/io-wq.c:168 [inline] > io_wq_activate_free_worker+0xfa/0x280 io_uring/io-wq.c:267 > io_wq_enqueue+0x262/0x450 io_uring/io-wq.c:914 1) the worst case scenario we'll choose a wrong type of worker, which is inconsequential. 2) we're changing the IO_WORKER_F_RUNNING bit, but checking for IO_WORKER_F_BOUND. The latter one is set at the very beginning, it would require compiler to be super inventive to actually hit the problem. I don't believe it's a problem, but it'll nice to attribute it properly, READ_ONCE?, or split IO_WORKER_F_BOUND out into a separate field. > io_queue_iowq+0x1d1/0x310 io_uring/io_uring.c:514 > io_queue_sqe_fallback+0x82/0xe0 io_uring/io_uring.c:2084 > io_submit_sqe io_uring/io_uring.c:2305 [inline] > io_submit_sqes+0xbd3/0xfb0 io_uring/io_uring.c:2420 > __do_sys_io_uring_enter io_uring/io_uring.c:3628 [inline] > __se_sys_io_uring_enter+0x1f8/0x1c10 io_uring/io_uring.c:3562 > __x64_sys_io_uring_enter+0x78/0x90 io_uring/io_uring.c:3562 > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > value changed: 0x0000000d -> 0x0000000b > > Reported by Kernel Concurrency Sanitizer on: > CPU: 0 PID: 4719 Comm: syz-executor.1 Not tainted 6.5.0-syzkaller-01810-gf97e18a3f2fb #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023 > ================================================================== > > > --- > This report is generated by a bot. It may contain errors. > See https://goo.gl/tpsmEJ for more information about syzbot. > syzbot engineers can be reached at syzkaller@googlegroups.com. > > syzbot will keep track of this issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > If the bug is already fixed, let syzbot know by replying with: > #syz fix: exact-commit-title > > If you want to overwrite bug's subsystems, reply with: > #syz set subsystems: new-subsystem > (See the list of subsystem names on the web dashboard) > > If the bug is a duplicate of another bug, reply with: > #syz dup: exact-subject-of-another-report > > If you want to undo deduplication, reply with: > #syz undup -- Pavel Begunkov