On Wed, 13 Sept 2023 at 14:13, Pavel Begunkov <asml.silence@xxxxxxxxx> wrote: > > 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@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > ================================================================== > > 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. It's a simple bit flag set & read, I'd go for READ_ONCE() (and WRITE_ONCE() - but up to you, these bitflag sets & reads have been ok with just the READ_ONCE(), and KCSAN currently doesn't care if there's a WRITE_ONCE() or not). > value changed: 0x0000000d -> 0x0000000b This is interesting though - it says that it observed 2 bits being flipped. We don't see where IO_WORKER_F_FREE was unset though.