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Date: Wed, 19 Jun 2024 20:49:37 +0200 From: Marco Elver <elver@...gle.com> To: Santosh Pradhan <santosh.pradhan@...il.com> Cc: syzbot <syzbot+c147f9175ec6cc7bd73b@...kaller.appspotmail.com>, axboe@...nel.dk, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com Subject: Re: [syzbot] [block?] KCSAN: data-race in block_uevent / inc_diskseq (2) On Wed, 19 Jun 2024 at 19:00, Santosh Pradhan <santosh.pradhan@...il.com> wrote: > > Hi All, > I guess this can be fixed by READ_ONCE(disk->diskseq) while reading > and WRITE_ONCE(disk->diskseq, atomic64_inc_return(&diskseq)) in > inc_diskseq() to avoid data race. > > I can probably send a patch if my understanding is correct. What you propose fixes the underlying data race. However, I wonder if there is a race condition that needs to be taken care of: whatever sees the string "DISKSEQ=<seqnum>" can end up with either the old value or new value (in this case 45 or 48 respectively). Is whoever uses this string tolerant to the value randomly changing? > Best Regards, > Santosh > > > On Wed, Jun 19, 2024 at 5:57 PM syzbot > <syzbot+c147f9175ec6cc7bd73b@...kaller.appspotmail.com> wrote: > > > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: 3d54351c64e8 Merge tag 'lsm-pr-20240617' of git://git.kern.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=12426cfa980000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=cd45aedbb3f7637b > > dashboard link: https://syzkaller.appspot.com/bug?extid=c147f9175ec6cc7bd73b > > 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/ba0a777cccff/disk-3d54351c.raw.xz > > vmlinux: https://storage.googleapis.com/syzbot-assets/a78193318c92/vmlinux-3d54351c.xz > > kernel image: https://storage.googleapis.com/syzbot-assets/54456f3d3bfe/bzImage-3d54351c.xz > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+c147f9175ec6cc7bd73b@...kaller.appspotmail.com > > > > ================================================================== > > BUG: KCSAN: data-race in block_uevent / inc_diskseq > > > > write to 0xffff888101f05220 of 8 bytes by task 3101 on cpu 0: > > inc_diskseq+0x2c/0x40 block/genhd.c:1472 > > disk_force_media_change+0x9f/0xf0 block/disk-events.c:297 > > __loop_clr_fd+0x270/0x3f0 drivers/block/loop.c:1193 > > loop_clr_fd drivers/block/loop.c:1276 [inline] > > lo_ioctl+0xea6/0x1330 drivers/block/loop.c:1578 > > blkdev_ioctl+0x35f/0x450 block/ioctl.c:676 > > vfs_ioctl fs/ioctl.c:51 [inline] > > __do_sys_ioctl fs/ioctl.c:907 [inline] > > __se_sys_ioctl+0xd3/0x150 fs/ioctl.c:893 > > __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:893 > > x64_sys_call+0x1581/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:17 > > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > > do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83 > > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > > > read to 0xffff888101f05220 of 8 bytes by task 3091 on cpu 1: > > block_uevent+0x31/0x50 block/genhd.c:1206 > > dev_uevent+0x2f3/0x380 drivers/base/core.c:2687 > > uevent_show+0x11e/0x210 drivers/base/core.c:2745 > > dev_attr_show+0x3a/0xa0 drivers/base/core.c:2437 > > sysfs_kf_seq_show+0x17c/0x250 fs/sysfs/file.c:59 > > kernfs_seq_show+0x7c/0x90 fs/kernfs/file.c:205 > > seq_read_iter+0x2d7/0x940 fs/seq_file.c:230 > > kernfs_fop_read_iter+0xc6/0x310 fs/kernfs/file.c:279 > > new_sync_read fs/read_write.c:395 [inline] > > vfs_read+0x5e6/0x6e0 fs/read_write.c:476 > > ksys_read+0xeb/0x1b0 fs/read_write.c:619 > > __do_sys_read fs/read_write.c:629 [inline] > > __se_sys_read fs/read_write.c:627 [inline] > > __x64_sys_read+0x42/0x50 fs/read_write.c:627 > > x64_sys_call+0x27e5/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:1 > > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > > do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83 > > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > > > value changed: 0x0000000000000045 -> 0x0000000000000048 > > > > Reported by Kernel Concurrency Sanitizer on: > > CPU: 1 PID: 3091 Comm: udevd Not tainted 6.10.0-rc4-syzkaller-00035-g3d54351c64e8 #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024 > > ================================================================== > > > > > > --- > > 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@...glegroups.com. > > > > syzbot will keep track of this issue. See: > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > > > If the report is already addressed, let syzbot know by replying with: > > #syz fix: exact-commit-title > > > > If you want to overwrite report's subsystems, reply with: > > #syz set subsystems: new-subsystem > > (See the list of subsystem names on the web dashboard) > > > > If the report is a duplicate of another one, reply with: > > #syz dup: exact-subject-of-another-report > > > > If you want to undo deduplication, reply with: > > #syz undup > > > > -- > You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group. > To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@...glegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/CAOuNp5n7qaZnZ_5%2BkjfA6MD3QO%3DXDhE01G1ofN3rp72um-D2%2Bw%40mail.gmail.com.
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