KCSAN: data-race in nilfs_attach_log_writer / nilfs_segctor_thread

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f01c30de Merge tag 'vfs-5.10-fixes-2' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16e41906500000
kernel config: https://syzkaller.appspot.com/x/.config?x=671e27f23e60a67b
dashboard link: https://syzkaller.appspot.com/bug?extid=c08a569228495050763c
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project.git 913f6005669cfb590c99865a90bc51ed0983d09d)
CC: [konishi...@gmail.com linux-...@vger.kernel.org linux...@vger.kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c08a56...@syzkaller.appspotmail.com

NILFS (loop2): broken superblock, retrying with spare superblock (blocksize = 1024)
NILFS (loop2): broken superblock, retrying with spare superblock (blocksize = 4096)
==================================================================
BUG: KCSAN: data-race in nilfs_attach_log_writer / nilfs_segctor_thread

write to 0xffff88803585c1e8 of 8 bytes by task 6293 on cpu 1:
nilfs_segctor_thread+0x7a/0x700 fs/nilfs2/segment.c:2546
kthread+0x1fa/0x220 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff88803585c1e8 of 8 bytes by task 6288 on cpu 0:
nilfs_segctor_start_thread fs/nilfs2/segment.c:2628 [inline]
nilfs_attach_log_writer+0x4b3/0x560 fs/nilfs2/segment.c:2790
nilfs_fill_super fs/nilfs2/super.c:1072 [inline]
nilfs_mount+0x90b/0xac0 fs/nilfs2/super.c:1316
legacy_get_tree+0x70/0xc0 fs/fs_context.c:592
vfs_get_tree+0x4a/0x190 fs/super.c:1549
do_new_mount fs/namespace.c:2875 [inline]
path_mount+0x119d/0x1c10 fs/namespace.c:3205
do_mount fs/namespace.c:3218 [inline]
__do_sys_mount fs/namespace.c:3426 [inline]
__se_sys_mount+0x23d/0x2e0 fs/namespace.c:3403
__x64_sys_mount+0x63/0x70 fs/namespace.c:3403
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 6288 Comm: syz-executor.2 Not tainted 5.10.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.