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BUG: KCSAN: data-race in iput / writeback_sb_inodes

write to 0xffff8881017afcf8 of 8 bytes by task 7157 on cpu 0:
 writeback_sb_inodes+0x3cd/0xd10 fs/fs-writeback.c:1867
 wb_writeback+0x28e/0x700 fs/fs-writeback.c:2051
 wb_do_writeback+0x101/0x510 fs/fs-writeback.c:2196
 wb_workfn+0xc8/0x520 fs/fs-writeback.c:2237
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2276
 worker_thread+0x636/0xae0 kernel/workqueue.c:2422
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

read to 0xffff8881017afcf8 of 8 bytes by task 23186 on cpu 1:
 iput+0x2e/0x580 fs/inode.c:1676
 dentry_unlink_inode+0x23a/0x260 fs/dcache.c:376
 d_delete+0x78/0xe0 fs/dcache.c:2505
 vfs_rmdir+0x2a6/0x2c0 fs/namei.c:3919
 do_rmdir+0x14a/0x2e0 fs/namei.c:3968
 __do_sys_rmdir fs/namei.c:3986 [inline]
 __se_sys_rmdir fs/namei.c:3984 [inline]
 __x64_sys_rmdir+0x2c/0x30 fs/namei.c:3984
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000000020001 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 23186 Comm: syz-executor.4 Tainted: G        W         5.14.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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