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BUG: KCSAN: data-race in evict / writeback_sb_inodes

write to 0xffff88821abd6808 of 8 bytes by task 3359 on cpu 1:
 writeback_sb_inodes+0x427/0xff0 fs/fs-writeback.c:1190
 wb_writeback+0x28d/0x6f0 fs/fs-writeback.c:1894
 wb_do_writeback+0x101/0x5f0 fs/fs-writeback.c:2039
 wb_workfn+0xc8/0x470 fs/fs-writeback.c:2080
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff88821abd6808 of 8 bytes by task 8717 on cpu 0:
 evict+0x42/0x470 fs/inode.c:559
 iput_final fs/inode.c:1652 [inline]
 iput+0x44a/0x550 fs/inode.c:1678
 dentry_unlink_inode+0x210/0x220 fs/dcache.c:374
 d_delete+0x78/0xa0 fs/dcache.c:2470
 vfs_rmdir+0x284/0x2a0 fs/namei.c:3726
 do_rmdir+0x16e/0x300 fs/namei.c:3773
 __do_sys_rmdir fs/namei.c:3791 [inline]
 __se_sys_rmdir fs/namei.c:3789 [inline]
 __x64_sys_rmdir+0x2c/0x30 fs/namei.c:3789
 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: 8717 Comm: syz-executor.4 Not tainted 5.9.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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