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BUG: KCSAN: data-race in __mark_inode_dirty / writeback_sb_inodes

write to 0xffff8880a57ca280 of 8 bytes by task 261 on cpu 0:
 writeback_sb_inodes+0x4b7/0xff0 fs/fs-writeback.c:1710
 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 0xffff8880a57ca280 of 8 bytes by task 8722 on cpu 1:
 __mark_inode_dirty+0xb9/0x7f0 fs/fs-writeback.c:2274
 generic_update_time fs/inode.c:1762 [inline]
 update_time fs/inode.c:1775 [inline]
 touch_atime+0x157/0x1a0 fs/inode.c:1846
 file_accessed include/linux/fs.h:2206 [inline]
 iterate_dir+0x31b/0x370 fs/readdir.c:70
 __do_sys_getdents fs/readdir.c:283 [inline]
 __se_sys_getdents+0x7f/0x190 fs/readdir.c:268
 __x64_sys_getdents+0x3f/0x50 fs/readdir.c:268
 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: 1 PID: 8722 Comm: syz-executor.4 Not tainted 5.9.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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