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BUG: KCSAN: data-race in __mark_inode_dirty / writeback_sb_inodes

write to 0xffff888106ca7888 of 8 bytes by task 5243 on cpu 0:
 requeue_inode fs/fs-writeback.c:1333 [inline]
 writeback_sb_inodes+0x9d3/0xd10 fs/fs-writeback.c:1905
 __writeback_inodes_wb fs/fs-writeback.c:1947 [inline]
 wb_writeback+0x327/0x700 fs/fs-writeback.c:2053
 wb_check_old_data_flush fs/fs-writeback.c:2155 [inline]
 wb_do_writeback+0x461/0x510 fs/fs-writeback.c:2208
 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 0xffff888106ca7888 of 8 bytes by task 1659 on cpu 1:
 __mark_inode_dirty+0xda/0x680 fs/fs-writeback.c:2419
 mark_buffer_dirty+0x143/0x200 fs/buffer.c:1112
 __block_commit_write fs/buffer.c:2079 [inline]
 block_write_end+0x13d/0x260 fs/buffer.c:2158
 generic_write_end+0x5e/0x180 fs/buffer.c:2172
 ext4_da_write_end+0x59b/0x730 fs/ext4/inode.c:3110
 generic_perform_write+0x22a/0x3c0 mm/filemap.c:3667
 ext4_buffered_write_iter+0x2f2/0x3f0 fs/ext4/file.c:269
 ext4_file_write_iter+0x2e7/0x11d0 fs/ext4/file.c:519
 call_write_iter include/linux/fs.h:2114 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x69d/0x770 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 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: 0x0000000000020080 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1659 Comm: rs:main Q:Reg Tainted: G        W         5.14.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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