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BUG: KCSAN: data-race in wbc_detach_inode / wbc_detach_inode

write to 0xffff8880a9ecf664 of 2 bytes by task 14531 on cpu 0:
 wbc_detach_inode+0x277/0x540 fs/fs-writeback.c:705
 __filemap_fdatawrite_range+0x1c6/0x220 mm/filemap.c:422
 __filemap_fdatawrite mm/filemap.c:429 [inline]
 filemap_flush+0x2a/0x40 mm/filemap.c:456
 ext4_alloc_da_blocks+0x72/0x170 fs/ext4/inode.c:3146
 ext4_release_file+0x107/0x200 fs/ext4/file.c:142
 __fput+0x1c3/0x4f0 fs/file_table.c:280
 ____fput+0x1b/0x30 fs/file_table.c:313
 task_work_run+0xf5/0x130 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x2ae/0x2c0 arch/x86/entry/common.c:164
 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
 do_syscall_64+0x36e/0x390 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880a9ecf664 of 2 bytes by task 14537 on cpu 1:
 wbc_detach_inode+0x93/0x540 fs/fs-writeback.c:639
 __filemap_fdatawrite_range+0x1c6/0x220 mm/filemap.c:422
 __filemap_fdatawrite mm/filemap.c:429 [inline]
 filemap_flush+0x2a/0x40 mm/filemap.c:456
 ext4_alloc_da_blocks+0x72/0x170 fs/ext4/inode.c:3146
 ext4_release_file+0x107/0x200 fs/ext4/file.c:142
 __fput+0x1c3/0x4f0 fs/file_table.c:280
 ____fput+0x1b/0x30 fs/file_table.c:313
 task_work_run+0xf5/0x130 kernel/task_work.c:113
 get_signal+0x1236/0x1290 kernel/signal.c:2528
 do_signal+0x2b/0x670 arch/x86/kernel/signal.c:813
 exit_to_usermode_loop+0x24a/0x2c0 arch/x86/entry/common.c:160
 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
 do_syscall_64+0x36e/0x390 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 14537 Comm: syz-executor.2 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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