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BUG: KCSAN: data-race in wbc_detach_inode / wbc_detach_inode

read to 0xffff8881297b03ee of 2 bytes by task 11759 on cpu 0:
 wbc_detach_inode+0x77/0x550 fs/fs-writeback.c:638
 __filemap_fdatawrite_range+0x1d4/0x230 mm/filemap.c:422
 file_write_and_wait_range+0xfd/0x160 mm/filemap.c:782
 __generic_file_fsync+0x59/0x190 fs/libfs.c:1000
 ext4_sync_file+0x48e/0xb00 fs/ext4/fsync.c:120
 vfs_fsync_range+0x82/0x150 fs/sync.c:197
 generic_write_sync include/linux/fs.h:2853 [inline]
 ext4_file_write_iter+0x45b/0xa00 fs/ext4/file.c:279
 call_write_iter include/linux/fs.h:1895 [inline]
 new_sync_write+0x388/0x4a0 fs/read_write.c:483
 __vfs_write+0xb1/0xc0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x18a/0x390 fs/read_write.c:542
 ksys_write+0xd5/0x1b0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x4c/0x60 fs/read_write.c:620
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff8881297b03ee of 2 bytes by task 11763 on cpu 1:
 wbc_detach_inode+0x27c/0x550 fs/fs-writeback.c:706
 __filemap_fdatawrite_range+0x1d4/0x230 mm/filemap.c:422
 generic_fadvise+0x4a0/0x4b0 mm/fadvise.c:115
 vfs_fadvise+0x92/0xa0 mm/fadvise.c:187
 ksys_fadvise64_64+0x61/0xa0 mm/fadvise.c:201
 __do_sys_fadvise64 mm/fadvise.c:216 [inline]
 __se_sys_fadvise64 mm/fadvise.c:214 [inline]
 __x64_sys_fadvise64+0x5e/0x80 mm/fadvise.c:214
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 11763 Comm: syz-executor.5 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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