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BUG: KCSAN: data-race in ext4_sync_file / writeback_single_inode

write to 0xffff888134254760 of 8 bytes by task 4438 on cpu 0:
 writeback_single_inode+0x148/0x3e0 fs/fs-writeback.c:1726
 sync_inode_metadata+0x57/0x80 fs/fs-writeback.c:2748
 ext4_fsync_nojournal fs/ext4/fsync.c:92 [inline]
 ext4_sync_file+0x359/0x670 fs/ext4/fsync.c:170
 vfs_fsync_range fs/sync.c:200 [inline]
 vfs_fsync fs/sync.c:214 [inline]
 do_fsync fs/sync.c:224 [inline]
 __do_sys_fdatasync fs/sync.c:237 [inline]
 __se_sys_fdatasync fs/sync.c:235 [inline]
 __x64_sys_fdatasync+0x7a/0xd0 fs/sync.c:235
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888134254760 of 8 bytes by task 4430 on cpu 1:
 ext4_fsync_nojournal fs/ext4/fsync.c:87 [inline]
 ext4_sync_file+0x294/0x670 fs/ext4/fsync.c:170
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2955 [inline]
 ext4_buffered_write_iter+0x3af/0x400 fs/ext4/file.c:277
 ext4_file_write_iter+0x2e7/0x11f0
 call_write_iter include/linux/fs.h:2163 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x7bc/0x900 fs/read_write.c:594
 ksys_write+0xd9/0x190 fs/read_write.c:647
 __do_sys_write fs/read_write.c:659 [inline]
 __se_sys_write fs/read_write.c:656 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:656
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000000000007 -> 0x0000000000000080

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 4430 Comm: syz-executor.1 Not tainted 5.15.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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