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BUG: KCSAN: data-race in ext4_remount / file_update_time

read-write to 0xffff8881442c2850 of 8 bytes by task 18962 on cpu 0:
 ext4_remount+0x393/0x1790 fs/ext4/super.c:5803
 legacy_reconfigure+0x8e/0xa0 fs/fs_context.c:615
 reconfigure_super+0x290/0x4d0 fs/super.c:904
 do_remount fs/namespace.c:2615 [inline]
 path_mount+0x13b1/0x1c10 fs/namespace.c:3200
 do_mount fs/namespace.c:3221 [inline]
 __do_sys_mount fs/namespace.c:3429 [inline]
 __se_sys_mount+0x23d/0x2e0 fs/namespace.c:3406
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3406
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881442c2850 of 8 bytes by task 8070 on cpu 1:
 file_update_time+0x143/0x3f0 fs/inode.c:1981
 file_modified+0x62/0x80 fs/inode.c:2014
 ext4_write_checks fs/ext4/file.c:248 [inline]
 ext4_buffered_write_iter+0x1f9/0x3d0 fs/ext4/file.c:265
 ext4_file_write_iter+0x45e/0x1090 fs/ext4/file.c:503
 call_write_iter include/linux/fs.h:1901 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x6d4/0x7c0 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_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: 8070 Comm: rs:main Q:Reg Not tainted 5.11.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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