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BUG: KCSAN: data-race in _ext4_show_options / parse_options

write to 0xffff888125d04078 of 4 bytes by task 19576 on cpu 0:
 handle_mount_opt fs/ext4/super.c:1985 [inline]
 parse_options+0x66b/0x1b00 fs/ext4/super.c:2231
 ext4_remount+0x381/0x14d0 fs/ext4/super.c:5491
 legacy_reconfigure+0x8e/0xa0 fs/fs_context.c:615
 reconfigure_super+0x292/0x4d0 fs/super.c:957
 do_remount fs/namespace.c:2612 [inline]
 do_mount+0x1384/0x1c00 fs/namespace.c:3191
 __do_sys_mount fs/namespace.c:3410 [inline]
 __se_sys_mount+0xd3/0x100 fs/namespace.c:3387
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3387
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888125d04078 of 4 bytes by task 1 on cpu 1:
 _ext4_show_options+0x184/0xd80 fs/ext4/super.c:2349
 ext4_show_options+0x25/0x30 fs/ext4/super.c:2424
 show_mountinfo+0x4b4/0x4e0 fs/proc_namespace.c:187
 m_show+0x34/0x40 fs/namespace.c:1329
 seq_read+0x6f9/0x900 fs/seq_file.c:248
 vfs_read+0x16d/0x590 fs/read_write.c:479
 ksys_read+0xce/0x180 fs/read_write.c:607
 __do_sys_read fs/read_write.c:617 [inline]
 __se_sys_read fs/read_write.c:615 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:615
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1 Comm: systemd Not tainted 5.8.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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