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BUG: KCSAN: data-race in ext4_remount / mnt_want_write

write to 0xffff888102a7b850 of 8 bytes by task 4358 on cpu 1:
 ext4_remount+0x3ca/0x1840 fs/ext4/super.c:5891
 legacy_reconfigure+0x8e/0xa0 fs/fs_context.c:615
 reconfigure_super+0x2d3/0x4f0 fs/super.c:906
 do_remount fs/namespace.c:2639 [inline]
 path_mount+0x1442/0x1ce0 fs/namespace.c:3227
 do_mount fs/namespace.c:3248 [inline]
 __do_sys_mount fs/namespace.c:3456 [inline]
 __se_sys_mount+0x23d/0x2e0 fs/namespace.c:3433
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3433
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888102a7b850 of 8 bytes by task 4357 on cpu 0:
 sb_rdonly include/linux/fs.h:2221 [inline]
 __mnt_is_readonly fs/namespace.c:269 [inline]
 mnt_is_readonly fs/namespace.c:313 [inline]
 __mnt_want_write fs/namespace.c:353 [inline]
 mnt_want_write+0x13e/0x220 fs/namespace.c:376
 do_rmdir+0xad/0x2e0 fs/namei.c:3941
 __do_sys_rmdir fs/namei.c:3976 [inline]
 __se_sys_rmdir fs/namei.c:3974 [inline]
 __x64_sys_rmdir+0x2c/0x30 fs/namei.c:3974
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 4357 Comm: syz-executor.2 Not tainted 5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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