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BUG: KCSAN: data-race in mnt_clone_write / propagate_one

write to 0xffff88821b262330 of 4 bytes by task 17029 on cpu 1:
 propagate_one fs/pnode.c:269 [inline]
 propagate_one+0x3b3/0x550 fs/pnode.c:225
 propagate_mnt+0x22e/0x270 fs/pnode.c:320
 attach_recursive_mnt+0x66d/0x8a0 fs/namespace.c:2071
 graft_tree+0x107/0x160 fs/namespace.c:2179
 do_add_mount.isra.0+0x102/0x190 fs/namespace.c:2725
 do_new_mount_fc fs/namespace.c:2764 [inline]
 do_new_mount fs/namespace.c:2818 [inline]
 do_mount+0x12d5/0x1590 fs/namespace.c:3141
 __do_sys_mount fs/namespace.c:3350 [inline]
 __se_sys_mount fs/namespace.c:3327 [inline]
 __x64_sys_mount+0x12b/0x1a0 fs/namespace.c:3327
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88821b262330 of 4 bytes by task 17027 on cpu 0:
 __mnt_is_readonly fs/namespace.c:248 [inline]
 mnt_clone_write+0x1f/0xd0 fs/namespace.c:377
 __mnt_want_write_file+0x71/0x80 fs/namespace.c:398
 file_update_time+0x1dd/0x2d0 fs/inode.c:1907
 ext4_page_mkwrite+0xed/0x820 fs/ext4/inode.c:5945
 do_page_mkwrite+0xfa/0x210 mm/memory.c:2529
 do_shared_fault mm/memory.c:3911 [inline]
 do_fault mm/memory.c:3979 [inline]
 handle_pte_fault mm/memory.c:4215 [inline]
 __handle_mm_fault+0x2828/0x2da0 mm/memory.c:4345
 handle_mm_fault+0x21c/0x540 mm/memory.c:4382
 do_user_addr_fault arch/x86/mm/fault.c:1464 [inline]
 do_page_fault+0x48a/0xa96 arch/x86/mm/fault.c:1535
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1203

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 17027 Comm: syz-executor.0 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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