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BUG: KCSAN: data-race in __anon_vma_prepare / expand_downwards

write to 0xffff8881225e0f60 of 8 bytes by task 10292 on cpu 1:
 __anon_vma_prepare+0xe0/0x2b0 mm/rmap.c:201
 anon_vma_prepare include/linux/rmap.h:153 [inline]
 expand_downwards+0x841/0x9b0 mm/mmap.c:2461
 expand_stack+0x27/0x40 mm/mmap.c:2555
 do_user_addr_fault arch/x86/mm/fault.c:1413 [inline]
 __do_page_fault+0x679/0x8d0 arch/x86/mm/fault.c:1506
 do_page_fault+0x38/0x194 arch/x86/mm/fault.c:1530
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1202

read to 0xffff8881225e0f60 of 8 bytes by task 10300 on cpu 0:
 anon_vma_prepare include/linux/rmap.h:150 [inline]
 expand_downwards+0xd9/0x9b0 mm/mmap.c:2461
 expand_stack+0x27/0x40 mm/mmap.c:2555
 do_user_addr_fault arch/x86/mm/fault.c:1413 [inline]
 __do_page_fault+0x679/0x8d0 arch/x86/mm/fault.c:1506
 do_page_fault+0x38/0x194 arch/x86/mm/fault.c:1530
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1202
 ___sys_recvmsg+0x24c/0x3e0 net/socket.c:2492
 __sys_recvmsg+0x9d/0x160 net/socket.c:2537
 __do_sys_recvmsg net/socket.c:2547 [inline]
 __se_sys_recvmsg net/socket.c:2544 [inline]
 __x64_sys_recvmsg+0x51/0x70 net/socket.c:2544
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10300 Comm: syz-executor.2 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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