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BUG: KCSAN: data-race in shmem_fallocate / shmem_fault

write to 0xffff88810a727618 of 8 bytes by task 30997 on cpu 1:
 shmem_fallocate+0x2e0/0x870 mm/shmem.c:2740
 vfs_fallocate+0x479/0x6d0 fs/open.c:311
 madvise_remove+0x19c/0x200 mm/madvise.c:866
 madvise_vma mm/madvise.c:928 [inline]
 do_madvise+0x4dd/0xe20 mm/madvise.c:1133
 __do_sys_madvise mm/madvise.c:1159 [inline]
 __se_sys_madvise mm/madvise.c:1157 [inline]
 __x64_sys_madvise+0x5d/0x70 mm/madvise.c:1157
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88810a727618 of 8 bytes by task 30968 on cpu 0:
 shmem_fault+0x90/0x450 mm/shmem.c:2066
 __do_fault mm/memory.c:3637 [inline]
 do_read_fault+0x2e1/0x530 mm/memory.c:3939
 do_fault mm/memory.c:4067 [inline]
 handle_pte_fault mm/memory.c:4318 [inline]
 __handle_mm_fault mm/memory.c:4453 [inline]
 handle_mm_fault+0x1019/0x1840 mm/memory.c:4551
 faultin_page mm/gup.c:850 [inline]
 __get_user_pages+0xa47/0x1000 mm/gup.c:1069
 populate_vma_page_range mm/gup.c:1402 [inline]
 __mm_populate+0x24d/0x380 mm/gup.c:1450
 mm_populate include/linux/mm.h:2582 [inline]
 vm_mmap_pgoff+0x14c/0x1d0 mm/util.c:524
 ksys_mmap_pgoff+0xe1/0x380 mm/mmap.c:1632
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 30968 Comm: syz-executor.2 Not tainted 5.12.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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