syzbot

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BUG: KCSAN: data-race in __handle_mm_fault / expand_downwards

read to 0xffff888096a880c8 of 8 bytes by task 11838 on cpu 1:
 linear_page_index include/linux/pagemap.h:453 [inline]
 __handle_mm_fault+0x12f/0x2e00 mm/memory.c:3996
 handle_mm_fault+0x21b/0x530 mm/memory.c:4112
 faultin_page mm/gup.c:640 [inline]
 __get_user_pages+0x485/0x1130 mm/gup.c:851
 populate_vma_page_range+0xe6/0x100 mm/gup.c:1235
 __mm_populate+0x168/0x2a0 mm/gup.c:1283
 mm_populate include/linux/mm.h:2347 [inline]
 vm_mmap_pgoff+0x181/0x190 mm/util.c:511
 ksys_mmap_pgoff+0x99/0x420 mm/mmap.c:1607
 __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
 __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
 __x64_sys_mmap+0x2e/0x40 arch/x86/kernel/sys_x86_64.c:91
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff888096a880c8 of 8 bytes by task 11841 on cpu 0:
 expand_downwards+0x5d7/0x9b0 mm/mmap.c:2476
 expand_stack+0x27/0x40 mm/mmap.c:2533
 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:1203
 copy_user_generic_unrolled+0x89/0xc0 arch/x86/lib/copy_user_64.S:90
 copy_to_user include/linux/uaccess.h:152 [inline]
 do_pipe2+0x90/0x150 fs/pipe.c:950
 __do_sys_pipe fs/pipe.c:971 [inline]
 __se_sys_pipe fs/pipe.c:969 [inline]
 __x64_sys_pipe+0x2a/0x40 fs/pipe.c:969
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 11841 Comm: syz-executor.0 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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