KCSAN: data-race in shmem_add_to_page_cache / shmem_getpage_gfp

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 7575fdda Merge tag 'platform-drivers-x86-v5.9-2' of git://..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11df17ff900000
kernel config: https://syzkaller.appspot.com/x/.config?x=8a615d4b735de050
dashboard link: https://syzkaller.appspot.com/bug?extid=e32fbb814c880bd90628
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b)

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e32fbb...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_getpage_gfp

write to 0xffff888109580388 of 8 bytes by task 920 on cpu 0:
shmem_add_to_page_cache+0x5d7/0x900 mm/shmem.c:718
shmem_getpage_gfp+0x821/0x19c0 mm/shmem.c:1920
shmem_fault+0x16c/0x430 mm/shmem.c:2107
__do_fault mm/memory.c:3639 [inline]
do_read_fault+0x41f/0x760 mm/memory.c:4032
do_fault mm/memory.c:4160 [inline]
handle_pte_fault mm/memory.c:4400 [inline]
__handle_mm_fault mm/memory.c:4535 [inline]
handle_mm_fault+0x14e9/0x1af0 mm/memory.c:4633
faultin_page mm/gup.c:878 [inline]
__get_user_pages+0xa3d/0x1010 mm/gup.c:1090
populate_vma_page_range mm/gup.c:1423 [inline]
__mm_populate+0x24d/0x340 mm/gup.c:1471
mm_populate include/linux/mm.h:2566 [inline]
vm_mmap_pgoff+0x133/0x170 mm/util.c:511
ksys_mmap_pgoff+0xe1/0x380 mm/mmap.c:1596
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888109580388 of 8 bytes by task 916 on cpu 1:
shmem_recalc_inode mm/shmem.c:367 [inline]
shmem_getpage_gfp+0xb7c/0x19c0 mm/shmem.c:1930
shmem_fault+0x16c/0x430 mm/shmem.c:2107
__do_fault mm/memory.c:3639 [inline]
do_read_fault+0x41f/0x760 mm/memory.c:4032
do_fault mm/memory.c:4160 [inline]
handle_pte_fault mm/memory.c:4400 [inline]
__handle_mm_fault mm/memory.c:4535 [inline]
handle_mm_fault+0x14e9/0x1af0 mm/memory.c:4633
faultin_page mm/gup.c:878 [inline]
__get_user_pages+0xa3d/0x1010 mm/gup.c:1090
__get_user_pages_locked mm/gup.c:1276 [inline]
get_user_pages_unlocked+0x148/0x570 mm/gup.c:1996
__gup_longterm_unlocked mm/gup.c:2646 [inline]
internal_get_user_pages_fast+0xfc2/0x1240 mm/gup.c:2707
get_user_pages_fast+0x46/0x60 mm/gup.c:2803
iov_iter_get_pages+0x1a3/0x850 lib/iov_iter.c:1324
af_alg_make_sg+0x45/0x250 crypto/af_alg.c:394
hash_sendmsg+0x162/0x650 crypto/algif_hash.c:94
sock_sendmsg_nosec net/socket.c:651 [inline]
sock_sendmsg net/socket.c:671 [inline]
__sys_sendto+0x2ae/0x380 net/socket.c:1992
__do_sys_sendto net/socket.c:2004 [inline]
__se_sys_sendto net/socket.c:2000 [inline]
__x64_sys_sendto+0x74/0x90 net/socket.c:2000
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 916 Comm: syz-executor.0 Not tainted 5.9.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


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[Marco Elver]

#syz invalid

Looks benign -- let it return to moderation.