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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_recalc_inode

write to 0xffff888087099940 of 8 bytes by task 26616 on cpu 0:
 shmem_add_to_page_cache+0x4b0/0x6c0 mm/shmem.c:643
 shmem_getpage_gfp+0x43f/0x14c0 mm/shmem.c:1876
 shmem_fault+0x117/0x480 mm/shmem.c:2067
 __do_fault+0xa8/0x1e0 mm/memory.c:3276
 do_read_fault mm/memory.c:3673 [inline]
 do_fault mm/memory.c:3802 [inline]
 handle_pte_fault mm/memory.c:4033 [inline]
 __handle_mm_fault+0x2611/0x2cf0 mm/memory.c:4163
 handle_mm_fault+0x21c/0x540 mm/memory.c:4200
 faultin_page mm/gup.c:659 [inline]
 __get_user_pages+0x485/0x1140 mm/gup.c:870
 populate_vma_page_range+0xdc/0x100 mm/gup.c:1181
 __mm_populate+0x168/0x2b0 mm/gup.c:1229
 mm_populate include/linux/mm.h:2343 [inline]
 vm_mmap_pgoff+0x185/0x190 mm/util.c:511
 ksys_mmap_pgoff+0x96/0x420 mm/mmap.c:1597
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888087099940 of 8 bytes by task 26615 on cpu 1:
 shmem_recalc_inode+0x50/0x180 mm/shmem.c:306
 shmem_getpage_gfp+0x5ca/0x14c0 mm/shmem.c:1890
 shmem_fault+0x117/0x480 mm/shmem.c:2067
 __do_fault+0xa8/0x1e0 mm/memory.c:3276
 do_read_fault mm/memory.c:3673 [inline]
 do_fault mm/memory.c:3802 [inline]
 handle_pte_fault mm/memory.c:4033 [inline]
 __handle_mm_fault+0x2611/0x2cf0 mm/memory.c:4163
 handle_mm_fault+0x21c/0x540 mm/memory.c:4200
 faultin_page mm/gup.c:659 [inline]
 __get_user_pages+0x485/0x1140 mm/gup.c:870
 __get_user_pages_locked mm/gup.c:1057 [inline]
 get_user_pages_unlocked+0x24a/0x420 mm/gup.c:1765
 __gup_longterm_unlocked mm/gup.c:2423 [inline]
 internal_get_user_pages_fast mm/gup.c:2464 [inline]
 get_user_pages_fast+0x32d/0x350 mm/gup.c:2505
 iov_iter_get_pages+0x1d3/0x8cc lib/iov_iter.c:1323
 af_alg_make_sg+0x59/0x2b0 crypto/af_alg.c:399
 hash_sendmsg+0x2c0/0x5d0 crypto/algif_hash.c:94
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0x98/0xc0 net/socket.c:672
 __sys_sendto+0x1e2/0x2c0 net/socket.c:1998
 __do_sys_sendto net/socket.c:2010 [inline]
 __se_sys_sendto net/socket.c:2006 [inline]
 __x64_sys_sendto+0x7e/0xa0 net/socket.c:2006
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 26615 Comm: syz-executor.4 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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