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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_recalc_inode

write to 0xffff888121a93330 of 8 bytes by task 12421 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
 do_user_addr_fault arch/x86/mm/fault.c:1442 [inline]
 do_page_fault+0x4a4/0xa52 arch/x86/mm/fault.c:1517
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1203
 copy_user_enhanced_fast_string+0xe/0x30 arch/x86/lib/copy_user_64.S:204
 copy_user_generic arch/x86/include/asm/uaccess_64.h:37 [inline]
 raw_copy_from_user arch/x86/include/asm/uaccess_64.h:71 [inline]
 copyin+0xab/0xb0 lib/iov_iter.c:152
 _copy_from_iter_full+0x14e/0x580 lib/iov_iter.c:790
 copy_from_iter_full include/linux/uio.h:156 [inline]
 skb_do_copy_data_nocache include/net/sock.h:1977 [inline]
 skb_copy_to_page_nocache include/net/sock.h:2003 [inline]
 tcp_sendmsg_locked+0xd53/0x20f0 net/ipv4/tcp.c:1335
 tcp_sendmsg+0x35/0x50 net/ipv4/tcp.c:1433
 inet_sendmsg+0x69/0x90 net/ipv4/af_inet.c:807
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0x98/0xc0 net/socket.c:672
 sock_write_iter+0x186/0x240 net/socket.c:1004
 call_write_iter include/linux/fs.h:1901 [inline]
 new_sync_write+0x303/0x400 fs/read_write.c:483
 __vfs_write+0x9e/0xb0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x189/0x380 fs/read_write.c:542
 ksys_write+0x16a/0x1a0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x49/0x60 fs/read_write.c:620
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888121a93330 of 8 bytes by task 12425 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
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 12425 Comm: syz-executor.1 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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