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BUG: KCSAN: data-race in filemap_map_pages / shmem_write_end

write to 0xffff888031af8390 of 8 bytes by task 10770 on cpu 0:
 i_size_write include/linux/fs.h:871 [inline]
 shmem_write_end+0x62/0x4d0 mm/shmem.c:2544
 generic_perform_write+0x23e/0x3a0 mm/filemap.c:3340
 __generic_file_write_iter+0x15c/0x330 mm/filemap.c:3458
 generic_file_write_iter+0x75/0x130 mm/filemap.c:3490
 call_write_iter include/linux/fs.h:1903 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4b0 fs/read_write.c:866
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x42a/0x780 fs/splice.c:686
 do_splice_from fs/splice.c:764 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:933
 splice_direct_to_actor+0x345/0x650 fs/splice.c:888
 do_splice_direct+0xf5/0x170 fs/splice.c:976
 do_sendfile+0x5db/0xca0 fs/read_write.c:1257
 __do_sys_sendfile64 fs/read_write.c:1312 [inline]
 __se_sys_sendfile64 fs/read_write.c:1304 [inline]
 __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1304
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888031af8390 of 8 bytes by task 10774 on cpu 1:
 i_size_read include/linux/fs.h:849 [inline]
 filemap_map_pages+0x481/0x9a0 mm/filemap.c:2876
 do_fault_around mm/memory.c:3967 [inline]
 do_read_fault+0x233/0x760 mm/memory.c:4001
 do_fault mm/memory.c:4134 [inline]
 handle_pte_fault mm/memory.c:4374 [inline]
 __handle_mm_fault mm/memory.c:4509 [inline]
 handle_mm_fault+0xfeb/0x1770 mm/memory.c:4607
 do_user_addr_fault+0x33e/0x730 arch/x86/mm/fault.c:1372
 handle_page_fault arch/x86/mm/fault.c:1429 [inline]
 exc_page_fault+0x91/0x290 arch/x86/mm/fault.c:1485
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:583
 copy_user_enhanced_fast_string+0xe/0x40 arch/x86/lib/copy_user_64.S:205
 copy_user_generic arch/x86/include/asm/uaccess_64.h:37 [inline]
 raw_copy_from_user arch/x86/include/asm/uaccess_64.h:52 [inline]
 _copy_from_user+0x7e/0xd0 lib/usercopy.c:16
 copy_from_user include/linux/uaccess.h:192 [inline]
 __get_filter+0xc7/0x210 net/core/filter.c:1495
 sk_attach_filter+0x21/0x270 net/core/filter.c:1526
 sock_setsockopt+0x125c/0x1ef0 net/core/sock.c:1060
 __sys_setsockopt+0x326/0x450 net/socket.c:2128
 __do_sys_setsockopt net/socket.c:2143 [inline]
 __se_sys_setsockopt net/socket.c:2140 [inline]
 __x64_sys_setsockopt+0x62/0x70 net/socket.c:2140
 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: 10774 Comm: syz-executor.1 Not tainted 5.10.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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