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BUG: KCSAN: data-race in next_uptodate_page / shmem_write_end

write to 0xffff88810c9ead40 of 8 bytes by task 17130 on cpu 0:
 i_size_write include/linux/fs.h:872 [inline]
 shmem_write_end+0x62/0x650 mm/shmem.c:2541
 generic_perform_write+0x23e/0x3a0 mm/filemap.c:3586
 __generic_file_write_iter+0x15c/0x340 mm/filemap.c:3704
 generic_file_write_iter+0x75/0x130 mm/filemap.c:3736
 call_write_iter include/linux/fs.h:1977 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x6f9/0x7e0 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88810c9ead40 of 8 bytes by task 17134 on cpu 1:
 i_size_read include/linux/fs.h:850 [inline]
 next_uptodate_page+0x373/0x780 mm/filemap.c:3061
 next_map_page mm/filemap.c:3086 [inline]
 filemap_map_pages+0x5dc/0x770 mm/filemap.c:3142
 do_fault_around mm/memory.c:3920 [inline]
 do_read_fault+0x217/0x530 mm/memory.c:3934
 do_fault mm/memory.c:4067 [inline]
 handle_pte_fault mm/memory.c:4318 [inline]
 __handle_mm_fault mm/memory.c:4453 [inline]
 handle_mm_fault+0x1019/0x1840 mm/memory.c:4551
 faultin_page mm/gup.c:850 [inline]
 __get_user_pages+0xa47/0x1000 mm/gup.c:1069
 populate_vma_page_range mm/gup.c:1402 [inline]
 __mm_populate+0x24d/0x380 mm/gup.c:1450
 mm_populate include/linux/mm.h:2570 [inline]
 vm_mmap_pgoff+0x14c/0x1d0 mm/util.c:524
 ksys_mmap_pgoff+0x2a8/0x380 mm/mmap.c:1632
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 17134 Comm: syz-executor.1 Tainted: G        W         5.12.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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