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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_get_folio_gfp

read-write to 0xffff8881265475f0 of 8 bytes by task 4110 on cpu 0:
 shmem_add_to_page_cache+0x40a/0x510 mm/shmem.c:742
 shmem_get_folio_gfp+0x923/0x1200 mm/shmem.c:1978
 shmem_fault+0xe5/0x3d0 mm/shmem.c:2163
 __do_fault mm/memory.c:4191 [inline]
 do_read_fault mm/memory.c:4540 [inline]
 do_fault mm/memory.c:4663 [inline]
 do_pte_missing mm/memory.c:3664 [inline]
 handle_pte_fault mm/memory.c:4932 [inline]
 __handle_mm_fault mm/memory.c:5072 [inline]
 handle_mm_fault+0x1224/0x2c10 mm/memory.c:5226
 faultin_page mm/gup.c:959 [inline]
 __get_user_pages+0x65d/0xc30 mm/gup.c:1223
 populate_vma_page_range mm/gup.c:1618 [inline]
 __mm_populate+0x23b/0x360 mm/gup.c:1727
 mm_populate include/linux/mm.h:3193 [inline]
 __do_sys_remap_file_pages mm/mmap.c:3017 [inline]
 __se_sys_remap_file_pages+0x447/0x580 mm/mmap.c:2943
 __x64_sys_remap_file_pages+0x67/0x80 mm/mmap.c:2943
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff8881265475f0 of 8 bytes by task 4089 on cpu 1:
 shmem_recalc_inode mm/shmem.c:360 [inline]
 shmem_get_folio_gfp+0xe1e/0x1200 mm/shmem.c:1988
 shmem_fault+0xe5/0x3d0 mm/shmem.c:2163
 __do_fault mm/memory.c:4191 [inline]
 do_read_fault mm/memory.c:4540 [inline]
 do_fault mm/memory.c:4663 [inline]
 do_pte_missing mm/memory.c:3664 [inline]
 handle_pte_fault mm/memory.c:4932 [inline]
 __handle_mm_fault mm/memory.c:5072 [inline]
 handle_mm_fault+0x1224/0x2c10 mm/memory.c:5226
 do_user_addr_fault arch/x86/mm/fault.c:1392 [inline]
 handle_page_fault arch/x86/mm/fault.c:1486 [inline]
 exc_page_fault+0x24d/0x650 arch/x86/mm/fault.c:1542
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:570
 fault_in_readable+0xf8/0x1b0
 fault_in_iov_iter_readable+0x82/0x180 lib/iov_iter.c:216
 generic_perform_write+0x10c/0x410 mm/filemap.c:3913
 ext4_buffered_write_iter+0x1f6/0x370 fs/ext4/file.c:299
 ext4_file_write_iter+0x283/0x1230
 call_write_iter include/linux/fs.h:1871 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x4ab/0x7d0 fs/read_write.c:584
 ksys_write+0xeb/0x1a0 fs/read_write.c:637
 __do_sys_write fs/read_write.c:649 [inline]
 __se_sys_write fs/read_write.c:646 [inline]
 __x64_sys_write+0x42/0x50 fs/read_write.c:646
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x00000000000000b5 -> 0x00000000000000b6

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 4089 Comm: syz-executor.0 Not tainted 6.4.0-syzkaller-07208-gc6b0271053e7 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
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