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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_getpage_gfp

write to 0xffff888131eca4d0 of 8 bytes by task 14418 on cpu 1:
 shmem_add_to_page_cache+0x52d/0x650 mm/shmem.c:718
 shmem_getpage_gfp+0xbdc/0x1410 mm/shmem.c:1929
 shmem_fault+0x16d/0x500 mm/shmem.c:2116
 __do_fault mm/memory.c:3680 [inline]
 do_read_fault mm/memory.c:3984 [inline]
 do_fault mm/memory.c:4112 [inline]
 handle_pte_fault mm/memory.c:4371 [inline]
 __handle_mm_fault mm/memory.c:4506 [inline]
 handle_mm_fault+0xe8d/0x1a70 mm/memory.c:4604
 do_user_addr_fault+0x60c/0xc00 arch/x86/mm/fault.c:1390
 handle_page_fault arch/x86/mm/fault.c:1475 [inline]
 exc_page_fault+0x94/0x230 arch/x86/mm/fault.c:1531
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:577
 __get_user_nocheck_1+0x6/0x10 arch/x86/lib/getuser.S:103
 fault_in_pages_readable include/linux/pagemap.h:781 [inline]
 iov_iter_fault_in_readable+0x155/0x3a0 lib/iov_iter.c:480
 generic_perform_write+0xd2/0x3a0 mm/filemap.c:3650
 ext4_buffered_write_iter+0x2f2/0x3f0 fs/ext4/file.c:269
 ext4_file_write_iter+0x2e7/0x11d0 fs/ext4/file.c:519
 call_write_iter include/linux/fs.h:2114 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x69d/0x770 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+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888131eca4d0 of 8 bytes by task 14422 on cpu 0:
 shmem_recalc_inode mm/shmem.c:367 [inline]
 shmem_getpage_gfp+0x1017/0x1410 mm/shmem.c:1939
 shmem_fault+0x16d/0x500 mm/shmem.c:2116
 __do_fault mm/memory.c:3680 [inline]
 do_read_fault mm/memory.c:3984 [inline]
 do_fault mm/memory.c:4112 [inline]
 handle_pte_fault mm/memory.c:4371 [inline]
 __handle_mm_fault mm/memory.c:4506 [inline]
 handle_mm_fault+0xe8d/0x1a70 mm/memory.c:4604
 faultin_page mm/gup.c:908 [inline]
 __get_user_pages+0x947/0xee0 mm/gup.c:1127
 populate_vma_page_range mm/gup.c:1460 [inline]
 __mm_populate+0x24d/0x380 mm/gup.c:1508
 mm_populate include/linux/mm.h:2621 [inline]
 vm_mmap_pgoff+0x145/0x1d0 mm/util.c:524
 ksys_mmap_pgoff+0xe1/0x380 mm/mmap.c:1638
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000000000239 -> 0x000000000000023a

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 14422 Comm: syz-executor.3 Not tainted 5.13.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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