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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_getpage_gfp

write to 0xffff8880286a9348 of 8 bytes by task 27878 on cpu 1:
 shmem_add_to_page_cache+0x5cd/0x6e0 mm/shmem.c:718
 shmem_getpage_gfp+0x86a/0x1980 mm/shmem.c:1929
 shmem_fault+0x16c/0x450 mm/shmem.c:2116
 __do_fault mm/memory.c:3637 [inline]
 do_read_fault+0x2e1/0x530 mm/memory.c:3939
 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
 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+0x94/0x2a0 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:746 [inline]
 iov_iter_fault_in_readable+0x155/0x3a0 lib/iov_iter.c:436
 generic_perform_write+0xd2/0x3a0 mm/filemap.c:3565
 ext4_buffered_write_iter+0x2e5/0x3e0 fs/ext4/file.c:269
 ext4_file_write_iter+0x48a/0x10b0 fs/ext4/file.c:502
 call_write_iter include/linux/fs.h:1977 [inline]
 aio_write+0x2b9/0x3a0 fs/aio.c:1581
 __io_submit_one fs/aio.c:1840 [inline]
 io_submit_one+0x814/0x1280 fs/aio.c:1883
 __do_sys_io_submit fs/aio.c:1942 [inline]
 __se_sys_io_submit+0xf5/0x270 fs/aio.c:1912
 __x64_sys_io_submit+0x3f/0x50 fs/aio.c:1912
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8880286a9348 of 8 bytes by task 27889 on cpu 0:
 shmem_recalc_inode mm/shmem.c:367 [inline]
 shmem_getpage_gfp+0xba0/0x1980 mm/shmem.c:1939
 shmem_fault+0x16c/0x450 mm/shmem.c:2116
 __do_fault mm/memory.c:3637 [inline]
 do_read_fault+0x2e1/0x530 mm/memory.c:3939
 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:2582 [inline]
 vm_mmap_pgoff+0x14c/0x1d0 mm/util.c:524
 ksys_mmap_pgoff+0xe1/0x380 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: 0 PID: 27889 Comm: syz-executor.5 Not tainted 5.12.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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