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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_getpage_gfp

read-write to 0xffff88801c87b2c8 of 8 bytes by task 11230 on cpu 0:
 shmem_add_to_page_cache+0x598/0x6a0 mm/shmem.c:718
 shmem_getpage_gfp+0x85a/0x1960 mm/shmem.c:1927
 shmem_fault+0x16c/0x450 mm/shmem.c:2114
 __do_fault mm/memory.c:3625 [inline]
 do_read_fault+0x403/0x760 mm/memory.c:4019
 do_fault mm/memory.c:4147 [inline]
 handle_pte_fault mm/memory.c:4387 [inline]
 __handle_mm_fault mm/memory.c:4522 [inline]
 handle_mm_fault+0xff1/0x17b0 mm/memory.c:4620
 faultin_page mm/gup.c:851 [inline]
 __get_user_pages+0xa32/0xff0 mm/gup.c:1070
 populate_vma_page_range mm/gup.c:1403 [inline]
 __mm_populate+0x24d/0x380 mm/gup.c:1451
 mm_populate include/linux/mm.h:2591 [inline]
 vm_mmap_pgoff+0x14c/0x1d0 mm/util.c:524
 ksys_mmap_pgoff+0xe1/0x380 mm/mmap.c:1634
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88801c87b2c8 of 8 bytes by task 11233 on cpu 1:
 shmem_recalc_inode mm/shmem.c:367 [inline]
 shmem_getpage_gfp+0xb9a/0x1960 mm/shmem.c:1937
 shmem_fault+0x16c/0x450 mm/shmem.c:2114
 __do_fault mm/memory.c:3625 [inline]
 do_read_fault+0x403/0x760 mm/memory.c:4019
 do_fault mm/memory.c:4147 [inline]
 handle_pte_fault mm/memory.c:4387 [inline]
 __handle_mm_fault mm/memory.c:4522 [inline]
 handle_mm_fault+0xff1/0x17b0 mm/memory.c:4620
 do_user_addr_fault+0x433/0x830 arch/x86/mm/fault.c:1393
 handle_page_fault arch/x86/mm/fault.c:1450 [inline]
 exc_page_fault+0x94/0x2a0 arch/x86/mm/fault.c:1506
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:580
 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]
 copyin lib/iov_iter.c:159 [inline]
 copy_page_from_iter_iovec lib/iov_iter.c:303 [inline]
 copy_page_from_iter+0x33d/0x570 lib/iov_iter.c:947
 process_vm_rw_pages mm/process_vm_access.c:43 [inline]
 process_vm_rw_single_vec+0x2a3/0x460 mm/process_vm_access.c:117
 process_vm_rw_core mm/process_vm_access.c:215 [inline]
 process_vm_rw+0x3a3/0x540 mm/process_vm_access.c:283
 __do_sys_process_vm_writev mm/process_vm_access.c:303 [inline]
 __se_sys_process_vm_writev mm/process_vm_access.c:298 [inline]
 __x64_sys_process_vm_writev+0x76/0x90 mm/process_vm_access.c:298
 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: 11233 Comm: syz-executor.2 Not tainted 5.11.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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