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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_getpage_gfp

read-write to 0xffff888128477c50 of 8 bytes by task 2088 on cpu 1:
 shmem_add_to_page_cache+0x886/0xaa0 mm/shmem.c:745
 shmem_getpage_gfp+0x802/0x16c0 mm/shmem.c:1908
 shmem_fault+0xd2/0x350 mm/shmem.c:2086
 __do_fault mm/memory.c:3915 [inline]
 do_shared_fault mm/memory.c:4295 [inline]
 do_fault+0x5df/0xb20 mm/memory.c:4373
 handle_pte_fault mm/memory.c:4627 [inline]
 __handle_mm_fault mm/memory.c:4763 [inline]
 handle_mm_fault+0x825/0xa40 mm/memory.c:4861
 do_user_addr_fault+0x4cd/0x940 arch/x86/mm/fault.c:1397
 handle_page_fault arch/x86/mm/fault.c:1484 [inline]
 exc_page_fault+0x60/0x160 arch/x86/mm/fault.c:1540
 asm_exc_page_fault+0x1e/0x30
 copy_user_enhanced_fast_string+0xa/0x40
 copy_user_generic arch/x86/include/asm/uaccess_64.h:37 [inline]
 raw_copy_to_user arch/x86/include/asm/uaccess_64.h:58 [inline]
 _copy_to_user+0x72/0x90 lib/usercopy.c:33
 copy_to_user include/linux/uaccess.h:160 [inline]
 get_random_bytes_user+0x14d/0x2a0 drivers/char/random.c:562
 __do_sys_getrandom drivers/char/random.c:1491 [inline]
 __se_sys_getrandom drivers/char/random.c:1466 [inline]
 __x64_sys_getrandom+0xd6/0x130 drivers/char/random.c:1466
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888128477c50 of 8 bytes by task 2095 on cpu 0:
 shmem_recalc_inode mm/shmem.c:362 [inline]
 shmem_getpage_gfp+0x1305/0x16c0 mm/shmem.c:1918
 shmem_fault+0xd2/0x350 mm/shmem.c:2086
 __do_fault mm/memory.c:3915 [inline]
 do_read_fault mm/memory.c:4240 [inline]
 do_fault+0x500/0xb20 mm/memory.c:4369
 handle_pte_fault mm/memory.c:4627 [inline]
 __handle_mm_fault mm/memory.c:4763 [inline]
 handle_mm_fault+0x825/0xa40 mm/memory.c:4861
 faultin_page mm/gup.c:878 [inline]
 __get_user_pages+0x306/0xb80 mm/gup.c:1099
 populate_vma_page_range mm/gup.c:1442 [inline]
 __mm_populate+0x26e/0x3a0 mm/gup.c:1555
 mm_populate include/linux/mm.h:2701 [inline]
 vm_mmap_pgoff+0x160/0x1f0 mm/util.c:524
 ksys_mmap_pgoff+0xc2/0x320 mm/mmap.c:1628
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000000000031 -> 0x0000000000000032

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 2095 Comm: syz-executor.3 Not tainted 5.18.0-rc7-syzkaller-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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