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BUG: KCSAN: data-race in __delete_from_page_cache / shmem_getpage_gfp

write to 0xffff8880a13ef968 of 8 bytes by task 18377 on cpu 0:
 page_cache_delete mm/filemap.c:153 [inline]
 __delete_from_page_cache+0x293/0x390 mm/filemap.c:238
 __remove_mapping+0x384/0x430 mm/vmscan.c:932
 shrink_page_list+0x1409/0x23a0 mm/vmscan.c:1437
 reclaim_pages+0x4e9/0x720 mm/vmscan.c:2148
 madvise_cold_or_pageout_pte_range+0x13de/0x1630 include/linux/spinlock.h:393
 walk_pmd_range mm/pagewalk.c:89 [inline]
 walk_pud_range mm/pagewalk.c:160 [inline]
 walk_p4d_range mm/pagewalk.c:193 [inline]
 walk_pgd_range mm/pagewalk.c:229 [inline]
 __walk_page_range+0xa66/0x15a0 mm/pagewalk.c:331
 walk_page_range+0x111/0x2e0 mm/pagewalk.c:427
 madvise_pageout_page_range mm/madvise.c:521 [inline]
 madvise_pageout mm/madvise.c:557 [inline]
 madvise_vma mm/madvise.c:946 [inline]
 do_madvise+0xc67/0x14e0 mm/madvise.c:1145
 __do_sys_madvise mm/madvise.c:1171 [inline]
 __se_sys_madvise mm/madvise.c:1169 [inline]
 __x64_sys_madvise+0x3e/0x50 mm/madvise.c:1169
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880a13ef968 of 8 bytes by task 18375 on cpu 1:
 shmem_recalc_inode mm/shmem.c:305 [inline]
 shmem_getpage_gfp+0xba2/0x1940 mm/shmem.c:1867
 shmem_fault+0x16c/0x430 mm/shmem.c:2044
 __do_fault mm/memory.c:3464 [inline]
 do_shared_fault+0xc3/0x770 mm/memory.c:3911
 do_fault mm/memory.c:3989 [inline]
 handle_pte_fault mm/memory.c:4225 [inline]
 __handle_mm_fault mm/memory.c:4357 [inline]
 handle_mm_fault+0x1572/0x1930 mm/memory.c:4394
 do_user_addr_fault+0x393/0x810 arch/x86/mm/fault.c:1295
 handle_page_fault arch/x86/mm/fault.c:1365 [inline]
 exc_page_fault+0xb8/0x330 arch/x86/mm/fault.c:1418
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:542
 copy_user_enhanced_fast_string+0xe/0x30 arch/x86/lib/copy_user_64.S:204
 copy_user_generic arch/x86/include/asm/uaccess_64.h:37 [inline]
 raw_copy_to_user arch/x86/include/asm/uaccess_64.h:74 [inline]
 copyout lib/iov_iter.c:143 [inline]
 copy_page_to_iter_iovec lib/iov_iter.c:212 [inline]
 copy_page_to_iter+0x353/0x8a0 lib/iov_iter.c:921
 generic_file_buffered_read+0x10a5/0x19e0 mm/filemap.c:2130
 generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2326
 ext4_file_read_iter+0x2d6/0x420 fs/ext4/file.c:74
 call_read_iter include/linux/fs.h:1902 [inline]
 new_sync_read fs/read_write.c:415 [inline]
 vfs_read+0x523/0x590 fs/read_write.c:481
 ksys_read+0xce/0x180 fs/read_write.c:607
 __do_sys_read fs/read_write.c:617 [inline]
 __se_sys_read fs/read_write.c:615 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:615
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 18375 Comm: syz-executor.5 Not tainted 5.8.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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