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BUG: KCSAN: data-race in __delete_from_page_cache / shmem_getpage_gfp

write to 0xffff8881049492e0 of 8 bytes by task 17132 on cpu 0:
 page_cache_delete mm/filemap.c:147 [inline]
 __delete_from_page_cache+0x1de/0x280 mm/filemap.c:232
 __remove_mapping+0x35b/0x470 mm/vmscan.c:1174
 shrink_page_list+0x15c2/0x2670 mm/vmscan.c:1746
 reclaim_pages+0x478/0x640 mm/vmscan.c:2482
 madvise_cold_or_pageout_pte_range+0x646/0x690 mm/madvise.c:475
 walk_pmd_range mm/pagewalk.c:128 [inline]
 walk_pud_range mm/pagewalk.c:205 [inline]
 walk_p4d_range mm/pagewalk.c:240 [inline]
 walk_pgd_range mm/pagewalk.c:277 [inline]
 __walk_page_range+0x93f/0x10e0 mm/pagewalk.c:379
 walk_page_range+0x131/0x300 mm/pagewalk.c:475
 madvise_pageout_page_range mm/madvise.c:528 [inline]
 madvise_pageout mm/madvise.c:565 [inline]
 madvise_vma mm/madvise.c:993 [inline]
 do_madvise+0xa0b/0x1140 mm/madvise.c:1202
 __do_sys_madvise mm/madvise.c:1228 [inline]
 __se_sys_madvise mm/madvise.c:1226 [inline]
 __x64_sys_madvise+0x5d/0x70 mm/madvise.c:1226
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881049492e0 of 8 bytes by task 17121 on cpu 1:
 shmem_recalc_inode mm/shmem.c:364 [inline]
 shmem_getpage_gfp+0xfd9/0x13d0 mm/shmem.c:1945
 shmem_fault+0xcf/0x470 mm/shmem.c:2113
 shm_fault+0x58/0x60 ipc/shm.c:434
 __do_fault mm/memory.c:3857 [inline]
 do_read_fault mm/memory.c:4172 [inline]
 do_fault mm/memory.c:4300 [inline]
 handle_pte_fault mm/memory.c:4558 [inline]
 __handle_mm_fault mm/memory.c:4693 [inline]
 handle_mm_fault+0xbb7/0x1580 mm/memory.c:4791
 do_user_addr_fault+0x609/0xbe0 arch/x86/mm/fault.c:1390
 handle_page_fault arch/x86/mm/fault.c:1475 [inline]
 exc_page_fault+0x91/0x220 arch/x86/mm/fault.c:1531
 asm_exc_page_fault+0x1e/0x30
 __get_user_nocheck_1+0x6/0x10
 fault_in_pages_readable include/linux/pagemap.h:778 [inline]
 iov_iter_fault_in_readable+0x148/0x290 lib/iov_iter.c:453
 generic_perform_write+0xf2/0x3e0 mm/filemap.c:3760
 ext4_buffered_write_iter+0x305/0x400 fs/ext4/file.c:269
 ext4_file_write_iter+0x2e7/0x11f0
 call_write_iter include/linux/fs.h:2163 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x7bc/0x900 fs/read_write.c:594
 ksys_write+0xd9/0x190 fs/read_write.c:647
 __do_sys_write fs/read_write.c:659 [inline]
 __se_sys_write fs/read_write.c:656 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:656
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000000000000c2 -> 0x00000000000000be

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 17121 Comm: syz-executor.4 Not tainted 5.14.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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