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BUG: KCSAN: data-race in __delete_from_page_cache / shmem_getpage_gfp

write to 0xffff888090fdeaf8 of 8 bytes by task 5457 on cpu 1:
 page_cache_delete mm/filemap.c:154 [inline]
 __delete_from_page_cache+0x282/0x380 mm/filemap.c:239
 __remove_mapping+0x3e2/0x490 mm/vmscan.c:928
 shrink_page_list+0x139d/0x23c0 mm/vmscan.c:1431
 reclaim_pages+0x40e/0x540 mm/vmscan.c:2143
 madvise_cold_or_pageout_pte_range+0x140d/0x16c0 include/linux/spinlock.h:394
 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+0xc6e/0x14f0 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+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888090fdeaf8 of 8 bytes by task 5453 on cpu 0:
 shmem_recalc_inode mm/shmem.c:367 [inline]
 shmem_getpage_gfp+0xb7c/0x19c0 mm/shmem.c:1930
 shmem_fault+0x16c/0x430 mm/shmem.c:2107
 __do_fault mm/memory.c:3639 [inline]
 do_shared_fault+0xc3/0x7c0 mm/memory.c:4086
 do_fault mm/memory.c:4164 [inline]
 handle_pte_fault mm/memory.c:4400 [inline]
 __handle_mm_fault mm/memory.c:4535 [inline]
 handle_mm_fault+0x1710/0x1af0 mm/memory.c:4633
 do_user_addr_fault+0x380/0x770 arch/x86/mm/fault.c:1372
 handle_page_fault arch/x86/mm/fault.c:1429 [inline]
 exc_page_fault+0xb8/0x330 arch/x86/mm/fault.c:1482
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:538

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 5453 Comm: syz-executor.4 Not tainted 5.9.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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