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BUG: KCSAN: data-race in __add_to_page_cache_locked / ext4_writepages

write to 0xffff888106b87c20 of 8 bytes by task 21335 on cpu 0:
 __add_to_page_cache_locked+0x256/0x4b0 mm/filemap.c:914
 add_to_page_cache_lru+0xa0/0x1b0 mm/filemap.c:967
 page_cache_ra_unbounded+0x262/0x410 mm/readahead.c:221
 ondemand_readahead+0x579/0x7b0 mm/readahead.c:267
 page_cache_async_ra+0x165/0x190 mm/readahead.c:607
 page_cache_async_readahead include/linux/pagemap.h:907 [inline]
 do_async_mmap_readahead+0x214/0x250 mm/filemap.c:2930
 filemap_fault+0x10a/0x7b0 mm/filemap.c:2984
 ext4_filemap_fault+0x4b/0x60 fs/ext4/inode.c:6194
 __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+0xe6d/0x1a50 mm/memory.c:4791
 faultin_page mm/gup.c:951 [inline]
 __get_user_pages+0x32b/0xbc0 mm/gup.c:1173
 populate_vma_page_range mm/gup.c:1506 [inline]
 __mm_populate+0x24d/0x380 mm/gup.c:1612
 mm_populate include/linux/mm.h:2623 [inline]
 vm_mmap_pgoff+0x142/0x1d0 mm/util.c:524
 ksys_mmap_pgoff+0x2a8/0x380 mm/mmap.c:1635
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888106b87c20 of 8 bytes by task 21342 on cpu 1:
 ext4_writepages+0x111/0x1d10 fs/ext4/inode.c:2668
 do_writepages+0x7b/0x150 mm/page-writeback.c:2355
 __filemap_fdatawrite_range+0x135/0x160 mm/filemap.c:413
 generic_fadvise+0x484/0x5d0 mm/fadvise.c:113
 vfs_fadvise mm/fadvise.c:186 [inline]
 ksys_fadvise64_64 mm/fadvise.c:200 [inline]
 __do_sys_fadvise64 mm/fadvise.c:215 [inline]
 __se_sys_fadvise64 mm/fadvise.c:213 [inline]
 __x64_sys_fadvise64+0xc5/0x100 mm/fadvise.c:213
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000000000002c9 -> 0x00000000000002ce

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 21342 Comm: syz-executor.2 Not tainted 5.14.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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