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BUG: KCSAN: data-race in __add_to_page_cache_locked / ext4_writepages

write to 0xffff88800f875380 of 8 bytes by task 12085 on cpu 1:
 __add_to_page_cache_locked+0x2cc/0x6e0 mm/filemap.c:867
 add_to_page_cache_lru+0xa0/0x1b0 mm/filemap.c:918
 pagecache_get_page+0x552/0x8b0 mm/filemap.c:1653
 grab_cache_page_write_begin+0x3f/0x70 mm/filemap.c:3249
 ext4_da_write_begin+0x33c/0xa30 fs/ext4/inode.c:2966
 generic_perform_write+0x196/0x390 mm/filemap.c:3299
 ext4_buffered_write_iter+0x2cc/0x3b0 fs/ext4/file.c:270
 ext4_file_write_iter+0x76f/0x1010 include/linux/fs.h:804
 call_write_iter include/linux/fs.h:1907 [inline]
 do_iter_readv_writev+0x321/0x3c0 fs/read_write.c:694
 do_iter_write+0x10e/0x470 fs/read_write.c:999
 vfs_iter_write+0x4c/0x70 fs/read_write.c:1040
 iter_file_splice_write+0x41a/0x770 fs/splice.c:750
 do_splice_from fs/splice.c:846 [inline]
 direct_splice_actor+0x95/0x160 fs/splice.c:1016
 splice_direct_to_actor+0x365/0x660 fs/splice.c:971
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x562/0xb10 fs/read_write.c:1521
 __do_sys_sendfile64 fs/read_write.c:1582 [inline]
 __se_sys_sendfile64 fs/read_write.c:1568 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1568
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88800f875380 of 8 bytes by task 12110 on cpu 0:
 ext4_writepages+0x145/0x1ef0 fs/ext4/inode.c:2650
 do_writepages+0x7b/0x150 mm/page-writeback.c:2354
 __filemap_fdatawrite_range+0x19b/0x1d0 mm/filemap.c:421
 file_write_and_wait_range+0x9f/0x120 mm/filemap.c:760
 ext4_sync_file+0xfc/0x6e0 fs/ext4/fsync.c:151
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2882 [inline]
 ext4_buffered_write_iter+0x369/0x3b0 fs/ext4/file.c:277
 ext4_file_write_iter+0x76f/0x1010 include/linux/fs.h:804
 call_write_iter include/linux/fs.h:1907 [inline]
 do_iter_readv_writev+0x321/0x3c0 fs/read_write.c:694
 do_iter_write+0x10e/0x470 fs/read_write.c:999
 vfs_iter_write+0x4c/0x70 fs/read_write.c:1040
 iter_file_splice_write+0x41a/0x770 fs/splice.c:750
 do_splice_from fs/splice.c:846 [inline]
 direct_splice_actor+0x95/0x160 fs/splice.c:1016
 splice_direct_to_actor+0x365/0x660 fs/splice.c:971
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x562/0xb10 fs/read_write.c:1521
 __do_sys_sendfile64 fs/read_write.c:1582 [inline]
 __se_sys_sendfile64 fs/read_write.c:1568 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1568
 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: 0 PID: 12110 Comm: syz-executor.0 Not tainted 5.8.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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