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BUG: KCSAN: data-race in __delete_from_page_cache / ext4_writepages

write to 0xffff888129aacb68 of 8 bytes by task 20367 on cpu 1:
 page_cache_delete mm/filemap.c:153 [inline]
 __delete_from_page_cache+0x1e4/0x490 mm/filemap.c:238
 __remove_mapping+0x2ea/0x540 mm/vmscan.c:925
 remove_mapping+0x3b/0xb0 mm/vmscan.c:947
 invalidate_complete_page mm/truncate.c:215 [inline]
 invalidate_inode_page+0x1bd/0x1f0 mm/truncate.c:264
 invalidate_mapping_pages+0x2fb/0x7d0 mm/truncate.c:607
 generic_fadvise+0x2e9/0x490 mm/fadvise.c:159
 vfs_fadvise+0x8a/0x90 mm/fadvise.c:187
 ksys_fadvise64_64+0x5b/0xa0 mm/fadvise.c:201
 __do_sys_fadvise64 mm/fadvise.c:216 [inline]
 __se_sys_fadvise64 mm/fadvise.c:214 [inline]
 __x64_sys_fadvise64+0x5a/0x70 mm/fadvise.c:214
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888129aacb68 of 8 bytes by task 715 on cpu 0:
 ext4_writepages+0x181/0x1d40 fs/ext4/inode.c:2639
 do_writepages+0x6b/0x170 mm/page-writeback.c:2344
 __writeback_single_inode+0xaa/0x910 fs/fs-writeback.c:1452
 writeback_sb_inodes+0x4c8/0xa10 fs/fs-writeback.c:1716
 __writeback_inodes_wb+0xe9/0x1b0 fs/fs-writeback.c:1785
 wb_writeback+0x557/0x6a0 fs/fs-writeback.c:1894
 wb_check_background_flush fs/fs-writeback.c:1962 [inline]
 wb_do_writeback fs/fs-writeback.c:2050 [inline]
 wb_workfn+0x66b/0x970 fs/fs-writeback.c:2078
 process_one_work+0x424/0x930 kernel/workqueue.c:2264
 worker_thread+0x9a/0x7e0 kernel/workqueue.c:2410
 kthread+0x1cb/0x1f0 kernel/kthread.c:255
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 715 Comm: kworker/u4:5 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
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