==================================================================
BUG: KCSAN: data-race in __add_to_page_cache_locked / ext4_writepages

write to 0xffff88808a6cadc0 of 8 bytes by task 32750 on cpu 1:
 __add_to_page_cache_locked+0x2cc/0x6e0 mm/filemap.c:867
 add_to_page_cache_lru+0xa0/0x1a0 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+0x323/0xa30 fs/ext4/inode.c:2966
 generic_perform_write+0x197/0x380 mm/filemap.c:3299
 ext4_buffered_write_iter+0x2b1/0x390 fs/ext4/file.c:270
 ext4_file_write_iter+0x4a3/0xfd0 fs/ext4/file.c:498
 call_write_iter include/linux/fs.h:1907 [inline]
 new_sync_write fs/read_write.c:484 [inline]
 __vfs_write+0x2d8/0x340 fs/read_write.c:497
 vfs_write+0x19b/0x350 fs/read_write.c:559
 ksys_write+0xce/0x180 fs/read_write.c:612
 __do_sys_write fs/read_write.c:624 [inline]
 __se_sys_write fs/read_write.c:621 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:621
 do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88808a6cadc0 of 8 bytes by task 7 on cpu 0:
 ext4_writepages+0x132/0x1cb0 fs/ext4/inode.c:2650
 do_writepages+0x7b/0x150 mm/page-writeback.c:2354
 __writeback_single_inode+0x81/0x610 fs/fs-writeback.c:1452
 writeback_sb_inodes+0x5b8/0xe00 fs/fs-writeback.c:1716
 wb_writeback+0x2b8/0x730 fs/fs-writeback.c:1892
 wb_do_writeback+0x108/0x600 fs/fs-writeback.c:2037
 wb_workfn+0xb8/0x430 fs/fs-writeback.c:2078
 process_one_work+0x3cb/0x990 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x210/0x220 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7 Comm: kworker/u4:0 Not tainted 5.8.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
==================================================================