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

write to 0xffff888106dc8c20 of 8 bytes by task 28363 on cpu 1:
 __add_to_page_cache_locked+0x256/0x4b0 mm/filemap.c:914
 add_to_page_cache_lru+0xa0/0x1b0 mm/filemap.c:967
 pagecache_get_page+0x6a3/0x900 mm/filemap.c:1896
 grab_cache_page_write_begin+0x3f/0x70 mm/filemap.c:3610
 ext4_da_write_begin+0x305/0x820 fs/ext4/inode.c:2984
 generic_perform_write+0x196/0x3c0 mm/filemap.c:3656
 ext4_buffered_write_iter+0x2f2/0x3f0 fs/ext4/file.c:269
 ext4_file_write_iter+0x2e7/0x11d0 fs/ext4/file.c:519
 call_write_iter include/linux/fs.h:2114 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x69d/0x770 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 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 0xffff888106dc8c20 of 8 bytes by task 5208 on cpu 0:
 ext4_writepages+0x111/0x1d10 fs/ext4/inode.c:2668
 do_writepages+0x7b/0x150 mm/page-writeback.c:2355
 __writeback_single_inode+0x80/0x440 fs/fs-writeback.c:1613
 writeback_sb_inodes+0x563/0xd10 fs/fs-writeback.c:1878
 wb_writeback+0x28e/0x700 fs/fs-writeback.c:2051
 wb_do_writeback+0x101/0x510 fs/fs-writeback.c:2196
 wb_workfn+0xc8/0x520 fs/fs-writeback.c:2237
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2276
 worker_thread+0x636/0xae0 kernel/workqueue.c:2422
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

value changed: 0x000000000000006b -> 0x000000000000006c

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 5208 Comm: kworker/u4:10 Not tainted 5.14.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
==================================================================
EXT4-fs: 54 callbacks suppressed
EXT4-fs (sda1): Delayed block allocation failed for inode 14618 at logical offset 137 with max blocks 24 with error 28
EXT4-fs (sda1): This should not happen!! Data will be lost

EXT4-fs (sda1): Total free blocks count 0
EXT4-fs (sda1): Free/Dirty block details
EXT4-fs (sda1): free_blocks=15449
EXT4-fs (sda1): dirty_blocks=10372