KCSAN: data-race in ext4_writepages / generic_write_end

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f8456690 Merge tag 'clk-fixes-for-linus' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1395ae13100000
kernel config: https://syzkaller.appspot.com/x/.config?x=570eb530a65cd98e
dashboard link: https://syzkaller.appspot.com/bug?extid=4e49af5cf25824bfde8d
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b)
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4e49af...@syzkaller.appspotmail.com

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

write to 0xffff88811f1913b8 of 8 bytes by task 12109 on cpu 0:
i_size_write include/linux/fs.h:897 [inline]
generic_write_end+0x99/0x220 fs/buffer.c:2187
ext4_da_write_end+0x57e/0x760 fs/ext4/inode.c:3092
generic_perform_write+0x23b/0x390 mm/filemap.c:3329
ext4_buffered_write_iter+0x2cc/0x3b0 fs/ext4/file.c:270
ext4_file_write_iter+0x76f/0x1010 include/linux/fs.h:805
call_write_iter include/linux/fs.h:1908 [inline]
new_sync_write fs/read_write.c:503 [inline]
vfs_write+0x607/0x690 fs/read_write.c:578
ksys_write+0xce/0x180 fs/read_write.c:631
__do_sys_write fs/read_write.c:643 [inline]
__se_sys_write fs/read_write.c:640 [inline]
__x64_sys_write+0x3e/0x50 fs/read_write.c:640
do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88811f1913b8 of 8 bytes by task 21 on cpu 1:
i_size_read include/linux/fs.h:875 [inline]
mpage_submit_page fs/ext4/inode.c:2076 [inline]
mpage_map_and_submit_buffers fs/ext4/inode.c:2330 [inline]
mpage_map_and_submit_extent fs/ext4/inode.c:2469 [inline]
ext4_writepages+0xe0e/0x1ef0 fs/ext4/inode.c:2782
do_writepages+0x7b/0x150 mm/page-writeback.c:2354
__writeback_single_inode+0x81/0x610 fs/fs-writeback.c:1452
writeback_sb_inodes+0x5ac/0xe40 fs/fs-writeback.c:1716
wb_writeback+0x2b8/0x730 fs/fs-writeback.c:1892
wb_do_writeback+0x108/0x610 fs/fs-writeback.c:2037
wb_workfn+0xc8/0x460 fs/fs-writeback.c:2078
process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
kthread+0x20d/0x230 kernel/kthread.c:291
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 21 Comm: kworker/u4:1 Not tainted 5.8.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.