KASAN: stack-out-of-bounds Read in finish_writeback_work

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: b41dae06 Merge tag 'xfs-5.4-merge-7' of git://git.kernel.o..
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13df36d3600000
kernel config: https://syzkaller.appspot.com/x/.config?x=dfcf592db22b9132
dashboard link: https://syzkaller.appspot.com/bug?extid=012bb5f041619f9e65b8
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org
vi...@zeniv.linux.org.uk net...@vger.kernel.org]

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+012bb5...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: stack-out-of-bounds in finish_writeback_work.isra.0+0x11b/0x120
fs/fs-writeback.c:168
Read of size 8 at addr ffff8880916379c8 by task kworker/u4:8/1170

CPU: 0 PID: 1170 Comm: kworker/u4:8 Not tainted 5.3.0+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x172/0x1f0 lib/dump_stack.c:113
print_address_description.cold+0xd4/0x306 mm/kasan/report.c:351
__kasan_report.cold+0x1b/0x36 mm/kasan/report.c:482
kasan_report+0x12/0x17 mm/kasan/common.c:618
__asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
finish_writeback_work.isra.0+0x11b/0x120 fs/fs-writeback.c:168
wb_do_writeback fs/fs-writeback.c:2030 [inline]
wb_workfn+0x34f/0x11e0 fs/fs-writeback.c:2070
process_one_work+0x9af/0x1740 kernel/workqueue.c:2269
worker_thread+0x98/0xe40 kernel/workqueue.c:2415
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

The buggy address belongs to the page:
page:ffffea0002458dc0 refcount:0 mapcount:0 mapping:0000000000000000
index:0x0
flags: 0x1fffc0000000000()
raw: 01fffc0000000000 0000000000000000 ffffffff02450101 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888091637880: 00 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1
ffff888091637900: f1 00 00 f3 f3 00 00 00 00 00 00 00 00 00 00 00
> ffff888091637980: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 f3 f3 f3
^
ffff888091637a00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f1
ffff888091637a80: f1 f1 f1 00 f2 f2 f2 00 00 00 00 00 00 00 00 00
==================================================================


---
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[Dmitry Vyukov]

#syz upstream

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