KASAN: stack-out-of-bounds Read in __schedule (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    d08970904582 Merge tag 'for-4.20-rc5-tag' of git://git.ker..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=106a5dd5400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b9cc5a440391cbfd
dashboard link: https://syzkaller.appspot.com/bug?extid=df28818b7ebe8e7d704e
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
userspace arch: i386
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12940cfb400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16fb5e25400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+df28818b7ebe8e7d704e@xxxxxxxxxxxxxxxxxxxxxxxxx

kmem_cache               161KB        165KB
Out of memory: Kill process 7764 (syz-executor613) score 0 or sacrifice  
child
Killed process 7770 (syz-executor613) total-vm:18964kB, anon-rss:2124kB,  
file-rss:4kB, shmem-rss:0kB
oom_reaper: reaped process 7770 (syz-executor613), now anon-rss:0kB,  
file-rss:0kB, shmem-rss:0kB
==================================================================
BUG: KASAN: stack-out-of-bounds in schedule_debug kernel/sched/core.c:3284  
[inline]
BUG: KASAN: stack-out-of-bounds in __schedule+0x1c1b/0x21d0  
kernel/sched/core.c:3394
Read of size 8 at addr ffff8881ce710000 by task kworker/u4:4/2620

CPU: 1 PID: 2620 Comm: kworker/u4:4 Not tainted 4.20.0-rc5+ #266
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
Call Trace:

The buggy address belongs to the page:
page:ffffea000739c400 count:1 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 dead000000000100 dead000000000200 0000000000000000
raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881ce70ff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1
 ffff8881ce70ff80: f1 00 00 f2 f2 f2 f2 f2 f2 00 f2 f2 f2 f2 f2 f2
> ffff8881ce710000: f2 00 f2 f2 f2 f2 f2 f2 f2 00 f2 f2 f2 f2 f2 f2
                   ^
 ffff8881ce710080: f2 00 f2 f2 f2 00 00 00 00 00 00 00 00 00 00 00
 ffff8881ce710100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 2620 Comm: kworker/u4:4 Tainted: G    B             4.20.0-rc5+  
#266
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
Call Trace:
oom_reaper: reaped process 7789 (syz-executor613), now anon-rss:0kB,  
file-rss:0kB, shmem-rss:0kB
rsyslogd invoked oom-killer: gfp_mask=0x6200ca(GFP_HIGHUSER_MOVABLE),  
nodemask=(null), order=0, oom_score_adj=0
rsyslogd cpuset=/ mems_allowed=0
Kernel Offset: disabled
Rebooting in 86400 seconds..


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