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Date:   Mon, 3 Aug 2020 06:58:21 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     butt3rflyh4ck <butterflyhuangxx@...il.com>
Cc:     syzkaller <syzkaller@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: kernel panic: panic_on_warn set

On Mon, Aug 3, 2020 at 6:55 AM Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
> On Mon, Aug 3, 2020 at 5:24 AM butt3rflyh4ck <butterflyhuangxx@...il.com> wrote:
> >
> > Hi, syzkaller always get this crashes, I think this crash is not a
> > bug, maybe some wrong configs
> > cause, can you give me some help. thanks.
> >
> > log is below:
> > ffff888063151a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >  ffff888063151a80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > ==================================================================
> > Kernel panic - not syncing: panic_on_warn set ...
> > CPU: 0 PID: 18555 Comm: syz-executor.2 Tainted: G    B             5.8.0-rc7+ #3
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> > 1.10.2-1ubuntu1 04/01/2014
> > Call Trace:
> >  __dump_stack lib/dump_stack.c:77 [inline]
> >  dump_stack+0x18f/0x20d lib/dump_stack.c:118
> >  panic+0x2e3/0x75c kernel/panic.c:231
> >  end_report+0x4d/0x53 mm/kasan/report.c:104
> >  __kasan_report mm/kasan/report.c:520 [inline]
> >  kasan_report.cold+0xd/0x37 mm/kasan/report.c:530
> >  __fb_pad_aligned_buffer include/linux/fb.h:655 [inline]
> >  bit_putcs_aligned drivers/video/fbdev/core/bitblit.c:96 [inline]
> >  bit_putcs+0xbb6/0xd20 drivers/video/fbdev/core/bitblit.c:185
> >  fbcon_putcs+0x33c/0x3f0 drivers/video/fbdev/core/fbcon.c:1362
> >  do_update_region+0x399/0x630 drivers/tty/vt/vt.c:683
> >  redraw_screen+0x64c/0x770 drivers/tty/vt/vt.c:1029
> >  vc_do_resize+0x1111/0x13f0 drivers/tty/vt/vt.c:1320
> >  vt_ioctl+0x2037/0x2670 drivers/tty/vt/vt_ioctl.c:901
> >  tty_ioctl+0x1019/0x15f0 drivers/tty/tty_io.c:2656
> >  vfs_ioctl fs/ioctl.c:48 [inline]
> >  ksys_ioctl+0x11a/0x180 fs/ioctl.c:753
> >  __do_sys_ioctl fs/ioctl.c:762 [inline]
> >  __se_sys_ioctl fs/ioctl.c:760 [inline]
> >  __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:760
> >  do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
> >  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > RIP: 0033:0x467129
> > Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 48 89 f8 48
> > 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
> > 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007fb6f7854c58 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> > RAX: ffffffffffffffda RBX: 000000000071e7c0 RCX: 0000000000467129
> > RDX: 0000000020000000 RSI: 000000000000560a RDI: 0000000000000003
> > RBP: 00000000004c0bd5 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 000000000076bf00
> > R13: 0000000000000000 R14: 000000000076bf00 R15: 00007ffd478a3fc0
> > Dumping ftrace buffer:
> >    (ftrace buffer empty)
> > Kernel Offset: disabled
> > Rebooting in 1 seconds..
>
> +syzkaller mailing list, LKML
> -syzkaller-bugs to BCC
>
> Hi butt3rflyh4ck,
>
> This is a very real kernel bug, see:
> https://groups.google.com/forum/#!searchin/syzkaller-bugs/%22bit_putcs_aligned%22%7Csort:date
> There are some reproducers available if you need them.

Or if you are asking about "Kernel panic - not syncing: panic_on_warn
set" specifically, it happens because you set panic_on_warn=1 cmdline
argument. But it only happens if there is a bug happened in the kernel
before, it just turns some non-fatal bugs into fatal. So removing
panic_on_warn=1 won't help. It's the right setting for syzkaller.

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