Thread (8 messages) 8 messages, 2 authors, 2021-09-17

Re: [syzbot] BUG: soft lockup in do_wp_page (4)

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From: Dmitry Vyukov <dvyukov@google.com>
Date: 2021-03-25 19:09:35
Also in: linux-mm, lkml

On Thu, Mar 25, 2021 at 7:34 PM Dmitry Vyukov [off-list ref] wrote:
quoted
On Thu, Mar 18, 2021 at 08:34:16PM +0100, Dmitry Vyukov wrote:
quoted
On Thu, Mar 18, 2021 at 8:31 PM syzbot
[off-list ref] wrote:
quoted
Hello,

syzbot found the following issue on:

HEAD commit:    bf152b0b Merge tag 'for_linus' of git://git.kernel.org/pub..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17d5264ed00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2c9917c41f0bc04b
dashboard link: https://syzkaller.appspot.com/bug?extid=0b036374a865ba0efa8e
userspace arch: arm64

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+0b036374a865ba0efa8e@syzkaller.appspotmail.com

watchdog: BUG: soft lockup - CPU#0 stuck for 23s! [syz-executor.1:3684]
+Will, arm

If I am reading this commit correctly, this is caused by:

commit cae118b6acc309539b33339e846cbb19187c164c
Author: Will Deacon
Date:   Wed Mar 3 13:49:27 2021 +0000
    arm64: Drop support for CMDLINE_EXTEND

syzbot passes lots of critical things in CONFIG_CMDLINE:
https://github.com/google/syzkaller/blob/c3c81c94865791469d376eba84f4a2d7763d3f71/dashboard/config/linux/upstream-arm64-kasan.config#L495
but also wants the bootloader args to be appended.
What is the way to do it now?
For now, there isn't a way to do it with CONFIG_CMDLINE, so I think you can
either:

  * Revert my patch for your kernels
  * Pass the arguments via QEMU's -append option
  * Take a look at one of the series which should hopefully add this
    functionality back (but with well-defined semantics) [1] [2]
Unfortunately none of these work for syzbot (and I assume other
testing environments).

syzbot does not support custom patches by design:
http://bit.do/syzbot#no-custom-patches
As any testing system, it tests the official trees.

It's not humans who start these VMs, so it's not as easy as changing
the command line after typing...
There is no support for passing args specifically to qemu, syzkaller
support not just qemu, so these things are specifically localized in
the config. Additionally there is an issue of communicating all these
scattered details to developers in bug reports. Currently syzbot
reports the kernel config and it as well captures command line.

Could you revert the patch? Is there any point in removing the
currently supported feature before the new feature lands?
FTR another instance:
https://syzkaller.appspot.com/bug?extid=b6c93d85a3f77fca7f13
https://lore.kernel.org/lkml/000000000000d7142c05be60db47@google.com/T/#u (local)

quoted
Sorry for the nuisance; I did try to fix this [3] but it's a bit of a
mess.

Will

[1] https://lore.kernel.org/linux-arch/cover.1614705851.git.christophe.leroy@csgroup.eu/ (local)
[2] https://lore.kernel.org/linux-mips/20210308235319.2988609-2-danielwa@cisco.com/#t (local)
[3] https://lore.kernel.org/r/20210225125921.13147-1-will@kernel.org (local)
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