linux-kernel - Re: BUG: soft lockup in __kmalloc

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Date:   Mon, 11 Oct 2021 12:03:52 +0200
From:   Marco Elver <elver@...gle.com>
To:     Andrea Righi <andrea.righi@...onical.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: BUG: soft lockup in __kmalloc_node() with KFENCE enabled

On Mon, 11 Oct 2021 at 11:53, Andrea Righi <andrea.righi@...onical.com> wrote:
> On Mon, Oct 11, 2021 at 11:23:32AM +0200, Andrea Righi wrote:
> ...
> > > You seem to use the default 20s stall timeout. FWIW syzbot uses 160
> > > secs timeout for TCG emulation to avoid false positive warnings:
> > > https://github.com/google/syzkaller/blob/838e7e2cd9228583ca33c49a39aea4d863d3e36d/dashboard/config/linux/upstream-arm64-kasan.config#L509
> > > There are a number of other timeouts raised as well, some as high as
> > > 420 seconds.
> >
> > I see, I'll try with these settings and see if I can still hit the soft
> > lockup messages.
>
> Still getting soft lockup messages even with the new timeout settings:
>
> [  462.663766] watchdog: BUG: soft lockup - CPU#2 stuck for 430s! [systemd-udevd:168]
> [  462.755758] watchdog: BUG: soft lockup - CPU#3 stuck for 430s! [systemd-udevd:171]
> [  924.663765] watchdog: BUG: soft lockup - CPU#2 stuck for 861s! [systemd-udevd:168]
> [  924.755767] watchdog: BUG: soft lockup - CPU#3 stuck for 861s! [systemd-udevd:171]

The lockups are expected if you're hitting the TCG bug I linked. Try
to pass '-enable-kvm' to the inner qemu instance (my bad if you
already have), assuming that's somehow easy to do.

Thanks,
-- Marco