linux-kernel - Re: [BUG soft lockup] Re: [PATCH bpf-next v3] bpf: Propagate stack bounds to registers in atomics w/ BPF

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Date:   Wed, 30 Jun 2021 12:34:58 +0200
From:   Brendan Jackman <jackmanb@...gle.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Florent Revest <revest@...omium.org>,
        John Fastabend <john.fastabend@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Sandipan Das <sandipan@...ux.ibm.com>
Subject: Re: [BUG soft lockup] Re: [PATCH bpf-next v3] bpf: Propagate stack
 bounds to registers in atomics w/ BPF_FETCH

On Tue, 29 Jun 2021 at 23:09, Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Tue, Jun 29, 2021 at 06:41:24PM +0200, Jiri Olsa wrote:
> > On Tue, Jun 29, 2021 at 06:25:33PM +0200, Brendan Jackman wrote:
> > > On Tue, 29 Jun 2021 at 18:04, Jiri Olsa <jolsa@...hat.com> wrote:
> > > > On Tue, Jun 29, 2021 at 04:10:12PM +0200, Jiri Olsa wrote:
> > > > > On Mon, Jun 28, 2021 at 11:21:42AM +0200, Brendan Jackman wrote:

> > > > > > atomics in .imm). Any idea if this test was ever passing on PowerPC?
> > > > > >
> > > > >
> > > > > hum, I guess not.. will check
> > > >
> > > > nope, it locks up the same:
> > >
> > > Do you mean it locks up at commit 91c960b0056 too?

Sorry I was being stupid here - the test didn't exist at this commit

> > I tried this one:
> >   37086bfdc737 bpf: Propagate stack bounds to registers in atomics w/ BPF_FETCH
> >
> > I will check also 91c960b0056, but I think it's the new test issue

So yeah hard to say whether this was broken on PowerPC all along. How
hard is it for me to get set up to reproduce the failure? Is there a
rootfs I can download, and some instructions for running a PowerPC
QEMU VM? If so if you can also share your config and I'll take a look.

If it's not as simple as that, I'll stare at the code for a while and
see if anything jumps out.