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:   Tue, 29 Jun 2021 18:25:33 +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 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:
> > > On Sun, 27 Jun 2021 at 17:34, Jiri Olsa <jolsa@...hat.com> wrote:
> > > >
> > > > On Tue, Feb 02, 2021 at 01:50:02PM +0000, Brendan Jackman wrote:
[snip]
> > > Hmm, is the test prog from atomic_bounds.c getting JITed there (my
> > > dumb guess at what '0xc0000000119efb30 (unreliable)' means)? That
> > > shouldn't happen - should get 'eBPF filter atomic op code %02x (@%d)
> > > unsupported\n' in dmesg instead. I wonder if I missed something in
> > > commit 91c960b0056 (bpf: Rename BPF_XADD and prepare to encode other
>
> I see that for all the other atomics tests:
>
> [root@...-p9z-07-lp1 bpf]# ./test_verifier 21
> #21/p BPF_ATOMIC_AND without fetch FAIL
> Failed to load prog 'Unknown error 524'!
> verification time 32 usec
> stack depth 8
> processed 10 insns (limit 1000000) max_states_per_insn 0 total_states 1 peak_states 1 mark_read 1
> Summary: 0 PASSED, 0 SKIPPED, 2 FAILED

Hm that's also not good - failure to JIT shouldn't mean failure to
load. Are there other test_verifier failures or is it just the atomics
ones?

> console:
>
>         [   51.850952] eBPF filter atomic op code db (@2) unsupported
>         [   51.851134] eBPF filter atomic op code db (@2) unsupported
>
>
> [root@...-p9z-07-lp1 bpf]# ./test_verifier 22
> #22/u BPF_ATOMIC_AND with fetch FAIL
> Failed to load prog 'Unknown error 524'!
> verification time 38 usec
> stack depth 8
> processed 14 insns (limit 1000000) max_states_per_insn 0 total_states 1 peak_states 1 mark_read 1
> #22/p BPF_ATOMIC_AND with fetch FAIL
> Failed to load prog 'Unknown error 524'!
> verification time 26 usec
> stack depth 8
> processed 14 insns (limit 1000000) max_states_per_insn 0 total_states 1 peak_states 1 mark_read 1
>
> console:
>         [  223.231420] eBPF filter atomic op code db (@3) unsupported
>         [  223.231596] eBPF filter atomic op code db (@3) unsupported
>
> ...
>
>
> but no such console output for:
>
> [root@...-p9z-07-lp1 bpf]# ./test_verifier 24
> #24/u BPF_ATOMIC bounds propagation, mem->reg OK
>
>
> > > 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?