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From: Namhyung Kim <namhyung@kernel.org>
Date: Tue, 2 Apr 2024 13:42:05 -0700
Message-ID: <CAM9d7ci7a2dbn1cz-OBkYF7P1fFA3yoBMuTzXRx=KP-yEnyfnQ@mail.gmail.com>
Subject: Re: [PATCH] perf lock contention: Add a missing NULL check
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Ian Rogers <irogers@google.com>, Kan Liang <kan.liang@linux.intel.com>, 
	Jiri Olsa <jolsa@kernel.org>, Adrian Hunter <adrian.hunter@intel.com>, 
	Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>, 
	LKML <linux-kernel@vger.kernel.org>, linux-perf-users@vger.kernel.org, 
	Song Liu <song@kernel.org>, bpf@vger.kernel.org
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On Tue, Apr 2, 2024 at 12:45=E2=80=AFPM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> On Tue, Apr 02, 2024 at 11:45:43AM -0700, Namhyung Kim wrote:
> > I got a report for a failure in BPF verifier on a recent kernel with
> > perf lock contention command.  It checks task->sighand->siglock without
> > checking if sighand is NULL or not.  Let's add one.
> >
> >   ; if (&curr->sighand->siglock =3D=3D (void *)lock)
> >   265: (79) r1 =3D *(u64 *)(r0 +2624)     ; frame1: R0_w=3Dtrusted_ptr_=
task_struct(off=3D0,imm=3D0) R1_w=3Drcu_ptr_or_null_sighand_struct(off=3D0,=
imm=3D0)
> >   266: (b7) r2 =3D 0                      ; frame1: R2_w=3D0
> >   267: (0f) r1 +=3D r2
> >   R1 pointer arithmetic on rcu_ptr_or_null_ prohibited, null-check it f=
irst
> >   processed 164 insns (limit 1000000) max_states_per_insn 1 total_state=
s 15 peak_states 15 mark_read 5
> >   -- END PROG LOAD LOG --
> >   libbpf: prog 'contention_end': failed to load: -13
> >   libbpf: failed to load object 'lock_contention_bpf'
> >   libbpf: failed to load BPF skeleton 'lock_contention_bpf': -13
> >   Failed to load lock-contention BPF skeleton
> >   lock contention BPF setup failed
> >   lock contention did not detect any lock contention
> >
> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
>
> Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
>
> Are you going to have this merged into perf-tools?
>
> A Fixes: tag isn't perhaps needed as it worked in the past?

Fixes: 1811e82767dcc ("perf lock contention: Track and show siglock
with address")

It was introduced in v6.4 and it should be fine to have this
even without the error.  I'll queue it to perf-tools.

Thanks,
Namhyung