linux-kernel - Re: [PATCH] perf lock contention: Add a missing NULL check

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Date: Tue, 2 Apr 2024 13:42:05 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Ian Rogers <irogers@...gle.com>, Kan Liang <kan.liang@...ux.intel.com>, 
	Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, 
	LKML <linux-kernel@...r.kernel.org>, linux-perf-users@...r.kernel.org, 
	Song Liu <song@...nel.org>, bpf@...r.kernel.org
Subject: Re: [PATCH] perf lock contention: Add a missing NULL check

On Tue, Apr 2, 2024 at 12:45 PM Arnaldo Carvalho de Melo
<acme@...nel.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 == (void *)lock)
> >   265: (79) r1 = *(u64 *)(r0 +2624)     ; frame1: R0_w=trusted_ptr_task_struct(off=0,imm=0) R1_w=rcu_ptr_or_null_sighand_struct(off=0,imm=0)
> >   266: (b7) r2 = 0                      ; frame1: R2_w=0
> >   267: (0f) r1 += r2
> >   R1 pointer arithmetic on rcu_ptr_or_null_ prohibited, null-check it first
> >   processed 164 insns (limit 1000000) max_states_per_insn 1 total_states 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@...nel.org>
>
> Acked-by: Arnaldo Carvalho de Melo <acme@...hat.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