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From:   Jiri Olsa <olsajiri@gmail.com>
Date:   Thu, 6 Oct 2022 20:58:54 +0200
To:     Sumanth Korikkar <sumanthk@linux.ibm.com>
Cc:     tip-bot2@linutronix.de, linux-kernel@vger.kernel.org,
        linux-tip-commits@vger.kernel.org, namhyung@kernel.org,
        peterz@infradead.org, x86@kernel.org, iii@linux.ibm.com,
        gor@linux.ibm.com, hca@linux.ibm.com, svens@linux.ibm.com,
        tmricht@linux.ibm.com, bpf@vger.kernel.org
Subject: Re: [PATCH] Re: [tip: perf/core] perf: Use sample_flags for raw_data
Message-ID: <Yz8lbkx3HYQpnvIB@krava>
References: <166434824149.401.4361243714612738808.tip-bot2@tip-bot2>
 <20221006160044.3397237-1-sumanthk@linux.ibm.com>
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On Thu, Oct 06, 2022 at 06:00:44PM +0200, Sumanth Korikkar wrote:
> Hi,
> 
> This causes segfaults.
> 
> Steps to recreate:
> *  Run ./samples/bpf/trace_output
> BUG pid 9 cookie 1001000000004 sized 4
> BUG pid 9 cookie 1001000000004 sized 4
> BUG pid 9 cookie 1001000000004 sized 4
> Segmentation fault (core dumped)
> 
> Problem:
> * The following commit sets data->raw to NULL, when the raw data is not filled
> by PMU driver. This leads to stale data.
>    
> * raw data could also be filled by bpf_perf_event_output(), bpf_event_output()
> ...
>  686         perf_sample_data_init(sd, 0, 0);
>  687         sd->raw = &raw;
>  688
>  689         err = __bpf_perf_event_output(regs, map, flags, sd);
> ...
> 
> * The below patch eliminates segfaults. However, contradicts with
> the description mentioned in this commit (Filled by only PMU driver).

hi,
could you please resend the patch with formal changelog and Fixes tag?

thanks,
jirka

>   
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 49fb9ec8366d..1ed08967fb97 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -687,6 +687,7 @@ BPF_CALL_5(bpf_perf_event_output, struct pt_regs *, regs, struct bpf_map *, map,
>  
>         perf_sample_data_init(sd, 0, 0);
>         sd->raw = &raw;
> +       sd->sample_flags |= PERF_SAMPLE_RAW;
>  
>         err = __bpf_perf_event_output(regs, map, flags, sd);
>  
> @@ -745,6 +746,7 @@ u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size,
>         perf_fetch_caller_regs(regs);
>         perf_sample_data_init(sd, 0, 0);
>         sd->raw = &raw;
> +       sd->sample_flags |= PERF_SAMPLE_RAW;
>  
>         ret = __bpf_perf_event_output(regs, map, flags, sd);
>  out:
>   
> --
> Thanks,
> Sumanth