linux-kernel - Re: [PATCH] tracing: Fix the unusable problem caused by non-empty pipe

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Message-Id: <20230901230206.9bf0250291acd7bfbde46b53@kernel.org>
Date:   Fri, 1 Sep 2023 23:02:06 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Chuang Wang <nashuiliang@...il.com>
Cc:     stable@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Zheng Yejian <zhengyejian1@...wei.com>,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: Fix the unusable problem caused by non-empty
 pipe_cpumask

On Fri,  1 Sep 2023 15:26:26 +0800
Chuang Wang <nashuiliang@...il.com> wrote:

> There is a problem in the linux-6.5 when I execute the following
> command:
> 
>  $ perf ftrace -t irqsoff
>  failed to open trace_pipe
> 
> At the same time, when I open this file, the same error occurs.
> 
> Therefore, after carefully looking at the code, the open function of
> 'trace_pipe' returns -EBUSY in open_pipe_on_cpu() because no clearing
> operation was performed when 'trace_array->pipe_cpumask' was allocated.
> 
> With this patch, Use zalloc_cpumask_var() to ensure that
> 'trace_array->pipe_cpumask' is reset to 0 when allocated.

Good catch. This looks good to me.

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

> 
> Cc: stable@...r.kernel.org
> Fixes: c2489bb7e6be ("tracing: Introduce pipe_cpumask to avoid race on trace_pipes")
> Signed-off-by: Chuang Wang <nashuiliang@...il.com>
> ---
>  kernel/trace/trace.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index d8233d34b5a0..c0b8a72f3466 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -9461,7 +9461,7 @@ static struct trace_array *trace_array_create(const char *name)
>  	if (!alloc_cpumask_var(&tr->tracing_cpumask, GFP_KERNEL))
>  		goto out_free_tr;
>  
> -	if (!alloc_cpumask_var(&tr->pipe_cpumask, GFP_KERNEL))
> +	if (!zalloc_cpumask_var(&tr->pipe_cpumask, GFP_KERNEL))
>  		goto out_free_tr;
>  
>  	tr->trace_flags = global_trace.trace_flags & ~ZEROED_TRACE_FLAGS;
> @@ -10406,7 +10406,7 @@ __init static int tracer_alloc_buffers(void)
>  	if (trace_create_savedcmd() < 0)
>  		goto out_free_temp_buffer;
>  
> -	if (!alloc_cpumask_var(&global_trace.pipe_cpumask, GFP_KERNEL))
> +	if (!zalloc_cpumask_var(&global_trace.pipe_cpumask, GFP_KERNEL))
>  		goto out_free_savedcmd;
>  
>  	/* TODO: make the number of buffers hot pluggable with CPUS */
> -- 
> 2.39.2
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>