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

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Message-Id: <20230901072626.278880-1-nashuiliang@gmail.com>
Date:   Fri,  1 Sep 2023 15:26:26 +0800
From:   Chuang Wang <nashuiliang@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Chuang Wang <nashuiliang@...il.com>, 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: [PATCH] tracing: Fix the unusable problem caused by non-empty pipe_cpumask

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.

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