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Subject: Re: [PATCH] tracing: fix incorrect tracer freeing when opening
 tracing pipe
To:     Steven Rostedt <rostedt@goodmis.org>
References: <1550060946-45984-1-git-send-email-yi.zhang@huawei.com>
 <20190213083635.36f4762e@gandalf.local.home>
CC:     <mingo@redhat.com>, <linux-kernel@vger.kernel.org>,
        <miaoxie@huawei.com>
From:   "zhangyi (F)" <yi.zhang@huawei.com>
Message-ID: <ed080680-ddac-3e99-720e-a8371fce5ab6@huawei.com>
Date:   Sat, 16 Feb 2019 19:19:03 +0800
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On 2019/2/13 21:36, Steven Rostedt Wrote:
> On Wed, 13 Feb 2019 20:29:06 +0800
> "zhangyi (F)" <yi.zhang@huawei.com> wrote:
> 
>> Commit d716ff71dd12 ("tracing: Remove taking of trace_types_lock in
>> pipe files") use the current tracer instead of the copy in
>> tracing_open_pipe(), but it forget to remove the freeing sentence in
>> the error path.
>>
>> Fixes: d716ff71dd12 ("tracing: Remove taking of trace_types_lock in pipe files")
> 
> Thanks.
> 
> As this is harmless (frees to NULL is ok, and iter is allocated with
> kzalloc()), I'm going to just add this for the next merge window.
> 

This patch patch want to remove kfree(iter->trace) instead of kfree(iter),
which is set by tr->current_trace and probably not allocated dynamically.
So if we kfree such tracer in the error path, it will lead to BUG_ON.

Thanks，
Yi.

> 
>> Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
>> ---
>>  kernel/trace/trace.c | 1 -
>>  1 file changed, 1 deletion(-)
>>
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index c521b73..b583ff7 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -5624,7 +5624,6 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
>>  	return ret;
>>  
>>  fail:
>> -	kfree(iter->trace);
>>  	kfree(iter);
>>  	__trace_array_put(tr);
>>  	mutex_unlock(&trace_types_lock);
> 
> 
> .
>