linux-kernel - Re: [PATCH] relay: avoid relay_open_buf inproperly fails in buffer-only mode

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Message-ID: <2f93789c-e931-452a-9b42-43c3254b626f@linux.alibaba.com>
Date: Fri, 15 Mar 2024 11:22:53 +0800
From: Philo Lu <lulie@...ux.alibaba.com>
To: zhangzhengming <zhang.zhengming@....com>
Cc: akpm@...ux-foundation.org, alibuda@...ux.alibaba.com,
 dust.li@...ux.alibaba.com, gregkh@...uxfoundation.org,
 guwen@...ux.alibaba.com, hengqi@...ux.alibaba.com, kunyu@...china.com,
 linux-kernel@...r.kernel.org, nabijaczleweli@...ijaczleweli.xyz,
 xuanzhuo@...ux.alibaba.com, zhao_lei1@...erun.com, zhou.kete@....com
Subject: Re: [PATCH] relay: avoid relay_open_buf inproperly fails in
 buffer-only mode



On 2024/3/15 10:39, zhangzhengming wrote:
>> diff --git a/kernel/relay.c b/kernel/relay.c
>> index a8e90e98bf2c..0d8b8325530a 100644
>> --- a/kernel/relay.c
>> +++ b/kernel/relay.c
>> @@ -391,12 +391,13 @@ static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
>>   			goto free_buf;
>>   		relay_set_buf_dentry(buf, dentry);
>>   	} else {
>> -		/* Only retrieve global info, nothing more, nothing less */
>> +		/* In buffer-only mode, relay_open_buf is called with
>> +		 * filename=NULL, but create_buf_file is still needed to
>> +		 * retrieve is_global info. So dentry should be NULL here.
>> +		 */
>>   		dentry = chan->cb->create_buf_file(NULL, NULL,
>>   						   S_IRUSR, buf,
>>   						   &chan->is_global);
>> -		if (IS_ERR_OR_NULL(dentry))
>> -			goto free_buf;
>>   	}
>>   
>>    	buf->cpu = cpu;
> I suggest replacing IS_ERR_OR_NULL with IS_ERR instead of removing it due to the possibility of create_buf_file callback returning an error.
> 

This would be fine. AFAICT the return value here is un-important. So 
reverting to `WARN_ON(dentry)` maybe another choice.