DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com B4EFE7E426
Subject: Re: [PATCH v7] blktrace: Fix potentail deadlock between delete &
 sysfs ops
To: Christoph Hellwig <hch@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>, Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org,
        linux-nilfs@vger.kernel.org, cluster-devel@redhat.com,
        Bart Van Assche <Bart.VanAssche@wdc.com>
References: <1505928371-27829-1-git-send-email-longman@redhat.com>
 <20170920173552.GA14611@infradead.org>
From: Waiman Long <longman@redhat.com>
Organization: Red Hat
Message-ID: <76cc6fea-fd1a-04fb-b18b-04ea5d69dde9@redhat.com>
Date: Wed, 20 Sep 2017 15:05:36 -0400
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.2.0
MIME-Version: 1.0
In-Reply-To: <20170920173552.GA14611@infradead.org>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8BIT
Content-Language: en-US
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1272
Lines: 27

On 09/20/2017 01:35 PM, Christoph Hellwig wrote:
>> +/*
>> + * When reading or writing the blktrace sysfs files, the references to the
>> + * opened sysfs or device files should prevent the underlying block device
>> + * from being removed. So no further delete protection is really needed.
>> + *
>> + * Protection from multiple readers and writers accessing blktrace data
>> + * concurrently is still required. The bd_mutex was used for this purpose.
>> + * That could lead to deadlock with concurrent block device deletion and
>> + * sysfs access. As a result, a new blk_trace_mutex is now added to be
>> + * used solely by the blktrace code.
>> + */
> Comments about previous locking schemes really don't have a business
> in the code - those are remarks for the commit logs.  And in general
> please explain the locking scheme near the data that they proctect
> it, as locks should always protected data, not code and the comments
> should follow that.

It seems to be a general practice that we don't put detailed comments in
the header files. The comment was put above the function with the first
instance of the blk_trace_mutex. Yes, I agree that talking about the
past history may not be applicable here. I will keep that in mind in the
future.

Thanks,
Longman