From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: Re: [PATCH v7] blktrace: Fix potentail deadlock between delete & sysfs ops Date: Wed, 20 Sep 2017 15:05:36 -0400 Message-ID: <76cc6fea-fd1a-04fb-b18b-04ea5d69dde9@redhat.com> References: <1505928371-27829-1-git-send-email-longman@redhat.com> <20170920173552.GA14611@infradead.org> Mime-Version: 1.0 Content-Transfer-Encoding: 8BIT Return-path: In-Reply-To: <20170920173552.GA14611-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org> Content-Language: en-US Sender: linux-nilfs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Christoph Hellwig Cc: Jens Axboe , Steven Rostedt , Ingo Molnar , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-nilfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cluster-devel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Bart Van Assche 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 -- To unsubscribe from this list: send the line "unsubscribe linux-nilfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html