From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH 12/25] sysfs: Introduce sysfs_rename_mutex Date: Wed, 08 Aug 2007 17:23:11 +0900 Message-ID: <46B97D6F.8040504@suse.de> References: <11860582832964-git-send-email-htejun@gmail.com> <46B97C94.8090209@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <46B97C94.8090209@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Tejun Heo Cc: "Eric W. Biederman" , Greg KH , linux-kernel@vger.kernel.org, satyam@infradead.org, cornelia.huck@de.ibm.com, stern@rowland.harvard.edu, Linux Containers , gregkh@suse.de List-Id: containers.vger.kernel.org Tejun Heo wrote: > Hello, Eric. > > Eric W. Biederman wrote: >> Looking carefully at the rename code we have a subtle dependency >> that the structure of sysfs not change while we are performing >> a rename. If the parent directory of the object we are renaming >> changes while the rename is being performed nasty things could >> happen when we go to release our locks. >> >> So introduce a sysfs_rename_mutex to prevent this highly >> unlikely theoretical issue. > > Yeah, it's a theoretical issue. Rename/move implementation has always > depended on the parent structure not changing beneath it, but it's nice > to tighten up loose ends. > >> +DEFINE_MUTEX(sysfs_rename_mutex); > > Probably doesn't really matter but wouldn't a rwsem fit better? > >> @@ -774,7 +775,7 @@ static struct dentry *__sysfs_get_dentry(struct super_block *sb, struct sysfs_di >> * down from there looking up dentry for each step. >> * >> * LOCKING: >> - * Kernel thread context (may sleep) >> + * mutex_lock(sysfs_rename_mutex) > > LOCKING describes what locks should be held when entering the function, > so proper description would be something like... > > Kernel thread context, grabs sysfs_rename_mutex Oops, forget about the above. Thought the comment was added to sysfs_rename_dir(). -- tejun