From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joel Becker Date: Tue, 20 May 2008 14:56:39 -0700 Subject: [Ocfs2-devel] [RFC][PATCH 0/3] configfs: Make nested default groups lockdep-friendly In-Reply-To: <20080520095810.1d50d247@infradead.org> References: <20080520163320.025971210@kerlabs.com> <20080520095810.1d50d247@infradead.org> Message-ID: <20080520215639.GG26609@mail.oracle.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Arjan van de Ven Cc: Louis Rilling , linux-kernel@vger.kernel.org, ocfs2-devel@oss.oracle.com On Tue, May 20, 2008 at 09:58:10AM -0700, Arjan van de Ven wrote: > On Tue, 20 May 2008 18:33:20 +0200 > Louis Rilling wrote: > > > The following patches fix lockdep warnings resulting from (correct) > > recursive locking in configfs. > > > > ... > > > > Since lockdep does not handle such correct recursion, the idea is to > > insert lockdep_off()/lockdep_on() for inode mutexes as soon as the > > level of recursion of the I_MUTEX_PARENT -> I_MUTEX_CHILD dependency > > pattern increases. > > I'm... not entirely happy with such a solution ;( > > there must be a better one. We're trying to find it. I really appreciate Louis taking the time to approach the issue. His first pass was to add 1 to MUTEX_CHILD for each level of recursion. This has a very tight limit (4 or 5 levels), but probably covers all users that exist and perhaps all that ever will exist. However, it means passing the lockdep annotation level throughout the entire call chain across multiple files. It was definitely less readable. This approach takes a different tack - it's very readable, but it assumes that the currently correct locking will always remain so - a particular invariant that lockdep exists to verify :-) Louis, what about sticking the recursion level on configfs_dirent? That is, you could add sd->s_level and then use it when needed. THis would hopefully avoid having to pass the level as an argument to every function. Then we can go back to your original scheme. If they recurse too much and hit the lockdep limit, just rewind everything and return -ELOOP. Joel -- Dort wo man B?cher verbrennt, verbrennt man am Ende auch Mensch. (Wherever they burn books, they will also end up burning people.) - Heinrich Heine Joel Becker Principal Software Developer Oracle E-mail: joel.becker at oracle.com Phone: (650) 506-8127