Messages in this thread | | | Date | Thu, 30 Apr 2009 10:20:14 -0700 | From | Joel Becker <> | Subject | Re: [PATCH 2/2] configfs: Rework configfs_depend_item() locking and make lockdep happy |
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On Thu, Apr 30, 2009 at 11:18:28AM +0200, Louis Rilling wrote: > On 29/04/09 11:52 -0700, Joel Becker wrote: > > On Wed, Jan 28, 2009 at 07:18:33PM +0100, Louis Rilling wrote: > > > configfs_depend_item() recursively locks all inodes mutex from configfs root to > > > the target item, which makes lockdep unhappy. The purpose of this recursive > > > locking is to ensure that the item tree can be safely parsed and that the target > > > item, if found, is not about to leave. > > > > > > This patch reworks configfs_depend_item() locking using configfs_dirent_lock. > > > Since configfs_dirent_lock protects all changes to the configfs_dirent tree, and > > > protects tagging of items to be removed, this lock can be used instead of the > > > inodes mutex lock chain. > > > This needs that the check for dependents be done atomically with > > > CONFIGFS_USET_DROPPING tagging. > > > > These patches are now in the 'lockdep' branch of the configfs > > tree. I'm planning to send them in the next merge window. I've made > > one change. > > > > > + * Note: items in the middle of attachment start with s_type = 0 > > > + * (configfs_new_dirent()), and configfs_make_dirent() (called from > > > + * create_dir()) sets s_type = CONFIGFS_DIR|CONFIGFS_USET_CREATING. In both > > > + * cases the item is ignored. Since s_type is an int, we rely on the CPU to > > > + * atomically update the value, without making configfs_make_dirent() take > > > + * configfs_dirent_lock. > > > > I've added configfs_dirent_lock in configfs_make_dirent(), > > because it is not safe at all to rely on the fact that s_type is an int. > > It's an atomic set on one CPU, but there's no guarantee that it's seen > > correctly on other CPUs. Plus, there's no real need for speed here. So > > we properly take configfs_dirent_lock around s_type in > > configfs_make_dirent(), and that ensures we see things correctly on SMP. > > Agreed, I was going to suggest something like this. Actually I'd push the > initialization of s_type down to configfs_new_dirent(), so that s_type either > is always NULL, or always shows the correct type of object.
0, not "NULL", but yeah I think that's a good plan.
Joel
--
"If at first you don't succeed, cover all traces that you tried." -Unknown
Joel Becker Principal Software Developer Oracle E-mail: joel.becker@oracle.com Phone: (650) 506-8127
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