Tejun Heo <htejun@xxxxxxxxx> writes: >> To do that I believe we would need to ensure sysfs does not use >> the inode->i_mutex lock except to keep the VFS layer out. Allowing us >> to safely change the directory structure, without holding it. > > I don't think sysfs is depending on i_mutex anymore but I need to go > through the code to make sure. The vfs still does. So at least for directory tree manipulation we need to hold i_mutex before we grab sysfs_mutex. I think that means we need to unscramble the whole set of locking order issues. In lookup we have: local_vfs_lock -> fs_global_lock In modifications we have: fs_global_lock -> local_vfs_lock Which is the definition of a lock ordering problem. Currently we play jump through some significant hoops to keep things in local_vfs_lock -> fs_global_lock order. If we also take the rename_mutex on directory adds and deletes we may be able to keep jumping through those hoops. However I expect we would be in a much better situation if we could figure out how to avoid the problem. It looks like the easy way to handle this is to make the sysfs_dirent list rcu protected. Which means we can fix our lock ordering problem without VFS modifications. Allowing the locking to always be: sysfs_mutex ... i_mutex. After that it would be safe and a good idea to have unshared inodes between superblocks, just so we don't surprise anyone making generic VFS assumptions. Eric _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
