On Mon, Apr 02, 2007 at 04:59:43AM +0900, Tejun Heo wrote: > > Dependencies between sysfs/kobject objects are clearer now and I think > I got the locking and referencing correct. This patch immediately > fixes 'sysfs attr grabbing the wrong kobject and module' problem - > sysfs and module lifetimes are unrelated now. We can drop > half-working attr->owner. > > * A sysfs node no longer hold reference to its kobject. It just > attaches itself to the kobject on creation and detaches on deletion. > > * For a dir node, sysfs_dirent no longer directly points to kobject. > It points to sysfs_dir which contains pointer to kobject and a rwsem > to protect it. > > * An open file doesn't hold a reference to kobject. It holds a > reference to sysfs_dirent. kobject pointer is verified and > show/store are performed with rwsem read-locked. Deletion > disconnects the sysfs from its kobject while the rwsem is > write-locked. This mechanism replaces buffer orphaning and kobject > validation during open. Ah, very nice. > * attr ops is determined on sysfs node creation not on open. This is > a step toward making kobject opaque in sysfs. > > * bin files are handled similarly but mmap makes the open file hold > reference to the kobject till it's closed. Any better ideas? This is probably needed, and might be acceptable, and I think we can live with it as there is only a very small number of sysfs files that fall into this category. > * symlink is reimplemented in terms of sysfs_dirents instead of > kobjects. sysfs_dirent->s_parent is added and each sysfs_dirent > holds reference to its parent. Currently walking up the tree > requires read locking and unlocking sysfs_dir at each level. This > can be removed if name is added to sysfs_dirent. > > * As kobject can be disconnected anytime and sysfs code still needs to > look follow dentry link in kobject, kobject->dentry is protected by > dcache_lock. Once kobject becomes opaque to sysfs, this hack can go > away. All in all, making kobject completely opaque in sysfs isn't > too far away after this patch although it would require mass code > update. What would need to be updated after this? > What do you think about this approach? If it's acceptable, I'll test > further and split the patch into logical steps to get it reviewed > better. At first glance, I think it looks fine, but Maneesh is the one who understands this code better than anyone, so I would like to get his opinion on it. I think you should start splitting it all up into steps, which will help us review it a whole lot easier, as overall, I think this is a very worthy goal. thanks so much for doing this work, greg k-h - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
