Tejun Heo <tj@xxxxxxxxxx> writes: > Eric W. Biederman wrote: >>> I agree we should be heading this way but what happens to attributes >>> or directories living below the subdirectories? If it's gonna handle >>> recursive case, I think it better do it properly. I had patches of >>> similar effect. >> >> I do handle it properly. sysfs_get_one finds the deepest child of the >> first directory entry. Then I remove it. And I repeat until done. >> >> The locking is correct, something that is much more difficult to >> tell with your version. > > Why? :-) Because mine is all in a single place and there is no optimization to get locks I don't need. Unless I have misread your patch you are failing to get the i_mutex for child directories, if it possible to get it. Something that it is trivial to see that I always do correctly. Simply because the distance between the lock and where I depend on it is so small. >> By grabbing and dropping the sysfs_mutex things are simpler, and they >> get even simpler in future patches. >> >> Now looking at that code in detail there is a question of what happens if >> we add a directory entry while we are recursively deleting a directory. >> Neither your patch, my patch, nor the existing code handle that case >> (assuming the sysfs_dirent) was looked up before it is removed from it's >> parent directory. I expect another patch is called for to plug that >> theoretical gap. >> >> I expect the way to close that hole is to have an extra flag that says >> we are removing a directory entry and refuse to add if that flag is >> set. >> >> I would prefer to only remove empty directories. But when I >> instrumented things up I found cases where that does indeed happen. > > IIRC, my version did the whole thing while holding sysfs_mutex, so > it's safe against such races. I can't really see why ops like this > can't be atomic in sysfs. I don't really care how things are done but > please make it atomic. Nope. Holding the sysfs_mutex does not make you safe from such races. It actually makes you more prone to someone adding a directory entry to a deleted directory and not having it deleted. I have a chance of deleting the added directory entry. The problem is that sysfs_add_one takes to sysfs_dirents. The look up of the directory is done before we take the sysfs_mutex. So the sysfs_dirent could be grabbed at any time. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
