Hello, On Tue, Oct 29, 2013 at 10:29:43PM -0700, Eric W. Biederman wrote: > I never actually looked deeply into it, and I was working from several > year old memory and a quick skim of the patch when I asked the question. > > The protection we have previous to this patch is that syfs_remove_dir is > only sane to call once. > > Which makes the code that does: > if (!dir_sd) > return; > in __sysfs_remove_dir very suspicious. I expect we want a > WARN_ON(!dir_sd);
It was always like that, probably in the same spirit as kfree() taking NULL so that it can be easier, for example, in init failure paths. > But the entire directory removal process and working on sysfs stopped > being fun before I managed to get that cleaned up. And unless I missed > something go by Tejun is going to go generalize this thing before this > bit gets cleaned up. Sigh. I kept the same behavior for kernfs_remove(). I don't think it's something we explicitly want to clean up tho? It's an acceptable behavior. > On an equally bizarre note. I don't understand why we have a separate > spinlock there. Looks... Sigh. We use a different lock from > everything as a premature optimization so that sysfs_remove_dir could be > modified to just take a sysfs_dirent, and all of the kobject handling > could be removed. > > Sigh. It was never in my way and while I was working on the code that > there was a good locking reason for doing that silly thing. Umm... you got it completely wrong. It's there to address a race condition between removal and symlinking and has nothing to do with optimization. The current odd looking locking on removal side serves a purpose in making it clear that it isn't synchronizing concurrent removal calls. Maybe we should rename the lock to sysfs_symlink_target_lock and add fat comments on both sides? Or we can make it a mutex and exclude the entire removal and symlinking, which would probably easier to follow. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
