Matt Helsley wrote: > On Thu, Nov 05, 2009 at 07:14:11PM -0500, Bill Davidsen wrote: > >> Li Zefan wrote: >> >>> Bill Davidsen wrote: >>> >>> >>>> Li Zefan wrote: >>>> >>>> >>>>> Liu Aleaxander wrote: >>>>> >>>>> >>>>>> From: Liu Aleaxander <Aleaxander@xxxxxxxxx> >>>>>> Date: Wed, 4 Nov 2009 09:27:06 +0800 >>>>>> Subject: [PATCH] Fixes the un-paired cgroup lock problem >>>>>> >>>>>> In cgroup_lock_live_group, it locks the cgroup by mutex_lock, while >>>>>> in the >>>>>> cgroup_tasks_write, it unlock it by cgroup_unlock. Even though they are >>>>>> equal, but I do think we should make it pair. >>>>>> >>>>>> BTW, should we replace others with cgroup_lock and cgroup_unlock? >>>>>> Since we already have a wrapper one and it's meaningful. >>>>>> >>>>>> >>>>>> >>>>> Before I read the email body, I thought there is a bug where >>>>> there is a lock without unlock or vise versa. >>>>> >>>>> I agree the case here can be called "unpaired", but I'm not >>>>> convinced this patch is needed. The code is not buggy or >>>>> confusing. So the patch neither fixes a bug nor make the code >>>>> more readable. >>>>> >>>>> >>>>> >>>> I would say it fixes a bug, the one that would be introduced when the >>>> two methods are no longer compatible and essentially two names for the >>>> same thing. And while you may know the code so well that you knew >>>> without looking that this was (currently) okay, there will be lots of >>>> eyes on this code over the years, I think most people would find use of >>>> cgroup_lock to lock the cgroup a LOT more readable. >>>> >>>> While you can't go back in time to murder your grandfather, it creates >>>> no paradox to fix a bug before someone writes it. >>>> >>>> >>>> >>> cgroup_lock() is not necessarily more readable than mutex_lock(&cgroup_mutex), >>> at least the former doesn't tell you the lock is a spin_lock or a mutex. >>> >>> >>> >> That's the point, cgroup_lock() is an abstraction, you want to lock the >> cgroup, you call the macro, the macro handles the details, and if >> thinking (or the most common cache configurations) change, the code >> still works. >> > > Except it doesn't really "lock the cgroup" as you've been saying -- else > it would take the cgroup to lock as a parameter. Instead it locks > "all cgroups". Clearly there's room for misunderstanding even with > cgroup_lock(). > Now that seems to be a good argument for better naming of the locks, something like lock_all_cgroups or whatever. It does seem to support my point of using a macro named after "waht operation you are doing" rather than "how you are doing it today." Thanks for the clarification. -- Bill Davidsen <davidsen@xxxxxxx> Unintended results are the well-earned reward for incompetence. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
