Messages in this thread | | | From | Linus Torvalds <> | Date | Thu, 24 Nov 2011 20:02:18 -0800 | Subject | Re: [PATCH UPDATED 03/10] threadgroup: extend threadgroup_lock() to cover exit and exec |
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On Thu, Nov 24, 2011 at 2:50 PM, Tejun Heo <tj@kernel.org> wrote: > > Linus, this is something being scheduled for the next merge window. > It extends threadgroup locking which cgroup used to do to exclude only > fork path so that it includes exit and exec paths. threadgroup > locking is used by cgroup to implement process-scope cgroup migration. > > Migration happens in multiple steps, at each of which the matching > method of each cgroup plugin is called. When a whole process is being > migrated, methods being called at those different steps expect to see > consistent image of the thread group.
Ugh.
I see why you want to do this, but I really don't much like some of it.
I've got a few questions:
- do you even *need* two separate locks at all? If you extend the threadgroup_fork_lock to cover exec/exit too (and rename it), then why does that separate cred_guard_mutex make sense at all?
Taking two locks for the common exit case seems disgusting. What do the separate locks buy us?
- could we possible avoid the lock(s) entirely for the single-threaded case? The fact that ptrace wants to serialize makes me say "maybe we can't avoid it", but I thought I'd ask. Even if we do need/want two separate locks, do we really want to take them both for the case that shouldn't really need even a single one?
Hmm? Simplifying the locking rules is always a good idea, and I think this seems to make some of it more straightforward, but at the same time I shudder when I look at some of the patches in the series that nest locking three locks deep. Ugh.
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