Messages in this thread | | | From | (Eric W. Biederman) | Subject | Re: [PATCH] move put_task_struct() reaping into a thread [Re: 2.6.18-rt1] | Date | Wed, 27 Sep 2006 07:59:59 -0600 |
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Ingo Molnar <mingo@elte.hu> writes:
> * Eric W. Biederman <ebiederm@xmission.com> wrote: > >> Yes I am. The motivator would be the RT work but I don't see a reason >> why the it couldn't be put in the mainline kernel. If not at least we >> need the big fat comment in the mainline kernel that says >> put_task_struct must be safe to call with interrupts disabled. >> >> The way the code is structured now it deviates from the mainline >> kernel in more than just changing locking behavior. Which is what >> brought me into this conversation in the first place. So removing >> that point of discord would be good. > > well, this is one of those few cases (out of ~50,000 lock uses in the > kernel) where such a change was unavoidable: put_task_struct() is used > in the scheduler context-switch path. (see sched.c:finish_task_switch())
I had missed that was in a preempt disable path when I skimmed through the users.
> So that's why i first turned it into a separate, extra delayed-free via > the "desched thread", and later on picked up the RCUification from Paul > McKenney. The RCUification was the simpler (and hence easier to > maintain) change. There is no problem with putting this into the RCU > path on PREEMPT_RT, as this is a resource-freeing act. I.e. whatever > 'delay' there might be in RCU processing, it does not impact program > logic. I agree with you that on !PREEMPT_RT there's no reason to > complicate things with an extra layer of indirection.
I'm still wondering if we can move put_task_struct a little lower in the logic in the places where it is called, so it isn't called under a lock, or with preemption disabled. The only downside I see is that it might convolute the logic into unreadability.
In general I get nervous about calling big functions while holding locks.
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