Messages in this thread | | | Date | Thu, 21 Sep 2006 01:13:33 -0700 | Subject | Re: [PATCH] move put_task_struct() reaping into a thread [Re: 2.6.18-rt1] | From | Bill Huey (hui) <> |
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On Thu, Sep 21, 2006 at 09:56:33AM +0200, Ingo Molnar wrote: > * Bill Huey <billh@gnuppy.monkey.org> wrote: > > > [...] If the upstream kernel used RCU function in a task allocation or > > task struct reading in the first place then call_rcu() would be a > > clear choice. However, I didn't see it used in that way (I could be > > wrong) [...] > > it was RCU-ified briefly but then it was further improved to direct > freeing, because upstream _can_ free it directly.
Unfortunately, this is a problem with -rt patch and the lock ordering in this system when you have to call a memory allocator within an atomic critical section. I fully accept this as part of what goes into making a kernel preemptive and I'm ok with it. Not many folks know about the special case locking rules in the -rt kernel so this might be new to various folks.
If you're looking for validation of this technique from me and an ego stroking, then you have it from me. :)
Fortunately, it's in a non-critical place so this should *not* be too much of a problem, but I've already encountered oddies trying to allocate a pool of entities for populating a free list under an atomic critical section of some sort for some code I've been writing. This is a significant problem with kernel coding in -rt, but I can't say what the general solution is other than making the memory allocators non-preemptible by reverting the locks back to raw spinlocks, etc... using lock-break, who knows. I'm ok with the current scenario, but this could eventually be a larger problem.
bill
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