Messages in this thread | | | Date | Fri, 05 Oct 2007 02:05:32 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: race with page_referenced_one->ptep_test_and_clear_young and pagetable setup/pulldown |
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Keir Fraser wrote: > > Hang on! How is the access unlocked? By my reading > page_referenced_one()->page_check_address()->spin_lock(pte_lockptr()). >
Ah, OK. I'd overlooked that.
> The problem here is most likely insufficient locking in the pin/unpin > table-walking code, in light of the fact that you are probably running > with > per-page spinlocks (SPLIT_PTLOCK_CPUS). Because we nobble that option > in our > own kernel ports it suffices to take the page_table_lock when doing the > walk-[un]pin-remap routine. This is *not* true with SPLIT_PTLOCK_CPUS. >
Hm, I see.
> Fortuitously, Jan Beulich has a patch to fix this. It's not going to be > directly applicable to 2.6.23-rc series, but should be easily ported: > <http://lists.xensource.com/archives/html/xen-devel/2007-03/msg01200.html>. >
OK, I can use that.
Andi says: > Do I misread that patch or does it really walk the complete address > space and try to take all possible locks? Isn't that very slow? >
That's pretty much what it has to do. Pinning/unpinning walks the whole pagetable anyway, so it shouldn't be much more expensive. And they're relatively rare operations (fork, exec, exit).
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