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Date: Fri, 05 Oct 2007 02:05:32 -0700 From: Jeremy Fitzhardinge <jeremy@...p.org> To: Keir Fraser <Keir.Fraser@...source.com> CC: Andrew Morton <akpm@...ux-foundation.org>, Hugh Dickens <hugh@...itas.com>, David Rientjes <rientjes@...gle.com>, Zachary Amsden <zach@...are.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Rusty Russell <rusty@...tcorp.com.au>, Andi Kleen <ak@...e.de>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: race with page_referenced_one->ptep_test_and_clear_young and pagetable setup/pulldown 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). J - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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