From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Hugh Dickins <hughd@google.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>,
linuxppc-dev@lists.ozlabs.org,
Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: mmotm threatens ppc preemption again
Date: Mon, 21 Mar 2011 10:53:08 +1100 [thread overview]
Message-ID: <1300665188.2402.64.camel@pasglop> (raw)
In-Reply-To: <alpine.LSU.2.00.1103192041390.1592@sister.anvils>
On Sat, 2011-03-19 at 21:11 -0700, Hugh Dickins wrote:
>
> As I warned a few weeks ago, Jeremy has vmalloc apply_to_pte_range
> patches in mmotm, which again assault PowerPC's expectations, and
> cause lots of noise with CONFIG_PREEMPT=y CONFIG_PREEMPT_DEBUG=y.
>
> This time in vmalloc as well as vfree; and Peter's fix to the last
> lot, which went into 2.6.38, doesn't protect against these ones.
> Here's what I now see when I swapon and swapoff:
Right. And we said from day one we had the HARD WIRED assumption that
arch_enter/leave_lazy_mmu_mode() was ALWAYS going to be called within
a PTE lock section, and we did get reassurance that it was going to
remain so.
So why is it ok for them to change those and break us like that ?
Seriously, this is going out of control. If we can't even rely on
fundamental locking assumptions in the VM to remain reasonably stable
or at least get some amount of -care- from who changes them as to
whether they break others and work with us to fix them, wtf ?
I don't know what the right way to fix that is. We have an absolute
requirement that the batching we start within a lazy MMU section
is complete and flushed before any other PTE in that section can be
touched by anything else. Do we -at least- keep that guarantee ?
If yes, then maybe preempt_disable/enable() around
arch_enter/leave_lazy_mmu_mode() in apply_to_pte_range() would do...
Or maybe I should just prevent any batching of init_mm :-(
Cheers,
Ben.
next prev parent reply other threads:[~2011-03-20 23:54 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-20 4:11 mmotm threatens ppc preemption again Hugh Dickins
2011-03-20 23:53 ` Benjamin Herrenschmidt [this message]
2011-03-21 1:41 ` Hugh Dickins
2011-03-21 1:50 ` Benjamin Herrenschmidt
2011-03-21 2:20 ` Hugh Dickins
2011-03-21 2:22 ` Benjamin Herrenschmidt
2011-03-30 20:53 ` Andrew Morton
2011-03-30 21:07 ` Jeremy Fitzhardinge
2011-03-31 0:52 ` Benjamin Herrenschmidt
2011-03-31 17:21 ` Jeremy Fitzhardinge
2011-03-31 20:38 ` Benjamin Herrenschmidt
2011-05-18 23:29 ` Jeremy Fitzhardinge
2011-03-21 11:24 ` Jeremy Fitzhardinge
2011-03-21 22:52 ` Benjamin Herrenschmidt
2011-03-22 13:34 ` Jeremy Fitzhardinge
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