From: Gleb Natapov <gleb@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: linux-kernel@vger.kernel.org,
Paul Gortmaker <paul.gortmaker@windriver.com>,
kvm@vger.kernel.org, jan.kiszka@siemens.com
Subject: Re: [PATCH 0/3] KVM: Make kvm_lock non-raw
Date: Sun, 22 Sep 2013 12:53:48 +0300 [thread overview]
Message-ID: <20130922095348.GJ25202@redhat.com> (raw)
In-Reply-To: <523EAFFA.6060203@redhat.com>
On Sun, Sep 22, 2013 at 10:53:14AM +0200, Paolo Bonzini wrote:
> Il 22/09/2013 09:42, Gleb Natapov ha scritto:
> > On Mon, Sep 16, 2013 at 04:06:10PM +0200, Paolo Bonzini wrote:
> >> Paul Gortmaker reported a BUG on preempt-rt kernels, due to taking the
> >> mmu_lock within the raw kvm_lock in mmu_shrink_scan. He provided a
> >> patch that shrunk the kvm_lock critical section so that the mmu_lock
> >> critical section does not nest with it, but in the end there is no reason
> >> for the vm_list to be protected by a raw spinlock. Only manipulations
> >> of kvm_usage_count and the consequent hardware_enable/disable operations
> >> are not preemptable.
> >>
> >> This small series thus splits the kvm_lock in the "raw" part and the
> >> "non-raw" part.
> >>
> >> Paul, could you please provide your Tested-by?
> >>
> > Reviewed-by: Gleb Natapov <gleb@redhat.com>
> >
> > But why should it go to stable?
>
> It is a regression from before the kvm_lock was made raw. Secondarily,
It was made raw in 2.6.39 and commit message claims that it is done for
-rt sake, why regression was noticed only now?
> it takes a much longer time before a patch hits -rt trees (can even be
> as much as a year) and this patch does nothing on non-rt trees. So
> without putting it into stable it would get no actual coverage.
>
The change is not completely trivial, it splits lock. There is no
obvious problem of course, otherwise you wouldn't send it and I
would ack it :), but it does not mean that the chance for problem is
zero, so why risk stability of stable even a little bit if the patch
does not fix anything in stable?
I do not know how -rt development goes and how it affects decisions for
stable acceptance, why can't they carry the patch in their tree until
they move to 3.12?
--
Gleb.
next prev parent reply other threads:[~2013-09-22 9:53 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-16 14:06 [PATCH 0/3] KVM: Make kvm_lock non-raw Paolo Bonzini
2013-09-16 14:06 ` [PATCH 1/3] KVM: cleanup (physical) CPU hotplug Paolo Bonzini
2013-09-17 7:57 ` Jan Kiszka
2013-09-17 23:19 ` Paolo Bonzini
2013-09-16 14:06 ` [PATCH 2/3] KVM: protect kvm_usage_count with its own spinlock Paolo Bonzini
2013-09-16 14:06 ` [PATCH 3/3] KVM: Convert kvm_lock back to non-raw spinlock Paolo Bonzini
2013-09-16 22:12 ` [PATCH 0/3] KVM: Make kvm_lock non-raw Paul Gortmaker
2013-09-20 17:51 ` Paul Gortmaker
2013-09-20 18:04 ` Jan Kiszka
2013-09-20 18:18 ` Paul Gortmaker
2013-09-20 18:27 ` Jan Kiszka
2013-09-21 20:26 ` Michael S. Tsirkin
2013-09-22 7:42 ` Gleb Natapov
2013-09-22 8:53 ` Paolo Bonzini
2013-09-22 9:53 ` Gleb Natapov [this message]
2013-09-23 6:30 ` Jan Kiszka
2013-09-23 13:36 ` Paul Gortmaker
2013-09-23 13:44 ` Paolo Bonzini
2013-09-23 14:59 ` Gleb Natapov
2013-09-23 15:05 ` Paolo Bonzini
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