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Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem) causes regression for libvirt/kvm

From Christian Borntraeger <borntraeger@de.ibm.com>
Newsgroups linux.kernel
Subject Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem) causes regression for libvirt/kvm
Date 2015-09-16 09:50 +0200
Message-ID <q9fDA-6qt-19@gated-at.bofh.it> (permalink)
References (5 earlier) <q95Xz-UJ-25@gated-at.bofh.it> <q967g-18q-25@gated-at.bofh.it> <q96TE-2jT-11@gated-at.bofh.it> <q97Zn-3PQ-1@gated-at.bofh.it> <q99HP-6jL-1@gated-at.bofh.it>
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Am 16.09.2015 um 03:24 schrieb Tejun Heo:
> Hello, Paul.
> 
> On Tue, Sep 15, 2015 at 04:38:18PM -0700, Paul E. McKenney wrote:
>> Well, the decision as to what is too big for -stable is owned by the
>> -stable maintainers, not by me.
> 
> Is it tho?  Usually the subsystem maintainer knows the best and has
> most say in it.  I was mostly curious whether you'd think that the
> changes would be too risky.  If not, great.
> 
>> I am suggesting trying the options and seeing what works best, then
>> working to convince people as needed.
> 
> Yeah, sure thing.  Let's wait for Christian.

Well, I have optimized my testcase now that is puts enough pressure to
the system to  confuses system (the older 209 version, which still has
some event loop issues) that systemd restarts the journal deamon and does
several other recoveries.
To avoid regressions - even for somewhat shaky userspaces - we should
consider a revert for 4.2 stable.
There are several followup patches, which makes the revert non-trivial,
though.

The rework of the percpu rwsem seems to work fine, but we are beyond the
merge window so 4.4 seems better to me. (and consider a revert for 4.3)

Christian

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[4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Christian Borntraeger <borntraeger@de.ibm.com> - 2015-09-15 14:10 +0200
  Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Peter Zijlstra <peterz@infradead.org> - 2015-09-15 15:10 +0200
    Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Christian Borntraeger <borntraeger@de.ibm.com> - 2015-09-15 15:40 +0200
      Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Tejun Heo <tj@kernel.org> - 2015-09-15 16:00 +0200
      Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Paolo Bonzini <pbonzini@redhat.com> - 2015-09-15 18:50 +0200
        Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-09-15 19:40 +0200
          Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Paolo Bonzini <pbonzini@redhat.com> - 2015-09-16 10:40 +0200
            Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Christian Borntraeger <borntraeger@de.ibm.com> - 2015-09-16 11:00 +0200
              Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Paolo Bonzini <pbonzini@redhat.com> - 2015-09-16 11:20 +0200
                Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes  regression for libvirt/kvm Oleg Nesterov <oleg@redhat.com> - 2015-09-16 14:30 +0200
                Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Paolo Bonzini <pbonzini@redhat.com> - 2015-09-16 14:40 +0200
                Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes  regression for libvirt/kvm Oleg Nesterov <oleg@redhat.com> - 2015-09-16 14:50 +0200
                Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Christian Borntraeger <borntraeger@de.ibm.com> - 2015-09-16 15:00 +0200
                Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Tejun Heo <tj@kernel.org> - 2015-09-16 16:20 +0200
                Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Paolo Bonzini <pbonzini@redhat.com> - 2015-09-16 16:20 +0200
        Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Christian Borntraeger <borntraeger@de.ibm.com> - 2015-09-15 23:20 +0200
          Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Tejun Heo <tj@kernel.org> - 2015-09-15 23:30 +0200
            Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-09-15 23:40 +0200
              Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Tejun Heo <tj@kernel.org> - 2015-09-16 00:30 +0200
                Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-09-16 01:40 +0200
                Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Tejun Heo <tj@kernel.org> - 2015-09-16 03:30 +0200
                Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-09-16 06:40 +0200
                Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Tejun Heo <tj@kernel.org> - 2015-09-16 13:10 +0200
                Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Christian Borntraeger <borntraeger@de.ibm.com> - 2015-09-16 09:50 +0200
                Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Christian Borntraeger <borntraeger@de.ibm.com> - 2015-09-16 13:00 +0200
                Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Tejun Heo <tj@kernel.org> - 2015-09-16 13:10 +0200
                Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem) causes regression for  libvirt/kvm Christian Borntraeger <borntraeger@de.ibm.com> - 2015-09-16 14:00 +0200
  [PATCH cgroup/for-4.3-fixes 1/2] Revert "cgroup: simplify  threadgroup locking" Tejun Heo <tj@kernel.org> - 2015-09-16 18:00 +0200
    [PATCH cgroup/for-4.3-fixes 2/2] Revert "sched, cgroup: replace  signal_struct->group_rwsem with a global percpu_rwsem" Tejun Heo <tj@kernel.org> - 2015-09-16 18:00 +0200
    Re: [PATCH cgroup/for-4.3-fixes 1/2] Revert "cgroup: simplify  threadgroup locking" Oleg Nesterov <oleg@redhat.com> - 2015-09-16 19:10 +0200
    Re: [PATCH cgroup/for-4.3-fixes 1/2] Revert "cgroup: simplify  threadgroup locking" Christian Borntraeger <borntraeger@de.ibm.com> - 2015-09-16 20:50 +0200

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