Re: [GIT PULL rcu/urgent-for-mingo] Regression fixes

[Ingo Molnar <mingo@kernel.org>]

* Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:

> Hello, Ingo,
> 
> This pull request contains a couple of fixes for RCU regressions:
> 
> 1.	Complete the work of commit dd56af42bd82 (rcu: Eliminate deadlock
> 	between CPU hotplug and expedited grace periods), which was
> 	intended to allow synchronize_sched_expedited() to be safely
> 	used when holding locks acquired by CPU-hotplug notifiers.
> 	This commit makes the put_online_cpus() avoid the deadlock
> 	instead of just handling the get_online_cpus().
> 
> 2.	Complete the work of commit 35ce7f29a44a (rcu: Create rcuo
> 	kthreads only for onlined CPUs), which was intended to allow
> 	RCU to avoid allocating unneeded kthreads on systems where the
> 	firmware says that there are more CPUs than are really present.
> 	This commit makes rcu_barrier() aware of the mismatch, so that
> 	it doesn't hang waiting for non-existent CPUs.  (And yes, I do
> 	need to force this non-existent-CPU condition into my testing.)
> 
> Both of these changes have been tested by the submitters and have been
> exposed to -next testing.  These changes are needed to avoid system hangs,
> and these system hangs have actually occurred during mainline testing.
> 
> These changes are available in the git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git urgent-for-mingo
> 
> for you to fetch changes up to d7e29933969e5ca7c112ce1368a07911f4485dc2:
> 
>   rcu: Make rcu_barrier() understand about missing rcuo kthreads (2014-10-28 13:24:13 -0700)
> 
> ----------------------------------------------------------------
> Paul E. McKenney (2):
>       rcu: More on deadlock between CPU hotplug and expedited grace periods
>       rcu: Make rcu_barrier() understand about missing rcuo kthreads
> 
>  include/trace/events/rcu.h | 18 +++++++++---------
>  kernel/cpu.c               | 14 +++++++++++++-
>  kernel/rcu/tree.c          | 15 ++++++++++-----
>  kernel/rcu/tree.h          |  1 +
>  kernel/rcu/tree_plugin.h   | 33 +++++++++++++++++++++++++++++++++
>  5 files changed, 66 insertions(+), 15 deletions(-)
> 

Pulled, thanks a lot Paul!

	Ingo