Pull more locking changes from Ingo Molnar:
 "This is the second round of locking tree updates for v3.16, offering
  large system scalability improvements:

 - optimistic spinning for rwsems, from Davidlohr Bueso.

 - 'qrwlocks' core code and x86 enablement, from Waiman Long and PeterZ"

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86, locking/rwlocks: Enable qrwlocks on x86
  locking/rwlocks: Introduce 'qrwlocks' - fair, queued rwlocks
  locking/mutexes: Documentation update/rewrite
  locking/rwsem: Fix checkpatch.pl warnings
  locking/rwsem: Fix warnings for CONFIG_RWSEM_GENERIC_SPINLOCK
  locking/rwsem: Support optimistic spinning

This rwlock uses the arch_spin_lock_t as a waitqueue, and assuming the
arch_spin_lock_t is a fair lock (ticket,mcs etc..) the resulting
rwlock is a fair lock.

It fits in the same 8 bytes as the regular rwlock_t by folding the
reader and writer count into a single integer, using the remaining 4
bytes for the arch_spinlock_t.

Architectures that can single-copy adress bytes can optimize
queue_write_unlock() with a 0 write to the LSB (the write count).

Performance as measured by Davidlohr Bueso (rwlock_t -> qrwlock_t):

 +--------------+-------------+---------------+
 |   Workload   |   #users    |     delta     |
 +--------------+-------------+---------------+
 | alltests     | > 1400      | -4.83%        |
 | custom       | 0-100,> 100 | +1.43%,-1.57% |
 | high_systime | > 1000      | -2.61         |
 | shared       | all         | +0.32         |
 +--------------+-------------+---------------+

http://www.stgolabs.net/qrwlock-stuff/aim7-results-vs-rwsem_optsin/

Signed-off-by: Waiman Long <Waiman.Long@hp.com>
[peterz: near complete rewrite]
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Paul E.McKenney" <paulmck@linux.vnet.ibm.com>
Cc: linux-arch@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/n/tip-gac1nnl3wvs2ij87zv2xkdzq@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

WARNING: line over 80 characters
#205: FILE: kernel/locking/rwsem-xadd.c:275:
+		old = cmpxchg(&sem->count, count, count + RWSEM_ACTIVE_WRITE_BIAS);

WARNING: line over 80 characters
#376: FILE: kernel/locking/rwsem-xadd.c:434:
+		 * If there were already threads queued before us and there are no

WARNING: line over 80 characters
#377: FILE: kernel/locking/rwsem-xadd.c:435:
+		 * active writers, the lock must be read owned; so we try to wake

total: 0 errors, 3 warnings, 417 lines checked

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Davidlohr Bueso <davidlohr@hp.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-pn6pslaplw031lykweojsn8c@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

We have reached the point where our mutexes are quite fine tuned
for a number of situations. This includes the use of heuristics
and optimistic spinning, based on MCS locking techniques.

Exclusive ownership of read-write semaphores are, conceptually,
just about the same as mutexes, making them close cousins. To
this end we need to make them both perform similarly, and
right now, rwsems are simply not up to it. This was discovered
by both reverting commit 4fc3f1d6 (mm/rmap, migration: Make
rmap_walk_anon() and try_to_unmap_anon() more scalable) and
similarly, converting some other mutexes (ie: i_mmap_mutex) to
rwsems. This creates a situation where users have to choose
between a rwsem and mutex taking into account this important
performance difference. Specifically, biggest difference between
both locks is when we fail to acquire a mutex in the fastpath,
optimistic spinning comes in to play and we can avoid a large
amount of unnecessary sleeping and overhead of moving tasks in
and out of wait queue. Rwsems do not have such logic.

This patch, based on the work from Tim Chen and I, adds support
for write-side optimistic spinning when the lock is contended.
It also includes support for the recently added cancelable MCS
locking for adaptive spinning. Note that is is only applicable
to the xadd method, and the spinlock rwsem variant remains intact.

Allowing optimistic spinning before putting the writer on the wait
queue reduces wait queue contention and provided greater chance
for the rwsem to get acquired. With these changes, rwsem is on par
with mutex. The performance benefits can be seen on a number of
workloads. For instance, on a 8 socket, 80 core 64bit Westmere box,
aim7 shows the following improvements in throughput:

 +--------------+---------------------+-----------------+
 |   Workload   | throughput-increase | number of users |
 +--------------+---------------------+-----------------+
 | alltests     | 20%                 | >1000           |
 | custom       | 27%, 60%            | 10-100, >1000   |
 | high_systime | 36%, 30%            | >100, >1000     |
 | shared       | 58%, 29%            | 10-100, >1000   |
 +--------------+---------------------+-----------------+

There was also improvement on smaller systems, such as a quad-core
x86-64 laptop running a 30Gb PostgreSQL (pgbench) workload for up
to +60% in throughput for over 50 clients. Additionally, benefits
were also noticed in exim (mail server) workloads. Furthermore, no
performance regression have been seen at all.

Based-on-work-from: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
[peterz: rej fixup due to comment patches, sched/rt.h header]
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Alex Shi <alex.shi@linaro.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: "Paul E.McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Scott J Norton" <scott.norton@hp.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <jbacik@fusionio.com>
Link: http://lkml.kernel.org/r/1399055055.6275.15.camel@buesod1.americas.hpqcorp.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

Pull scheduler updates from Ingo Molnar:
 "The main scheduling related changes in this cycle were:

   - various sched/numa updates, for better performance

   - tree wide cleanup of open coded nice levels

   - nohz fix related to rq->nr_running use

   - cpuidle changes and continued consolidation to improve the
     kernel/sched/idle.c high level idle scheduling logic.  As part of
     this effort I pulled cpuidle driver changes from Rafael as well.

   - standardized idle polling amongst architectures

   - continued work on preparing better power/energy aware scheduling

   - sched/rt updates

   - misc fixlets and cleanups"

* 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (49 commits)
  sched/numa: Decay ->wakee_flips instead of zeroing
  sched/numa: Update migrate_improves/degrades_locality()
  sched/numa: Allow task switch if load imbalance improves
  sched/rt: Fix 'struct sched_dl_entity' and dl_task_time() comments, to match the current upstream code
  sched: Consolidate open coded implementations of nice level frobbing into nice_to_rlimit() and rlimit_to_nice()
  sched: Initialize rq->age_stamp on processor start
  sched, nohz: Change rq->nr_running to always use wrappers
  sched: Fix the rq->next_balance logic in rebalance_domains() and idle_balance()
  sched: Use clamp() and clamp_val() to make sys_nice() more readable
  sched: Do not zero sg->cpumask and sg->sgp->power in build_sched_groups()
  sched/numa: Fix initialization of sched_domain_topology for NUMA
  sched: Call select_idle_sibling() when not affine_sd
  sched: Simplify return logic in sched_read_attr()
  sched: Simplify return logic in sched_copy_attr()
  sched: Fix exec_start/task_hot on migrated tasks
  arm64: Remove TIF_POLLING_NRFLAG
  metag: Remove TIF_POLLING_NRFLAG
  sched/idle: Make cpuidle_idle_call() void
  sched/idle: Reflow cpuidle_idle_call()
  sched/idle: Delay clearing the polling bit
  ...

Pull core locking updates from Ingo Molnar:
 "The main changes in this cycle were:

   - reduced/streamlined smp_mb__*() interface that allows more usecases
     and makes the existing ones less buggy, especially in rarer
     architectures

   - add rwsem implementation comments

   - bump up lockdep limits"

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (33 commits)
  rwsem: Add comments to explain the meaning of the rwsem's count field
  lockdep: Increase static allocations
  arch: Mass conversion of smp_mb__*()
  arch,doc: Convert smp_mb__*()
  arch,xtensa: Convert smp_mb__*()
  arch,x86: Convert smp_mb__*()
  arch,tile: Convert smp_mb__*()
  arch,sparc: Convert smp_mb__*()
  arch,sh: Convert smp_mb__*()
  arch,score: Convert smp_mb__*()
  arch,s390: Convert smp_mb__*()
  arch,powerpc: Convert smp_mb__*()
  arch,parisc: Convert smp_mb__*()
  arch,openrisc: Convert smp_mb__*()
  arch,mn10300: Convert smp_mb__*()
  arch,mips: Convert smp_mb__*()
  arch,metag: Convert smp_mb__*()
  arch,m68k: Convert smp_mb__*()
  arch,m32r: Convert smp_mb__*()
  arch,ia64: Convert smp_mb__*()
  ...

Pull RCU changes from Ingo Molnar:
 "The main RCU changes in this cycle were:

   - RCU torture-test changes.

   - variable-name renaming cleanup.

   - update RCU documentation.

   - miscellaneous fixes.

   - patch to suppress RCU stall warnings while sysrq requests are being
     processed"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (68 commits)
  rcu: Provide API to suppress stall warnings while sysrc runs
  rcu: Variable name changed in tree_plugin.h and used in tree.c
  torture: Remove unused definition
  torture: Remove __init from torture_init_begin/end
  torture: Check for multiple concurrent torture tests
  locktorture: Remove reference to nonexistent Kconfig parameter
  rcutorture: Run rcu_torture_writer at normal priority
  rcutorture: Note diffs from git commits
  rcutorture: Add missing destroy_timer_on_stack()
  rcutorture: Explicitly test synchronous grace-period primitives
  rcutorture:  Add tests for get_state_synchronize_rcu()
  rcutorture: Test RCU-sched primitives in TREE_PREEMPT_RCU kernels
  torture: Use elapsed time to detect hangs
  rcutorture: Check for rcu_torture_fqs creation errors
  torture: Better summary diagnostics for build failures
  torture: Notice if an all-zero cpumask is passed inside a critical section
  rcutorture: Make rcu_torture_reader() use cond_resched()
  sched,rcu: Make cond_resched() report RCU quiescent states
  percpu: Fix raw_cpu_inc_return()
  rcutorture: Export RCU grace-period kthread wait state to rcutorture
  ...

The current deadlock detection logic does not work reliably due to the
following early exit path:

	/*
	 * Drop out, when the task has no waiters. Note,
	 * top_waiter can be NULL, when we are in the deboosting
	 * mode!
	 */
	if (top_waiter && (!task_has_pi_waiters(task) ||
			   top_waiter != task_top_pi_waiter(task)))
		goto out_unlock_pi;

So this not only exits when the task has no waiters, it also exits
unconditionally when the current waiter is not the top priority waiter
of the task.

So in a nested locking scenario, it might abort the lock chain walk
and therefor miss a potential deadlock.

Simple fix: Continue the chain walk, when deadlock detection is
enabled.

We also avoid the whole enqueue, if we detect the deadlock right away
(A-A). It's an optimization, but also prevents that another waiter who
comes in after the detection and before the task has undone the damage
observes the situation and detects the deadlock and returns
-EDEADLOCK, which is wrong as the other task is not in a deadlock
situation.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20140522031949.725272460@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Pull RCU updates from Paul E. McKenney:

" 1.      Update RCU documentation.  These were posted to LKML at
          https://lkml.org/lkml/2014/4/28/634.

  2.      Miscellaneous fixes.  These were posted to LKML at
          https://lkml.org/lkml/2014/4/28/645.

  3.      Torture-test changes.  These were posted to LKML at
          https://lkml.org/lkml/2014/4/28/667.

  4.      Variable-name renaming cleanup, sent separately due to conflicts.
          This was posted to LKML at https://lkml.org/lkml/2014/5/13/854.

  5.      Patch to suppress RCU stall warnings while sysrq requests are
          being processed.  This patch is the RCU portions of the patch
          that Rik posted to LKML at https://lkml.org/lkml/2014/4/29/457.
          The reason for pushing this patch ahead instead of waiting until
          3.17 is that the NMI-based stack traces are messing up sysrq
          output, and in some cases also messing up the system as well."

Signed-off-by: Ingo Molnar <mingo@kernel.org>

Signed-off-by: Ingo Molnar <mingo@kernel.org>