From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Date: Fri, 6 Jul 2012 12:59:20 +0000 (-0700)
Subject: Merge branches 'bigrtm.2012.07.04a', 'doctorture.2012.07.02a', 'fixes.2012.07.06a... 
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=02a0677b0be545a07ffb15a13419efd7c82881e0;p=linux-beck.git

Merge branches 'bigrtm.2012.07.04a', 'doctorture.2012.07.02a', 'fixes.2012.07.06a' and 'fnh.2012.07.02a' into HEAD

bigrtm: First steps towards getting RCU out of the way of
	tens-of-microseconds real-time response on systems compiled
	with NR_CPUS=4096.  Also cleanups for and increased concurrency
	of rcu_barrier() family of primitives.
doctorture: rcutorture and documentation improvements.
fixes:  Miscellaneous fixes.
fnh: RCU_FAST_NO_HZ fixes and improvements.
---

02a0677b0be545a07ffb15a13419efd7c82881e0
diff --cc kernel/rcutree.c
index 967b4bed2cf3,4b97bba7396e,4154c9567a6d,6eb48f13eeeb..117218a43724
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@@@@ -2316,46 -2295,14 -2306,14 -2295,14 +2327,46 @@@@@ static void _rcu_barrier(struct rcu_sta
    	int cpu;
    	unsigned long flags;
    	struct rcu_data *rdp;
 ---	struct rcu_head rh;
 +++	struct rcu_data rd;
 +++	unsigned long snap = ACCESS_ONCE(rsp->n_barrier_done);
 +++	unsigned long snap_done;
    
 ---	init_rcu_head_on_stack(&rh);
 +++	init_rcu_head_on_stack(&rd.barrier_head);
 +++	_rcu_barrier_trace(rsp, "Begin", -1, snap);
    
    	/* Take mutex to serialize concurrent rcu_barrier() requests. */
 ---	mutex_lock(&rcu_barrier_mutex);
 +++	mutex_lock(&rsp->barrier_mutex);
 + +
  - 	smp_mb();  /* Prevent any prior operations from leaking in. */
 +++	/*
 +++	 * Ensure that all prior references, including to ->n_barrier_done,
 +++	 * are ordered before the _rcu_barrier() machinery.
 +++	 */
 +++	smp_mb();  /* See above block comment. */
 +++
 +++	/*
 +++	 * Recheck ->n_barrier_done to see if others did our work for us.
 +++	 * This means checking ->n_barrier_done for an even-to-odd-to-even
 +++	 * transition.  The "if" expression below therefore rounds the old
 +++	 * value up to the next even number and adds two before comparing.
 +++	 */
 +++	snap_done = ACCESS_ONCE(rsp->n_barrier_done);
 +++	_rcu_barrier_trace(rsp, "Check", -1, snap_done);
 +++	if (ULONG_CMP_GE(snap_done, ((snap + 1) & ~0x1) + 2)) {
 +++		_rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
 +++		smp_mb(); /* caller's subsequent code after above check. */
 +++		mutex_unlock(&rsp->barrier_mutex);
 +++		return;
 +++	}
  + 
 - -	smp_mb();  /* Prevent any prior operations from leaking in. */
 +++	/*
 +++	 * Increment ->n_barrier_done to avoid duplicate work.  Use
 +++	 * ACCESS_ONCE() to prevent the compiler from speculating
 +++	 * the increment to precede the early-exit check.
 +++	 */
 +++	ACCESS_ONCE(rsp->n_barrier_done)++;
 +++	WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1);
 +++	_rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done);
 +++	smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
    
    	/*
    	 * Initialize the count to one rather than to zero in order to