linux-kernel - [tip:core/locking] lockdep: Remove cmpxchg to update nr_chain

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Message-ID: <tip-e0944ee63f7249802be74454cef81c97630ae1cd@git.kernel.org>
Date:	Fri, 22 Apr 2011 12:22:12 GMT
From:	tip-bot for Steven Rostedt <srostedt@...hat.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	torvalds@...ux-foundation.org, a.p.zijlstra@...llo.nl,
	fweisbec@...il.com, akpm@...ux-foundation.org, rostedt@...dmis.org,
	srostedt@...hat.com, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:core/locking] lockdep: Remove cmpxchg to update nr_chain_hlocks

Commit-ID:  e0944ee63f7249802be74454cef81c97630ae1cd
Gitweb:     http://git.kernel.org/tip/e0944ee63f7249802be74454cef81c97630ae1cd
Author:     Steven Rostedt <srostedt@...hat.com>
AuthorDate: Wed, 20 Apr 2011 21:42:00 -0400
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Fri, 22 Apr 2011 11:06:59 +0200

lockdep: Remove cmpxchg to update nr_chain_hlocks

For some reason nr_chain_hlocks is updated with cmpxchg, but
this is performed inside of the lockdep global "grab_lock()",
which also makes simple modification of this variable atomic.

Remove the cmpxchg logic for updating nr_chain_hlocks and
simplify the code.

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Link: http://lkml.kernel.org/r/20110421014300.727863282@goodmis.org
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/lockdep.c |   14 ++++----------
 1 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 27c609f..63437d0 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -1973,7 +1973,7 @@ static inline int lookup_chain_cache(struct task_struct *curr,
 	struct list_head *hash_head = chainhashentry(chain_key);
 	struct lock_chain *chain;
 	struct held_lock *hlock_curr, *hlock_next;
-	int i, j, n, cn;
+	int i, j;
 
 	if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
 		return 0;
@@ -2033,15 +2033,9 @@ cache_hit:
 	}
 	i++;
 	chain->depth = curr->lockdep_depth + 1 - i;
-	cn = nr_chain_hlocks;
-	while (cn + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS) {
-		n = cmpxchg(&nr_chain_hlocks, cn, cn + chain->depth);
-		if (n == cn)
-			break;
-		cn = n;
-	}
-	if (likely(cn + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {
-		chain->base = cn;
+	if (likely(nr_chain_hlocks + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {
+		chain->base = nr_chain_hlocks;
+		nr_chain_hlocks += chain->depth;
 		for (j = 0; j < chain->depth - 1; j++, i++) {
 			int lock_id = curr->held_locks[i].class_idx - 1;
 			chain_hlocks[chain->base + j] = lock_id;
--
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