linux-kernel - [patch 27/26] lockdep: fix mismatched lockdep_depth/curr_chain_hash

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Date:	Wed, 31 Oct 2007 09:25:14 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org,
	Justin Forbes <jmforbes@...uxtx.org>,
	Zwane Mwaikambo <zwane@....linux.org.uk>,
	Theodore Ts'o <tytso@....edu>,
	Randy Dunlap <rdunlap@...otime.net>,
	Dave Jones <davej@...hat.com>,
	Chuck Wolber <chuckw@...ntumlinux.com>,
	Chris Wedgwood <reviews@...cw.f00f.org>,
	Michael Krufky <mkrufky@...uxtv.org>,
	Chuck Ebbert <cebbert@...hat.com>,
	Domenico Andreoli <cavokz@...il.com>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk
Subject: [patch 27/26] lockdep: fix mismatched lockdep_depth/curr_chain_hash

[one more patch added to the 2.6.22-stable queue]


From: Gregory Haskins <ghaskins@...ell.com>

patch 3aa416b07f0adf01c090baab26fb70c35ec17623 in mainline.

lockdep: fix mismatched lockdep_depth/curr_chain_hash

It is possible for the current->curr_chain_key to become inconsistent with the
current index if the chain fails to validate.  The end result is that future
lock_acquire() operations may inadvertently fail to find a hit in the cache
resulting in a new node being added to the graph for every acquire.

[ peterz: this might explain some of the lockdep is so _slow_ complaints. ]
[ mingo: this does not impact the correctness of validation, but may slow
  down future operations significantly, if the chain gets very long. ]

Signed-off-by: Gregory Haskins <ghaskins@...ell.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -2166,7 +2166,6 @@ out_calc_hash:
 	}
 #endif
 	chain_key = iterate_chain_key(chain_key, id);
-	curr->curr_chain_key = chain_key;
 
 	/*
 	 * Trylock needs to maintain the stack of held locks, but it
@@ -2215,6 +2214,7 @@ out_calc_hash:
 		if (unlikely(!debug_locks))
 			return 0;
 
+	curr->curr_chain_key = chain_key;
 	curr->lockdep_depth++;
 	check_chain_key(curr);
 #ifdef CONFIG_DEBUG_LOCKDEP

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