linux-kernel - [PATCH] lockdep: fix mismatched lockdep_depth/curr_chain

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Date:	Fri, 05 Oct 2007 11:31:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Gregory Haskins <ghaskins@...ell.com>, stable <stable@...nel.org>
Cc:	mingo@...e.hu, linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] lockdep: fix mismatched lockdep_depth/curr_chain_hash


Stable team,

please consider this patch for the next 22-stable.

---
Subject: lockdep: fix mismatched lockdep_depth/curr_chain_hash
From: Gregory Haskins <ghaskins@...ell.com>

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>
---
 kernel/lockdep.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/kernel/lockdep.c
===================================================================
--- linux-2.6.orig/kernel/lockdep.c
+++ linux-2.6/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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