linux-kernel - [PATCH 2/2] dma-debug: Put all hash-chain locks into the same lock class

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Date:	Fri, 3 Jul 2009 10:32:04 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Joerg Roedel <joerg.roedel@....com>
Subject: [PATCH 2/2] dma-debug: Put all hash-chain locks into the same lock class

From: Ingo Molnar <mingo@...e.hu>

Alan Cox reported that lockdep runs out of its stack-trace entries
with certain configs:

 BUG: MAX_STACK_TRACE_ENTRIES too low

This happens because there are 1024 hash buckets, each with a
separate lock. Lockdep puts each lock into a separate lock class and
tracks them independently.

But in reality we never take more than one of the buckets, so they
really belong into a single lock-class. Annotate the has bucket lock
init accordingly.

[ Impact: reduce the lockdep footprint of dma-debug ]

Reported-by: Alan Cox <alan@...ux.intel.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Joerg Roedel <joerg.roedel@....com>
---
 lib/dma-debug.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index a9b6b5c..c9187fe 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -716,7 +716,7 @@ void dma_debug_init(u32 num_entries)
 
 	for (i = 0; i < HASH_SIZE; ++i) {
 		INIT_LIST_HEAD(&dma_entry_hash[i].list);
-		dma_entry_hash[i].lock = SPIN_LOCK_UNLOCKED;
+		spin_lock_init(&dma_entry_hash[i].lock);
 	}
 
 	if (dma_debug_fs_init() != 0) {
-- 
1.6.3.3


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