linux-kernel - Re: [PATCH 0/3] dma-debug: add additional checks

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Message-ID: <20090318121940.GT6159@amd.com>
Date:	Wed, 18 Mar 2009 13:19:40 +0100
From:	Joerg Roedel <joerg.roedel@....com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Ingo Molnar <mingo@...e.hu>, Ingo Molnar <mingo@...hat.com>,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] dma-debug: add additional checks

On Wed, Mar 18, 2009 at 12:38:47PM +0100, Peter Zijlstra wrote:
> On Wed, 2009-03-18 at 12:23 +0100, Ingo Molnar wrote:
> > another -tip testbox started triggering:
> > 
> >   BUG: MAX_LOCKDEP_ENTRIES too low!
> > 
> > it triggers due to CONFIG_DMA_API_DEBUG=y. Config attached.
> 
> 
> I still have this laying about.. could be we're just at the limit due to
> lock bloat in the kernel, could be dma_api_debug is doing something
> all-together iffy

I had a look and the maximum locking depth in dma-debug code was two.
Attached patch reduces this to one.

>From d28fc4a308bf66ed98c68e1db18e4e1434206541 Mon Sep 17 00:00:00 2001
From: Joerg Roedel <joerg.roedel@....com>
Date: Wed, 18 Mar 2009 13:15:20 +0100
Subject: [PATCH] dma-debug: serialize locking in unmap path

Impact: reduce maximum lockdepth to one

This patch reduces the maximum spin lock depth from two to one in the
dma-debug code.

Signed-off-by: Joerg Roedel <joerg.roedel@....com>
---
 lib/dma-debug.c |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index 9a350b4..3bd8d1d 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -542,7 +542,8 @@ static void check_unmap(struct dma_debug_entry *ref)
 			   "to free DMA memory it has not allocated "
 			   "[device address=0x%016llx] [size=%llu bytes]\n",
 			   ref->dev_addr, ref->size);
-		goto out;
+		put_hash_bucket(bucket, &flags);
+		return;
 	}
 
 	if (ref->size != entry->size) {
@@ -593,10 +594,8 @@ static void check_unmap(struct dma_debug_entry *ref)
 	}
 
 	hash_bucket_del(entry);
-	dma_entry_free(entry);
-
-out:
 	put_hash_bucket(bucket, &flags);
+	dma_entry_free(entry);
 }
 
 static void check_for_stack(struct device *dev, void *addr)
-- 
1.5.6.4


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