linux-kernel - [PATCH 1/2] dma-debug: Fix locking bug in check

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Message-ID: <20130318221243.7349.64147.stgit@ahduyck-cp1.jf.intel.com>
Date:	Mon, 18 Mar 2013 15:12:43 -0700
From:	Alexander Duyck <alexander.h.duyck@...el.com>
To:	linux-kernel@...r.kernel.org
Cc:	konrad.wilk@...cle.com, joerg.roedel@....com, konrad@...nel.org,
	christoph.paasch@...ouvain.be, mingo@...hat.com,
	shuahkhan@...il.com, hpa@...or.com, akpm@...ux-foundation.org,
	shuah.khan@...com, netdev@...r.kernel.org,
	jeffrey.t.kirsher@...el.com
Subject: [PATCH 1/2] dma-debug: Fix locking bug in check_unmap

In check_unmap it is possible to get into a dead-locked state if
dma_mapping_error is called.  The problem is that the bucket is locked in
check_unmap, and locked again by debug_dma_mapping_error which is called by
dma_mapping_error.  To resolve that we must release the lock on the bucket
before making the call to dma_mapping_error.

Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
---
 lib/dma-debug.c |   18 +++++++++---------
 1 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index 5e396ac..724bd4d 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -862,17 +862,18 @@ static void check_unmap(struct dma_debug_entry *ref)
 	entry = bucket_find_exact(bucket, ref);
 
 	if (!entry) {
+		/* must drop lock before calling dma_mapping_error */
+		put_hash_bucket(bucket, &flags);
+
 		if (dma_mapping_error(ref->dev, ref->dev_addr)) {
 			err_printk(ref->dev, NULL,
-				   "DMA-API: device driver tries "
-				   "to free an invalid DMA memory address\n");
-			return;
+				   "DMA-API: device driver tries to free an invalid DMA memory address\n");
+		} else {
+			err_printk(ref->dev, NULL,
+				   "DMA-API: device driver tries to free DMA memory it has not allocated [device address=0x%016llx] [size=%llu bytes]\n",
+				   ref->dev_addr, ref->size);
 		}
-		err_printk(ref->dev, NULL, "DMA-API: device driver tries "
-			   "to free DMA memory it has not allocated "
-			   "[device address=0x%016llx] [size=%llu bytes]\n",
-			   ref->dev_addr, ref->size);
-		goto out;
+		return;
 	}
 
 	if (ref->size != entry->size) {
@@ -936,7 +937,6 @@ static void check_unmap(struct dma_debug_entry *ref)
 	hash_bucket_del(entry);
 	dma_entry_free(entry);
 
-out:
 	put_hash_bucket(bucket, &flags);
 }
 

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