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SubjectRe: Hang: 2.6.32.4 sky2/DMAR (was [PATCH] sky2: Fix WARNING: at lib/dma-debug.c:902 check_sync)
On Thu, 28 Jan 2010 11:43:16 -0500
Michael Breuer <mbreuer@majjas.com> wrote:

> Update: I played with dma-debug. Was being disabled due to lack of
> memory. I forced it back on while pumping traffic through and got this:
> Jan 28 11:39:30 mail kernel: ------------[ cut here ]------------
> Jan 28 11:39:30 mail kernel: WARNING: at lib/dma-debug.c:902
> check_sync+0xc1/0x43f()
> Jan 28 11:39:30 mail kernel: Hardware name: System Product Name
> Jan 28 11:39:30 mail kernel: sky2 0000:06:00.0: DMA-API: device driver
> tries to sync DMA memory it has not allocated [device

This test in dma-debug is bogus. Because the debug code matches
dma based on address and size; and is perfectly valid to sync a value
less than size. This is the patch I sent earlier, it isn't 100%
correct but it will let you keep testing
....................................

This should fix the dma-debug API code (and documentation), to
avoid false positives when sync is done on a partial map.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>

--- a/Documentation/DMA-API.txt 2010-01-20 15:17:01.390143729 -0800
+++ b/Documentation/DMA-API.txt 2010-01-20 15:18:48.967875255 -0800
@@ -377,9 +377,10 @@ void
pci_dma_sync_sg(struct pci_dev *hwdev, struct scatterlist *sg,
int nelems, int direction)

-Synchronise a single contiguous or scatter/gather mapping. All the
-parameters must be the same as those passed into the single mapping
-API.
+Synchronise a single contiguous or scatter/gather mapping. The
+device and handle must be the same as those passed into the single mapping
+API. The size can be less than the original mapping if only part
+of the mapping needs to be accessed.

Notes: You must do this:

--- a/lib/dma-debug.c 2010-01-20 15:22:55.919519883 -0800
+++ b/lib/dma-debug.c 2010-01-20 15:26:31.648895638 -0800
@@ -285,11 +285,9 @@ static struct dma_debug_entry *hash_buck
}

/*
- * If we have multiple matches but no perfect-fit, just return
- * NULL.
+ * If we have multiple matches but no perfect-fit
+ * return best value and let caller deal with it.
*/
- ret = (matches == 1) ? ret : NULL;
-
return ret;
}


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