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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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