panic in bus_dma_tag_destroy()

Matthew Dillon dillon at
Wed Oct 6 16:00:46 PDT 2004

:I'm seeing a panic in bus_dma_tag_destroy() on the free of
:dmat->segments. In comparing this to FBSD 4.10 and 5.x, the code seems
:closest to the 5.x branch with the exception that 5.x seems to defer
:the allocation of segments til bus_dmamap_create() while DFly
:allocates this in bus_dma_tag_create(). The only other thing I noticed
:was that DFly allocates segments with M_INTWAIT while FBSD allocates
:it with M_NOWAIT.

    Get a backtrace from the DDB prompt.   The 'trace' command. If you
    aren't getting a DDB prompt then compile up a kernel with 'options DDB'
    in the kernel config.

    You didn't mention which driver was faililng, but the backtrace should
    show that.  

    In anycase, if I understand your analysis the driver must be calling
    bus_dma_tag_destroy() with a NULL svd->parent_dmat.  I will analyize
    the driver and determine whether it is appropriate to have 
    bus_dma_tag_destroy() check for NULL or whether it is appropriate for
    the driver to check for NULL and not call bus_dma_tag_destroy().

					Matthew Dillon 
					<dillon at xxxxxxxxxxxxx>

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