On Sun, Sep 16, 2012 at 06:52:51PM -0600, Shuah Khan wrote: > A recent dma mapping error analysis effort showed that a large percentage > of dma_map_single() and dma_map_page() returns are not checked for mapping > errors. > > Reference: > http://linuxdriverproject.org/mediawiki/index.php/DMA_Mapping_Error_Analysis > > Adding support for tracking dma mapping and unmapping errors to help assess > the following: > > When do dma mapping errors get detected? > How often do these errors occur? > Why don't we see failures related to missing dma mapping error checks? > Are they silent failures? > > Four new fields are added to struct device when CONFIG_DMA_API_DEBUG is > enabled, to track the following: > > dma_map_errors: > Total number of dma mapping errors returned by the dma mapping interfaces, > in response to mapping requests from this device. > dma_map_errors_not_checked: > Total number of dma mapping errors the device failed to check before using > the returned address. > dma_unmap_errors: > Total number of times the device tried to unmap or free an invalid dma > address. > iotlb_overflow_cnt: > Tracks how many times a swiotlb overflow buffer is returned to this device > when regular iotlb is full. > > Enhancements to dma-debug api are made to add new debugfs interfaces to > report total dma errors, dma errors that are not checked, and unmap errors > for the entire system. Please note that these are counts for all devices in > the system. > > The following new dma-debug interfaces are added: > > debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr): > Tracks dma mapping errors checked by the device. It decrements > the dma_map_errors_not_checked counter that was incremented by > debug_dma_map_page() when it checked for errors. > debug_dma_dump_map_errors(struct device *dev, int all): > Allows dump of dma mapping error summary or just the errors if any. > > The following existing dma-debug api are changed to support this feature: > debug_dma_map_page(): > Increments dma_map_errors and dma_map_errors_not_checked errors for > the current device as well as totals for the system, dma-debug api > keeps track of, when dma_addr is invalid. Please note that this > routine can no longer call dma_mapping_error(), because of the newly > added debug_dma_mapping_error() interface. Calling this routine at the > time dma error unchecked state is registered, will not help if state > gets changed right away. > check_unmap(): > This is an existing internal routines that checks for unmap errors, > changed to increment dma_unmap_errors for the current device, as well > as the dma_unmap_errors counter for the system, dma-debug api keeps > track of, when a device requests an invalid address to be unmapped. > Please note that this routine can no longer call dma_mapping_error(), > because of the newly added debug_dma_mapping_error() interface. Calling > dma_mapping_error() from this routine will decrement > dma_map_errors_not_checked counter incorrectly. I like the direction of this patch. That said I am wondering why you choose to do it this way? Was there no way to have all of the logic within debug dma file, and within check_unmap? > > The following new swiotlb interface is changed: > swiotlb_map_page(): > Increments iotlb_overflow_cnt for the device when iotlb overflow > buffer is returned when swiotlb is full. > > Changed arch/x86/include/asm/dma-mapping.h to call debug_dma_mapping_error() > to validate these new interfaces on x86_64. Other architectures will be > changed in a subsequent patch. > > The current dma-debug infrastructure is designed to track dma mappings, and > debug entries are added only for correctly mapped addresses and not when > mapping fails. Enhancing the current infrastructure to track failed mappings > will result in unnecessary complexity. The approach to add counters to What is the extra complexity? Can you explain as if I was a newbie to debug DMA API - perhaps there is still some hope in doing it there? > struct device eliminates the need for maintaining failed mappings in dma-debug > infrastructure and is cleaner and simpler without impacting the existing > dma-debug infrastructure. Could you explain please why it would be more difficult to do it in the existing dma-debug infrastructure? -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
