dma-debug: introduce debug_dma_assert_idle()
Record actively mapped pages and provide an api for asserting a given page is dma inactive before execution proceeds. Placing debug_dma_assert_idle() in cow_user_page() flagged the violation of the dma-api in the NET_DMA implementation (see commit 77873803 "net_dma: mark broken"). The implementation includes the capability to count, in a limited way, repeat mappings of the same page that occur without an intervening unmap. This 'overlap' counter is limited to the few bits of tag space in a radix tree. This mechanism is added to mitigate false negative cases where, for example, a page is dma mapped twice and debug_dma_assert_idle() is called after the page is un-mapped once. Signed-off-by: NDan Williams <dan.j.williams@intel.com> Cc: Joerg Roedel <joro@8bytes.org> Cc: Vinod Koul <vinod.koul@intel.com> Cc: Russell King <rmk+kernel@arm.linux.org.uk> Cc: James Bottomley <JBottomley@Parallels.com> Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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