From 5848dc5b1b76d83599dcec1b39f188a7cbdca7e2 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Fri, 14 Aug 2020 15:22:43 -0700 Subject: dma-debug: remove debug_dma_assert_idle() function This remoes the code from the COW path to call debug_dma_assert_idle(), which was added many years ago. Google shows that it hasn't caught anything in the 6+ years we've had it apart from a false positive, and Hugh just noticed how it had a very unfortunate spinlock serialization in the COW path. He fixed that issue the previous commit (a85ffd59bd36: "dma-debug: fix debug_dma_assert_idle(), use rcu_read_lock()"), but let's see if anybody even notices when we remove this function entirely. NOTE! We keep the dma tracking infrastructure that was added by the commit that introduced it. Partly to make it easier to resurrect this debug code if we ever deside to, and partly because that tracking by pfn and offset looks quite reasonable. The problem with this debug code was simply that it was expensive and didn't seem worth it, not that it was wrong per se. Acked-by: Dan Williams Acked-by: Christoph Hellwig Signed-off-by: Linus Torvalds --- kernel/dma/Kconfig | 5 ----- 1 file changed, 5 deletions(-) (limited to 'kernel/dma/Kconfig') diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig index f4770fcfa62b..5732b2b3ef17 100644 --- a/kernel/dma/Kconfig +++ b/kernel/dma/Kconfig @@ -186,11 +186,6 @@ config DMA_API_DEBUG drivers like double-freeing of DMA mappings or freeing mappings that were never allocated. - This also attempts to catch cases where a page owned by DMA is - accessed by the cpu in a way that could cause data corruption. For - example, this enables cow_user_page() to check that the source page is - not undergoing DMA. - This option causes a performance degradation. Use only if you want to debug device drivers and dma interactions. -- cgit