Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Mon, 8 May 2017 11:19:44 +0200 | Subject | Re: [PATCH 0/2] Fix incorrect warning from dma-debug |
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Hi Jon,
On Sun, May 7, 2017 at 2:06 AM, Jon Masters <jcm@jonmasters.org> wrote: > On 05/09/2016 06:00 AM, Robin Murphy wrote: >> On 09/05/16 10:37, Robin Murphy wrote: >>> On 08/05/16 11:59, Niklas Söderlund wrote: >>>> While using CONFIG_DMA_API_DEBUG i came across this warning which I >>>> think is a false positive. As shown dma_sync_single_for_device() are >>>> called from the dma_map_single() call path. This triggers the warning >>>> since the dma-debug code have not yet been made aware of the mapping. >>> >>> Almost right ;) The thing being mapped (the SPI device's buffer) and the >>> thing being synced (the IOMMU's PTE) are entirely unrelated. Due to the >>> current of_iommu_init() setup, the IOMMU is probed long before >>> dma_debug_init() gets called, therefore DMA debug is missing entries for >>> some of the initial page table mappings and gets confused when we update >>> them later. > > What was the eventual followup/fix for this? We're seeing similar traces > to this during internal testing of 4.11 kernels.
A quick hack is to change arch/arm64/mm/dma-mapping.c:dma_debug_do_init() from fs_initcall() to arch_initcall().
However, then you loose the debugfs features. A proper fix would involve splitting dma_debug_init() in two phases: an early one doing the real work, and a late one registering the debugfs interface.
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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