Messages in this thread | | | Subject | Re: kernel BUG at mm/huge_memory.c:2613! | From | Robin Murphy <> | Date | Mon, 22 Jun 2020 16:30:41 +0100 |
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On 2020-06-22 13:46, Joerg Roedel wrote: > + Robin > > Robin, any idea on this?
After a bit of archaeology, this dates back to the original review:
https://lore.kernel.org/linux-arm-kernel/54C285D4.3070802@arm.com/ https://lore.kernel.org/linux-arm-kernel/54DA2666.9030003@arm.com/
In summary: originally this inherited from other arch code that did simply strip __GFP_COMP; that was deemed questionable because of the nonsensical comment about CONFIG_HUGETLBFS that was stuck to it; the current code is like it is because in 5 and a half years nobody said that it's wrong :)
If there actually *are* good reasons for stripping __GFP_COMP, then I've certainly no objection to doing so.
Robin.
> On Thu, Jun 18, 2020 at 10:40:26PM -0400, Andrea Arcangeli wrote: >> Hello, >> >> On Thu, Jun 18, 2020 at 06:14:49PM -0700, Roman Gushchin wrote: >>> I agree. The whole >>> >>> page = alloc_pages_node(nid, alloc_flags, order); >>> if (!page) >>> continue; >>> if (!order) >>> break; >>> if (!PageCompound(page)) { >>> split_page(page, order); >>> break; >>> } else if (!split_huge_page(page)) { >>> break; >>> } >>> >>> looks very suspicious to me. >>> My wild guess is that gfp flags changed somewhere above, so we hit >>> the branch which was never hit before. >> >> Right to be suspicious about the above: split_huge_page on a regular >> page allocated by a driver was never meant to work. >> >> The PageLocked BUG_ON is just a symptom of a bigger issue, basically >> split_huge_page it may survive, but it'll stay compound and in turn it >> must be freed as compound. >> >> The respective free method doesn't even contemplate freeing compound >> pages, the only way the free method can survive, is by removing >> __GFP_COMP forcefully in the allocation that was perhaps set here >> (there are that many __GFP_COMP in that directory): >> >> static void snd_malloc_dev_pages(struct snd_dma_buffer *dmab, size_t size) >> { >> gfp_t gfp_flags; >> >> gfp_flags = GFP_KERNEL >> | __GFP_COMP /* compound page lets parts be mapped */ >> >> And I'm not sure what the comment means here, compound or non compound >> doesn't make a difference when you map it, it's not a THP, the >> mappings must be handled manually so nothing should check PG_compound >> anyway in the mapping code. >> >> Something like this may improve things, it's an untested quick hack, >> but this assumes it's always a bug to setup a compound page for these >> DMA allocations and given the API it's probably a correct >> assumption.. Compound is slower, unless you need it, you can avoid it >> and then split_page will give contiguous memory page granular. Ideally >> the code shouldn't call split_page at all and it should free it all at >> once by keeping track of the order and by returning the order to the >> caller, something the API can't do right now as it returns a plain >> array that can only represent individual small pages. >> >> Once this is resolved, you may want to check your config, iommu passthrough >> sounds more optimal for a soundcard. >> >> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c >> index f68a62c3c32b..3dfbc010fa83 100644 >> --- a/drivers/iommu/dma-iommu.c >> +++ b/drivers/iommu/dma-iommu.c >> @@ -499,6 +499,10 @@ static struct page **__iommu_dma_alloc_pages(struct device *dev, >> >> /* IOMMU can map any pages, so himem can also be used here */ >> gfp |= __GFP_NOWARN | __GFP_HIGHMEM; >> + if (unlikely(gfp & __GFP_COMP)) { >> + WARN(); >> + gfp &= ~__GFP_COMP; >> + } >> >> while (count) { >> struct page *page = NULL; >> @@ -522,13 +526,8 @@ static struct page **__iommu_dma_alloc_pages(struct device *dev, >> continue; >> if (!order) >> break; >> - if (!PageCompound(page)) { >> - split_page(page, order); >> - break; >> - } else if (!split_huge_page(page)) { >> - break; >> - } >> - __free_pages(page, order); >> + split_page(page, order); >> + break; >> } >> if (!page) { >> __iommu_dma_free_pages(pages, i); >> diff --git a/sound/core/memalloc.c b/sound/core/memalloc.c >> index 6850d13aa98c..378f5a36ec5f 100644 >> --- a/sound/core/memalloc.c >> +++ b/sound/core/memalloc.c >> @@ -28,7 +28,6 @@ static void snd_malloc_dev_pages(struct snd_dma_buffer *dmab, size_t size) >> gfp_t gfp_flags; >> >> gfp_flags = GFP_KERNEL >> - | __GFP_COMP /* compound page lets parts be mapped */ >> | __GFP_NORETRY /* don't trigger OOM-killer */ >> | __GFP_NOWARN; /* no stack trace print - this call is non-critical */ >> dmab->area = dma_alloc_coherent(dmab->dev.dev, size, &dmab->addr,
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