Messages in this thread | | | From | Alexandre Courbot <> | Date | Tue, 9 Dec 2014 11:57:22 +0900 | Subject | Re: [PATCH] ARM: DMA: Fix kzalloc flags in __iommu_alloc_buffer() |
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On Mon, Dec 8, 2014 at 7:24 PM, Arnd Bergmann <arnd@arndb.de> wrote: > On Monday 08 December 2014 17:39:27 Alexandre Courbot wrote: >> There doesn't seem to be any valid reason to allocate the pages array >> with the same flags as the buffer itself. Doing so can eventually lead >> to the following safeguard in mm/slab.c to be hit: >> >> BUG_ON(flags & GFP_SLAB_BUG_MASK); >> >> This happens when buffers are allocated with __GFP_DMA32 or >> __GFP_HIGHMEM. >> >> Fix this by allocating the pages array with GFP_KERNEL to follow what is >> done elsewhere in this file. Using GFP_KERNEL in __iommu_alloc_buffer() >> is safe because atomic allocations are handled by __iommu_alloc_atomic(). >> > > I think you need to carry over the GFP_ATOMIC flag if that is set by the > caller, but not the GFP_HIGHMEM or GFP_DMA32. Not sure if it's better > to mask out flags from the caller mask, or to start with GFP_KERNEL > and adding in extra bits.
I thought the issue of atomicity is already handled by __iommu_alloc_buffer's caller (arm_iommu_alloc_attrs):
if (!(gfp & __GFP_WAIT)) return __iommu_alloc_atomic(dev, size, handle); .... pages = __iommu_alloc_buffer(dev, size, gfp, attrs);
Isn't the interesting property about GFP_ATOMIC that it does not include __GFP_WAIT? I may very well misunderstand the issue, sorry if that's the case.
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