From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Tue, 09 Dec 2014 09:14:36 +0100 Subject: [PATCH] ARM: DMA: Fix kzalloc flags in __iommu_alloc_buffer() In-Reply-To: References: <1418027967-12923-1-git-send-email-acourbot@nvidia.com> <10532762.PXKTQM8KjH@wuerfel> Message-ID: <34381031.ms2E1cJuQN@wuerfel> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tuesday 09 December 2014 11:57:22 Alexandre Courbot wrote: > On Mon, Dec 8, 2014 at 7:24 PM, Arnd Bergmann 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. No, I think you are right, I wasn't looking at the whole call chain, just at your patch, and it looks good to me now. Arnd