Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756465AbaLIC5x (ORCPT ); Mon, 8 Dec 2014 21:57:53 -0500 Received: from mail-ie0-f180.google.com ([209.85.223.180]:55342 "EHLO mail-ie0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754760AbaLIC5w (ORCPT ); Mon, 8 Dec 2014 21:57:52 -0500 MIME-Version: 1.0 In-Reply-To: <10532762.PXKTQM8KjH@wuerfel> References: <1418027967-12923-1-git-send-email-acourbot@nvidia.com> <10532762.PXKTQM8KjH@wuerfel> From: Alexandre Courbot Date: Tue, 9 Dec 2014 11:57:22 +0900 Message-ID: Subject: Re: [PATCH] ARM: DMA: Fix kzalloc flags in __iommu_alloc_buffer() To: Arnd Bergmann Cc: "linux-arm-kernel@lists.infradead.org" , Alexandre Courbot , Russell King , Marek Szyprowski , Konrad Rzeszutek Wilk , Linux Kernel Mailing List , Thierry Reding Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/