Re: DMA memory, split_page, BUG_ON(PageCompound()), sound

[Marc Singer <elf@buici.com>]

On Tue, Jul 11, 2006 at 03:34:11AM +1000, Nick Piggin wrote:
> >So I'll mask off __GFP_COMP for the time being in the ARM dma allocator
> >with a note to this effect?
> 
> I believe that should do the trick, yes (AFAIK, nobody yet is
> explicitly relying on a compound page from the dma allocator).
> 
> Marc can hopefully confim the fix.

The patch, attached, works in that there is no BUG_ON() trap.

>From c13ac90b1dd6e5fab63182ce323673cdffb0b55f Mon Sep 17 00:00:00 2001
Date: Mon, 10 Jul 2006 19:38:47 -0700
Subject: [PATCH] Drop __GFP_COMP for DMA memory allocations
---
 arch/arm/mm/consistent.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

Hack for incompatible __GFP_COMP flag making its way into the ARM DMA
consistent memory allocator.

Signed-off-by: Marc Singer <elf@buici.com>

diff --git a/arch/arm/mm/consistent.c b/arch/arm/mm/consistent.c
index 50e6b6b..7b7cc4e 100644
--- a/arch/arm/mm/consistent.c
+++ b/arch/arm/mm/consistent.c
@@ -153,6 +153,13 @@ __dma_alloc(struct device *dev, size_t s
 	unsigned long order;
 	u64 mask = ISA_DMA_THRESHOLD, limit;
 
+	/* Following is a work-around (a.k.a. hack) to prevent pages
+	 * with __GFP_COMP being passed to split_page() which cannot
+	 * handle them.  The real problem is that this flag probably
+	 * should be 0 on ARM as it is not supported on this
+	 * platform--see CONFIG_HUGETLB_PAGE. */
+	gfp &= ~(__GFP_COMP);
+
 	if (!consistent_pte[0]) {
 		printk(KERN_ERR "%s: not initialised\n", __func__);
 		dump_stack();
-- 
1.4.0