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Date: Fri, 07 Aug 2009 12:20:03 +0300
From: Adrian Hunter <adrian.hunter@nokia.com>
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To: JiSheng Zhang <jszhang3@gmail.com>
Subject: Re: [UBI UBIFS] replace vmalloc with kmalloc
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JiSheng Zhang wrote:
> If nandflash driver use DMA to support UBI and UBIFS i/o, there will
> be panic like
> the following. This is because UBI and UBIFS use vmalloced buffer
> somewhere while
> nandflash driver put the buffer under DMA and DMA support doesn't like vmalloced
> memory.
> [  412.369280] UBIFS: default file-system created
> [  412.374879] Unable to handle kernel NULL pointer dereference at
> virtual address 00000000
> [  412.383177] UBIFS: background thread "ubifs_bgt0_0" started, PID 887
> [  412.389656] pgd = c0004000
> [  412.392419] [00000000] *pgd=00000000
> [  412.396117] Internal error: Oops: 817 [#1] PREEMPT
> 
> Yes, I know kmalloc may fail when memory get fragmented, but I grep the UBI and
> UBIFS's source, there are six .c files and seven .c files using
> vmalloc, the function
> which call vmalloc are all called during the ubi being attached and
> the volume being
> mounted. In embedded system, this mainly happen during kernel boot, it
> should succeed.
> 
> After replacing vmalloc with kmalloc, ubi and ubifs runs fine on my
> board. I can alos upload
> a patch.
> 
> Comments are welcomed!

vmalloc allows large (> 128KiB) buffers, but kmalloc doesn't.
So we presently have no choice but to use vmalloc.

I do not know what hardware you have or exactly what driver you
are using, but we have UBIFS on OneNAND using DMA.
See drivers/mtd/onenand/omap2.c