Messages in this thread | | | Date | Mon, 25 Jun 2007 15:55:05 +0200 | From | Nicolas Ferre <> | Subject | Re: Oops in a driver while using SLUB as a SLAB allocator |
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Hugh Dickins : > On Sun, 24 Jun 2007, Russell King wrote: >> On Sun, Jun 24, 2007 at 11:24:16AM +0100, Hugh Dickins wrote: >>> On Sun, 24 Jun 2007, Russell King wrote: >>>> On Fri, Jun 22, 2007 at 07:39:33PM +0100, Hugh Dickins wrote: >>>> >>>> Please forward the original problem report. >>> Done. >> Okay, that seems to back up my suspicions - it's definitely AT91-based. >> Since AT91-based machines do not have a DMA coherent cache, >> arch_is_coherent() must be defined to '0'. The only way that kmalloc >> could be reached is if that were defined to something other than '0', >> and if that's done on a machine with DMA incoherent caches, that will >> lead to data corruption. > > Yes, having looked through that now, I agree with you 100%.
AT91 _is_ defined with the arch_is_coherent() switch set to 0 (in include/asm-arm/memory.h and not overloaded).
>> I think we need to wait for Nicolas to respond on this issue before >> running headlong into applying a sticky plaster for something which is >> actually a deeper issue. > > No need for Nicolas to respond, I think I've found what's "wrong": > see below. > >> However, the arch_is_coherent() path _is_ buggy as it stands, but in >> more than the way identified thus far. Eg, it doesn't set __GFP_DMA >> appropriately for various DMA masks, so it might return DMA inaccessible >> memory.
Ok it is bad but, in AT91, all memory is accessible with DMA.
[..]
> The slub allocation which gives rise to Nicolas' oops in not in > ARM, but (I'm guessing) in drivers/mmc/core/sd.c: one of those > status = kmalloc(64, GFP_KERNEL); > where status is passed down for the response from mmc_sd_switch.
True, the oops appears after a mmc switch command (#6 command).
[..]
Not sure I can add much to what Hugh has said. If you need some more precision anyway, I will try to answer.
Regards, -- Nicolas Ferre
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