Re: 2.6.15-rc1-mm2 -- Bad page state at free_hot_cold_page (in process 'aplay', page c18eef30)

[Takashi Iwai <tiwai@suse.de>]

Hi Hugh,

At Sun, 20 Nov 2005 19:35:57 +0000 (GMT),
Hugh Dickins wrote:
> 
> On Sun, 20 Nov 2005, Lee Revell wrote:
> > (Added alsa-devel to cc:)
> > 
> > Will this change have any ill effects on older kernels?
> 
> I think not (except 2.6.5 and earlier didn't define __GFP_COMP).

Sorry, I still don't figure out how __GFP_COMP solved this problem.
Could you enlighten me a bit?

Isn't it needed for dma_alloc_coherent() (for i386, particularly),
too?  dma_alloc_coherent() also gets pages with __get_free_pages().

Also, I think we can remove all Set/ClearPageReserved() in memalloc.c
now.  It was there just for mmap...


> > If not we should fix it in the ALSA tree right?
> 
> Probably, but I'm no authority on the ALSA tree.

We'd need to add a dummy definition of __GFP_COMP for older kenels in
alsa-driver tree.  But that's all.

> And suggest you wait a bit, since I haven't yet signed off on the
> patch that piece will be a part of.
> 
> And what about the patch at the bottom (which I had CC'ed to Karsten
> Wiese), is that part of the ALSA tree too?  That case isn't so easy:
> the get_page makes a difference, and probably it was right not to do
> it before, yet strange it was the only nopage in the tree which didn't
> get_page.

In the ealier version, get_page() in sound/pcm_native.c was checked
with "if (! PageReserved(page))".  Since the pages were always
reserved, get_page was never called indeed.  (IIRC, the check was
introduced to avoid crash with anon page or so.)
usx2y driver was added later, so it didn't have unneeded get_page().


thanks,

Takashi

> 
> Hugh
> 
> > Lee
> > 
> > On Sun, 2005-11-20 at 08:05 +0000, Hugh Dickins wrote:
> > > On Sat, 19 Nov 2005, Miles Lane wrote:
> > > > [17179671.700000] Bad page state at free_hot_cold_page (in process
> > > > 'aplay', page c18eef30)
> > > > [17179671.700000] flags:0x80000414 mapping:00000000 mapcount:0 count:0
> > > 
> > > Please let me know if it's not fixed by:
> > > 
> > > --- 2.6.15-rc1-mm2/sound/core/memalloc.c	2005-11-12 09:01:28.000000000 +0000
> > > +++ linux/sound/core/memalloc.c	2005-11-19 19:03:32.000000000 +0000
> > > @@ -197,6 +197,7 @@ void *snd_malloc_pages(size_t size, gfp_
> > >  
> > >  	snd_assert(size > 0, return NULL);
> > >  	snd_assert(gfp_flags != 0, return NULL);
> > > +	gfp_flags |= __GFP_COMP;	/* compound page lets parts be mapped */
> > >  	pg = get_order(size);
> > >  	if ((res = (void *) __get_free_pages(gfp_flags, pg)) != NULL) {
> > >  		mark_pages(virt_to_page(res), pg);
> > > @@ -241,6 +242,7 @@ static void *snd_malloc_dev_pages(struct
> > >  	snd_assert(dma != NULL, return NULL);
> > >  	pg = get_order(size);
> > >  	gfp_flags = GFP_KERNEL
> > > +		| __GFP_COMP	/* compound page lets parts be mapped */
> > >  		| __GFP_NORETRY /* don't trigger OOM-killer */
> > >  		| __GFP_NOWARN; /* no stack trace print - this call is non-critical */
> > >  	res = dma_alloc_coherent(dev, PAGE_SIZE << pg, dma, gfp_flags);
> 
> Karsten Wiese <annabellesgarden@yahoo.de>
> [PATCH 03/11] unpaged: sound nopage get_page
> 
> Something noticed when studying use of VM_RESERVED in different drivers:
> snd_usX2Y_hwdep_pcm_vm_nopage omitted to get_page: fixed.
> 
> And how did this work before?  Aargh!  That nopage is returning a page
> from within a buffer allocated by snd_malloc_pages, which allocates a
> high-order page, then does SetPageReserved on each 0-order page within.
> 
> That would have worked in 2.6.14, because when the area was unmapped,
> PageReserved inhibited put_page.  2.6.15-rc1 removed that inhibition
> (while leaving ineffective PageReserveds around for now), but it hasn't
> caused trouble because.. we've not been freeing from VM_RESERVED at all.
> 
> Signed-off-by: Hugh Dickins <hugh@veritas.com>
> ---
> 
>  sound/usb/usx2y/usx2yhwdeppcm.c |    1 +
>  1 files changed, 1 insertion(+)
> 
> --- unpaged02/sound/usb/usx2y/usx2yhwdeppcm.c	2005-11-12 09:01:30.000000000 +0000
> +++ unpaged03/sound/usb/usx2y/usx2yhwdeppcm.c	2005-11-17 15:10:34.000000000 +0000
> @@ -691,6 +691,7 @@ static struct page * snd_usX2Y_hwdep_pcm
>  	snd_assert((offset % PAGE_SIZE) == 0, return NOPAGE_OOM);
>  	vaddr = (char*)((usX2Ydev_t*)area->vm_private_data)->hwdep_pcm_shm + offset;
>  	page = virt_to_page(vaddr);
> +	get_page(page);
>  
>  	if (type)
>  		*type = VM_FAULT_MINOR;
> -
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