[PATCH] adjust gfp mask passed on nested vmalloc() invocation

[PATCH] adjust gfp mask passed on nested vmalloc() invocation

[Jan Beulich]

- fix a latent bug resulting from blindly or-ing in __GFP_ZERO, since
  the combination of this and __GFP_HIGHMEM (possibly passed into the
  function) is forbidden in interrupt context
- avoid wasting more precious resources (DMA or DMA32 pools), when
  being called through vmalloc_32{,_user}()
- explicitly allow using high memory here even if the outer allocation
  request doesn't allow it, unless is collides with __GFP_ZERO

Signed-off-by: Jan Beulich <jbeulich@novell.com>

---
 mm/vmalloc.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- linux-2.6.32-rc3/mm/vmalloc.c	2009-10-05 11:59:56.000000000 +0200
+++ 2.6.32-rc3-vmalloc-nested-gfp/mm/vmalloc.c	2009-10-05 08:40:36.000000000 +0200
@@ -1410,6 +1410,7 @@ static void *__vmalloc_area_node(struct 
 {
 	struct page **pages;
 	unsigned int nr_pages, array_size, i;
+	gfp_t nested_gfp = (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO;
 
 	nr_pages = (area->size - PAGE_SIZE) >> PAGE_SHIFT;
 	array_size = (nr_pages * sizeof(struct page *));
@@ -1417,13 +1418,16 @@ static void *__vmalloc_area_node(struct 
 	area->nr_pages = nr_pages;
 	/* Please note that the recursion is strictly bounded. */
 	if (array_size > PAGE_SIZE) {
-		pages = __vmalloc_node(array_size, gfp_mask | __GFP_ZERO,
+#ifdef CONFIG_HIGHMEM
+		/* See the comment in prep_zero_page(). */
+		if (!in_interrupt())
+			nested_gfp |= __GFP_HIGHMEM;
+#endif
+		pages = __vmalloc_node(array_size, nested_gfp,
 				PAGE_KERNEL, node, caller);
 		area->flags |= VM_VPAGES;
 	} else {
-		pages = kmalloc_node(array_size,
-				(gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO,
-				node);
+		pages = kmalloc_node(array_size, nested_gfp, node);
 	}
 	area->pages = pages;
 	area->caller = caller;



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Re: [PATCH] adjust gfp mask passed on nested vmalloc() invocation

[Hugh Dickins]

On Mon, 5 Oct 2009, Jan Beulich wrote:

> - fix a latent bug resulting from blindly or-ing in __GFP_ZERO, since
>   the combination of this and __GFP_HIGHMEM (possibly passed into the
>   function) is forbidden in interrupt context
> - avoid wasting more precious resources (DMA or DMA32 pools), when
>   being called through vmalloc_32{,_user}()
> - explicitly allow using high memory here even if the outer allocation
>   request doesn't allow it, unless is collides with __GFP_ZERO
> 
> Signed-off-by: Jan Beulich <jbeulich@novell.com>

I thought vmalloc.c was a BUG_ON(in_interrupt()) zone?
The locking is all spin_lock stuff, not spin_lock_irq stuff.
That's probably why your "bug" has remained "latent".

Using HIGHMEM for internal arrays looks reasonable to me; but if
__GFP_ZERO were a problem, wouldn't it be much cleaner to skip the
"unless it collides" and #ifdef CONFIG_HIGHMEM !in_interrupt() stuff,
just memset the array returned from __vmalloc_node()?

Hugh

> 
> ---
>  mm/vmalloc.c |   12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> --- linux-2.6.32-rc3/mm/vmalloc.c	2009-10-05 11:59:56.000000000 +0200
> +++ 2.6.32-rc3-vmalloc-nested-gfp/mm/vmalloc.c	2009-10-05 08:40:36.000000000 +0200
> @@ -1410,6 +1410,7 @@ static void *__vmalloc_area_node(struct 
>  {
>  	struct page **pages;
>  	unsigned int nr_pages, array_size, i;
> +	gfp_t nested_gfp = (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO;
>  
>  	nr_pages = (area->size - PAGE_SIZE) >> PAGE_SHIFT;
>  	array_size = (nr_pages * sizeof(struct page *));
> @@ -1417,13 +1418,16 @@ static void *__vmalloc_area_node(struct 
>  	area->nr_pages = nr_pages;
>  	/* Please note that the recursion is strictly bounded. */
>  	if (array_size > PAGE_SIZE) {
> -		pages = __vmalloc_node(array_size, gfp_mask | __GFP_ZERO,
> +#ifdef CONFIG_HIGHMEM
> +		/* See the comment in prep_zero_page(). */
> +		if (!in_interrupt())
> +			nested_gfp |= __GFP_HIGHMEM;
> +#endif
> +		pages = __vmalloc_node(array_size, nested_gfp,
>  				PAGE_KERNEL, node, caller);
>  		area->flags |= VM_VPAGES;
>  	} else {
> -		pages = kmalloc_node(array_size,
> -				(gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO,
> -				node);
> +		pages = kmalloc_node(array_size, nested_gfp, node);
>  	}
>  	area->pages = pages;
>  	area->caller = caller;

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Re: [PATCH] adjust gfp mask passed on nested vmalloc() invocation

[Jan Beulich]

>>> Hugh Dickins <hugh.dickins@tiscali.co.uk> 06.10.09 23:58 >>>
>On Mon, 5 Oct 2009, Jan Beulich wrote:
>
>> - fix a latent bug resulting from blindly or-ing in __GFP_ZERO, since
>>   the combination of this and __GFP_HIGHMEM (possibly passed into the
>>   function) is forbidden in interrupt context
>> - avoid wasting more precious resources (DMA or DMA32 pools), when
>>   being called through vmalloc_32{,_user}()
>> - explicitly allow using high memory here even if the outer allocation
>>   request doesn't allow it, unless is collides with __GFP_ZERO
>> 
>> Signed-off-by: Jan Beulich <jbeulich@novell.com>
>
>I thought vmalloc.c was a BUG_ON(in_interrupt()) zone?
>The locking is all spin_lock stuff, not spin_lock_irq stuff.
>That's probably why your "bug" has remained "latent".

Then you probably mean BUG_ON(irqs_disabled()), which would seem
correct. But if the gfp mask massaging was needed for calling kmalloc(),
it would seem odd that the same shouldn't be needed for calling
vmalloc() recursively...

>Using HIGHMEM for internal arrays looks reasonable to me; but if
>__GFP_ZERO were a problem, wouldn't it be much cleaner to skip the
>"unless it collides" and #ifdef CONFIG_HIGHMEM !in_interrupt() stuff,
>just memset the array returned from __vmalloc_node()?

The main goal was to change the existing code as little as possible - I
did consider this alternative, but wasn't sure that would be accepted.
If you view this as the better alternative, I'll certainly modify the
patch to do it that way.

Jan

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Re: [PATCH] adjust gfp mask passed on nested vmalloc() invocation

[Jan Beulich]

>>> Hugh Dickins <hugh.dickins@tiscali.co.uk> 06.10.09 23:58 >>>
>On Mon, 5 Oct 2009, Jan Beulich wrote:
>
>> - fix a latent bug resulting from blindly or-ing in __GFP_ZERO, since
>>   the combination of this and __GFP_HIGHMEM (possibly passed into the
>>   function) is forbidden in interrupt context
>> - avoid wasting more precious resources (DMA or DMA32 pools), when
>>   being called through vmalloc_32{,_user}()
>> - explicitly allow using high memory here even if the outer allocation
>>   request doesn't allow it, unless is collides with __GFP_ZERO
>> 
>> Signed-off-by: Jan Beulich <jbeulich@novell.com>
>
>I thought vmalloc.c was a BUG_ON(in_interrupt()) zone?
>The locking is all spin_lock stuff, not spin_lock_irq stuff.
>That's probably why your "bug" has remained "latent".

Actually, my previous reply to this was bogus, and I agree with your
statement. Hence, from a second version of the patch (depending on
your response on my question regarding the other part of your reply),
I should drop that part of the description.

Jan

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Re: [PATCH] adjust gfp mask passed on nested vmalloc() invocation

[Hugh Dickins]

On Wed, 7 Oct 2009, Jan Beulich wrote:
> >>> Hugh Dickins <hugh.dickins@tiscali.co.uk> 06.10.09 23:58 >>>
> >On Mon, 5 Oct 2009, Jan Beulich wrote:
> >
> >> - fix a latent bug resulting from blindly or-ing in __GFP_ZERO, since
> >>   the combination of this and __GFP_HIGHMEM (possibly passed into the
> >>   function) is forbidden in interrupt context
> >> - avoid wasting more precious resources (DMA or DMA32 pools), when
> >>   being called through vmalloc_32{,_user}()
> >> - explicitly allow using high memory here even if the outer allocation
> >>   request doesn't allow it, unless is collides with __GFP_ZERO
> >> 
> >> Signed-off-by: Jan Beulich <jbeulich@novell.com>
> >
> >I thought vmalloc.c was a BUG_ON(in_interrupt()) zone?
> >The locking is all spin_lock stuff, not spin_lock_irq stuff.
> >That's probably why your "bug" has remained "latent".
> 
> Then you probably mean BUG_ON(irqs_disabled()), which would seem
> correct.

I'm relieved you came to see that remark as bogus.

> But if the gfp mask massaging was needed for calling kmalloc(),
> it would seem odd that the same shouldn't be needed for calling
> vmalloc() recursively...
> 
> >Using HIGHMEM for internal arrays looks reasonable to me; but if
> >__GFP_ZERO were a problem, wouldn't it be much cleaner to skip the
> >"unless it collides" and #ifdef CONFIG_HIGHMEM !in_interrupt() stuff,
> >just memset the array returned from __vmalloc_node()?
> 
> The main goal was to change the existing code as little as possible - I
> did consider this alternative, but wasn't sure that would be accepted.
> If you view this as the better alternative, I'll certainly modify the
> patch to do it that way.

Well, now we've accepted that this code cannot be used in_interrupt(),
there's no need for your #ifdef CONFIG_HIGHMEM nor for my memset: just
use __GFP_ZERO as it was before, and your patch would amount to or'ing
__GFP_HIGHMEM into gfp_mask for the __vmalloc_node case - wouldn't it?

Hugh

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Re: [PATCH] adjust gfp mask passed on nested vmalloc() invocation

[Jan Beulich]

>>> Hugh Dickins <hugh.dickins@tiscali.co.uk> 07.10.09 14:08 >>>
>Well, now we've accepted that this code cannot be used in_interrupt(),
>there's no need for your #ifdef CONFIG_HIGHMEM nor for my memset: just
>use __GFP_ZERO as it was before, and your patch would amount to or'ing
>__GFP_HIGHMEM into gfp_mask for the __vmalloc_node case - wouldn't it?

Plus the consolidation of masking the passed in gfp_mask by
GFP_RECLAIM_MASK also for the nested vmalloc() case, in particular to
remove the GFP_DMA* possibly coming in from vmalloc_32(). But yes,
it will become simpler.

Jan

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