[PATCH] print vmalloc() state after allocation failures

[PATCH] print vmalloc() state after allocation failures

[Dave Hansen]

I was tracking down a page allocation failure that ended up in vmalloc().
Since vmalloc() uses 0-order pages, if somebody asks for an insane amount
of memory, we'll still get a warning with "order:0" in it.  That's not
very useful.

During recovery, vmalloc() also nicely frees all of the memory that it
got up to the point of the failure.  That is wonderful, but it also
quickly hides any issues.  We have a much different sitation if vmalloc()
repeatedly fails 10GB in to:

	vmalloc(100 * 1<<30);

versus repeatedly failing 4096 bytes in to a:

	vmalloc(8192);

This will print out messages that look like this:

[   30.040774] bash: vmalloc failure allocating after 0 / 73728 bytes

As a side issue, I also noticed that ctl_ioctl() does vmalloc() based
solely on an unverified value passed in from userspace.  Granted, it's
under CAP_SYS_ADMIN, but it still frightens me a bit.

multipathd: page allocation failure. order:0, mode:0xd2
Call Trace:
[c0000000f34ef570] [c000000000012d84] .show_stack+0x74/0x1c0 (unreliable)
[c0000000f34ef620] [c000000000159ed4] .__alloc_pages_nodemask+0x574/0x830
[c0000000f34ef7a0] [c00000000019306c] .alloc_pages_current+0x8c/0x110
[c0000000f34ef840] [c000000000183bdc] .__vmalloc_area_node+0x17c/0x220
[c0000000f34ef900] [d00000000132bb24] .copy_params+0x74/0xc0 [dm_mod]
[c0000000f34efad0] [d00000000132bcec] .ctl_ioctl+0x17c/0x2c0 [dm_mod]
[c0000000f34efb90] [d00000000132be48] .dm_ctl_ioctl+0x18/0x30 [dm_mod]
[c0000000f34efc00] [c0000000001c4ee4] .vfs_ioctl+0x54/0x140
[c0000000f34efc90] [c0000000001c5130] .do_vfs_ioctl+0x90/0x7c0
[c0000000f34efd80] [c0000000001c5914] .SyS_ioctl+0xb4/0xd0
[c0000000f34efe30] [c00000000000852c] syscall_exit+0x0/0x40
Mem-Info:
Node 0 DMA per-cpu:
...


Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>
---

 linux-2.6.git-dave/mm/vmalloc.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

diff -puN mm/vmalloc.c~vmalloc-warn mm/vmalloc.c
--- linux-2.6.git/mm/vmalloc.c~vmalloc-warn	2011-04-07 10:21:27.792401938 -0700
+++ linux-2.6.git-dave/mm/vmalloc.c	2011-04-07 10:21:27.800401934 -0700
@@ -1579,6 +1579,18 @@ static void *__vmalloc_area_node(struct 
 	return area->addr;
 
 fail:
+	if (!(gfp_mask & __GFP_NOWARN) && printk_ratelimit()) {
+		/*
+		 * We probably did a show_mem() and a stack dump above
+		 * inside of alloc_page*().  This is only so we can
+		 * tell how big the vmalloc() really was.  This will
+		 * also not be exactly the same as what was passed
+		 * to vmalloc() due to alignment and the guard page.
+		 */
+		printk(KERN_WARNING "%s: vmalloc: allocation failure, "
+			"allocated %ld of %ld bytes\n", current->comm,
+			(area->nr_pages*PAGE_SIZE), area->size);
+	}
 	vfree(area->addr);
 	return NULL;
 }
_

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Re: [PATCH] print vmalloc() state after allocation failures

[David Rientjes]

On Thu, 7 Apr 2011, Dave Hansen wrote:

> 
> I was tracking down a page allocation failure that ended up in vmalloc().
> Since vmalloc() uses 0-order pages, if somebody asks for an insane amount
> of memory, we'll still get a warning with "order:0" in it.  That's not
> very useful.
> 
> During recovery, vmalloc() also nicely frees all of the memory that it
> got up to the point of the failure.  That is wonderful, but it also
> quickly hides any issues.  We have a much different sitation if vmalloc()
> repeatedly fails 10GB in to:
> 
> 	vmalloc(100 * 1<<30);
> 
> versus repeatedly failing 4096 bytes in to a:
> 
> 	vmalloc(8192);
> 
> This will print out messages that look like this:
> 
> [   30.040774] bash: vmalloc failure allocating after 0 / 73728 bytes
> 

Won't it print "bash: vmalloc: allocation failure, allocated 0 of 73728 
bytes" instead?

> As a side issue, I also noticed that ctl_ioctl() does vmalloc() based
> solely on an unverified value passed in from userspace.  Granted, it's
> under CAP_SYS_ADMIN, but it still frightens me a bit.
> 
> multipathd: page allocation failure. order:0, mode:0xd2
> Call Trace:
> [c0000000f34ef570] [c000000000012d84] .show_stack+0x74/0x1c0 (unreliable)
> [c0000000f34ef620] [c000000000159ed4] .__alloc_pages_nodemask+0x574/0x830
> [c0000000f34ef7a0] [c00000000019306c] .alloc_pages_current+0x8c/0x110
> [c0000000f34ef840] [c000000000183bdc] .__vmalloc_area_node+0x17c/0x220
> [c0000000f34ef900] [d00000000132bb24] .copy_params+0x74/0xc0 [dm_mod]
> [c0000000f34efad0] [d00000000132bcec] .ctl_ioctl+0x17c/0x2c0 [dm_mod]
> [c0000000f34efb90] [d00000000132be48] .dm_ctl_ioctl+0x18/0x30 [dm_mod]
> [c0000000f34efc00] [c0000000001c4ee4] .vfs_ioctl+0x54/0x140
> [c0000000f34efc90] [c0000000001c5130] .do_vfs_ioctl+0x90/0x7c0
> [c0000000f34efd80] [c0000000001c5914] .SyS_ioctl+0xb4/0xd0
> [c0000000f34efe30] [c00000000000852c] syscall_exit+0x0/0x40
> Mem-Info:
> Node 0 DMA per-cpu:
> ...
> 
> 
> Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>
> ---
> 
>  linux-2.6.git-dave/mm/vmalloc.c |   12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff -puN mm/vmalloc.c~vmalloc-warn mm/vmalloc.c
> --- linux-2.6.git/mm/vmalloc.c~vmalloc-warn	2011-04-07 10:21:27.792401938 -0700
> +++ linux-2.6.git-dave/mm/vmalloc.c	2011-04-07 10:21:27.800401934 -0700
> @@ -1579,6 +1579,18 @@ static void *__vmalloc_area_node(struct 
>  	return area->addr;
>  
>  fail:
> +	if (!(gfp_mask & __GFP_NOWARN) && printk_ratelimit()) {
> +		/*
> +		 * We probably did a show_mem() and a stack dump above
> +		 * inside of alloc_page*().  This is only so we can
> +		 * tell how big the vmalloc() really was.  This will
> +		 * also not be exactly the same as what was passed
> +		 * to vmalloc() due to alignment and the guard page.
> +		 */
> +		printk(KERN_WARNING "%s: vmalloc: allocation failure, "
> +			"allocated %ld of %ld bytes\n", current->comm,
> +			(area->nr_pages*PAGE_SIZE), area->size);
> +	}
>  	vfree(area->addr);
>  	return NULL;
>  }

Looks good.

Acked-by: David Rientjes <rientjes@google.com>

__vmalloc_area_node() can also be moved into __vmalloc_node_range() since 
that's its only caller if you're interested.

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Re: [PATCH] print vmalloc() state after allocation failures

[Johannes Weiner]

On Thu, Apr 07, 2011 at 10:23:02AM -0700, Dave Hansen wrote:
> Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>

I agree with this in general, but have some nitpicks.

> @@ -1579,6 +1579,18 @@ static void *__vmalloc_area_node(struct 
>  	return area->addr;
>  
>  fail:
> +	if (!(gfp_mask & __GFP_NOWARN) && printk_ratelimit()) {

There is a comment above the declaration of printk_ratelimit:

/*
 * Please don't use printk_ratelimit(), because it shares ratelimiting state
 * with all other unrelated printk_ratelimit() callsites.  Instead use
 * printk_ratelimited() or plain old __ratelimit().
 */

I realize that the page allocator does it the same way, but I think it
should probably be fixed in there, rather than spread any further.

> +		/*
> +		 * We probably did a show_mem() and a stack dump above
> +		 * inside of alloc_page*().  This is only so we can
> +		 * tell how big the vmalloc() really was.  This will
> +		 * also not be exactly the same as what was passed
> +		 * to vmalloc() due to alignment and the guard page.
> +		 */
> +		printk(KERN_WARNING "%s: vmalloc: allocation failure, "
> +			"allocated %ld of %ld bytes\n", current->comm,
> +			(area->nr_pages*PAGE_SIZE), area->size);
> +	}

To me, this does not look like something that should just be appended
to the whole pile spewed out by dump_stack() and show_mem().  What do
you think about doing the page allocation with __GFP_NOWARN and have
the full report come from this place, with the line you introduce as
leader?

	Hannes

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Re: [PATCH] print vmalloc() state after allocation failures

[Dave Hansen]

On Thu, 2011-04-07 at 17:19 -0700, Johannes Weiner wrote:
> On Thu, Apr 07, 2011 at 10:23:02AM -0700, Dave Hansen wrote:
> > @@ -1579,6 +1579,18 @@ static void *__vmalloc_area_node(struct 
> >  	return area->addr;
> >  
> >  fail:
> > +	if (!(gfp_mask & __GFP_NOWARN) && printk_ratelimit()) {
> 
> There is a comment above the declaration of printk_ratelimit:
> 
> /*
>  * Please don't use printk_ratelimit(), because it shares ratelimiting state
>  * with all other unrelated printk_ratelimit() callsites.  Instead use
>  * printk_ratelimited() or plain old __ratelimit().
>  */
> 
> I realize that the page allocator does it the same way, but I think it
> should probably be fixed in there, rather than spread any further.

You're the second person to mention this.  I should have listened the
first time. :)  I'll fix it up and repost.

> > +		/*
> > +		 * We probably did a show_mem() and a stack dump above
> > +		 * inside of alloc_page*().  This is only so we can
> > +		 * tell how big the vmalloc() really was.  This will
> > +		 * also not be exactly the same as what was passed
> > +		 * to vmalloc() due to alignment and the guard page.
> > +		 */
> > +		printk(KERN_WARNING "%s: vmalloc: allocation failure, "
> > +			"allocated %ld of %ld bytes\n", current->comm,
> > +			(area->nr_pages*PAGE_SIZE), area->size);
> > +	}
> 
> To me, this does not look like something that should just be appended
> to the whole pile spewed out by dump_stack() and show_mem().  What do
> you think about doing the page allocation with __GFP_NOWARN and have
> the full report come from this place, with the line you introduce as
> leader?

That sounds fine to me.  

-- Dave

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