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

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Date:	Thu, 7 Apr 2011 15:11:28 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] print vmalloc() state after allocation failures

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@...ux.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@...gle.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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