linux-kernel - Re: suppress page allocation failure warnings from sys

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Message-Id: <20120327155149.d41a235b.akpm@linux-foundation.org>
Date:	Tue, 27 Mar 2012 15:51:49 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dave Jones <davej@...hat.com>
Cc:	viro@...iv.linux.org.uk,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: suppress page allocation failure warnings from sys_listxattr

On Tue, 13 Mar 2012 14:22:20 -0400
Dave Jones <davej@...hat.com> wrote:

> This size is user controllable, and so it's trivial for someone to trigger a
> stream of order:4 page allocation errors.
> 
> Signed-off-by: Dave Jones <davej@...hat.com>
> 
> --- 
> There's also a similar problem in setxattr, but I'm not sure how we want
> to pass NOWARN down to memdup_user. Thoughts ?
> 
> diff --git a/fs/xattr.c b/fs/xattr.c
> index 82f4337..544df90 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -496,7 +496,7 @@ listxattr(struct dentry *d, char __user *list, size_t size)
>  	if (size) {
>  		if (size > XATTR_LIST_MAX)
>  			size = XATTR_LIST_MAX;
> -		klist = kmalloc(size, GFP_KERNEL);
> +		klist = kmalloc(size, __GFP_NOWARN | GFP_KERNEL);
>  		if (!klist)
>  			return -ENOMEM;
>  	}

hm.  The patch is good, but one would hope that it isn't "trivial" to
trigger a page allocation failure for a kmalloc(65536, GFP_KERNEL) -
the VM is supposed to be able to handle that.

Is it really *that* easy, or is Something Unusual happening with that
machine?
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