From: Neil Brown <neilb@cse.unsw.edu.au>
Subject: Re: 2.6.3: oops reading /proc/net/rpc/auth.unix.ip/content
Date: Wed, 25 Feb 2004 10:01:12 +1100
Sender: nfs-admin@lists.sourceforge.net
Message-ID: <16443.55224.556737.70553@notabene.cse.unsw.edu.au>
References: <Pine.LNX.4.58.0402240909310.889@morpheus>
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Cc: nfs@lists.sourceforge.net
To: Burton Windle <bwindle@fint.org>
In-Reply-To: message from Burton Windle on Tuesday February 24
Errors-To: nfs-admin@lists.sourceforge.net

On Tuesday February 24, bwindle@fint.org wrote:
> Hello.  I just upgraded a workstation from 2.6.2 to 2.6.3, and am now
> seeing an oops on boot when my init scripts run the nfs-kernel-server
> script. The oops actually happens whenever trying to read
> /proc/net/rpc/auth.unix.ip/content
> 
> Is this a known-issue?

I hate to say this, but this cannot possibly happen :-)

It is fairly clear from:

> Unable to handle kernel NULL pointer dereference at virtual address 00000044
> EIP is at content_open+0x5b/0x80
> eax: 00000000   ebx: cfb49628   ecx: 00000000   edx: cf92d738
> esi: 00000000   edi: cfb29df4   ebp: cfc45f3c   esp: cfc45f28
> ds: 007b   es: 007b   ss: 0068
> 
> Code: 89 58 44 89 f0 8b 5d f4 8b 75 f8 8b 7d fc 89 ec 5d c3 8d 76
> 

that the oops is happening :

static int content_open(struct inode *inode, struct file *file)
{
	int res;
	struct handle *han;
	struct cache_detail *cd = PDE(inode)->data;

	han = kmalloc(sizeof(*han), GFP_KERNEL);
	if (han == NULL)
		return -ENOMEM;

	han->cd = cd;

	res = seq_open(file, &cache_content_op);
	if (res)
		kfree(han);
	else
/*HERE*/	((struct seq_file *)file->private_data)->private = han;

	return res;
}

The instruction that is oopsing is:
   0:   89 58 44                  mov    %ebx,0x44(%eax)
which is storing the value "han" (in %ebx, 0xcfb49628) into element
"private" (offset 0x44) of ((struct seq_file *)file->private_data)
(in %eax, 0x00).

So file->private_data must be NULL.

However seq_open has just returned zero (or we wouldn't have got to
this code) and you can see from

int seq_open(struct file *file, struct seq_operations *op)
{
	struct seq_file *p = kmalloc(sizeof(*p), GFP_KERNEL);
	if (!p)
		return -ENOMEM;
	memset(p, 0, sizeof(*p));
	sema_init(&p->sem, 1);
	p->op = op;
	file->private_data = p;
	return 0;
}

that this means that file->private_data is most definitely not NULL.

As I said, it cannot happen....

Maybe a compiler bug ???? (wouldn't be the first time).

Would you be able to use gdb to disassemble all of content_open and
seq_file so I can see what is happening?

NeilBrown


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