On Fri, 2011-09-09 at 18:40 +0530, R, Sricharan wrote:
> Sorry resending again. My mailer settings thrashed my earlier email.
>
> Hi,
> A kernel crash is observed on 3.1rc4 kernel when HIGHMEM is enabled and
> kernel is booted with a NFS on omap4430sdp. The issue happens in the below
> scenario.
>
> In file net/sunrpc/xprtsock.c,
> static int xs_send_pagedata( xxx, struct xdr_buf *xdr, ..)
> {
> Struct page **ppage;
> ....
> .....
> ppage = xdr->pages + (base >> PAGE_SHIFT);
> ....
> err = sock->ops->sendpage(sock, *ppage, base, len, flags);
>
> ...
> }
>
> 1) In the above piece of code, the *ppage value from ops->sendpage
> function is finally passed on to Kmap by the lower level code to
> get the virtual address of the page.
> 2) In some corner cases the value of *ppage pointer is NULL.
> 3) When highmem is enabled and a NULL pointer is passed to
> Kmap, then kmap finally crashes. But in the case when highmem
> is disabled, then kmap returns a junk value for NULL pointer.
>
> Highmem Enabled , kmap( NULL )-----> kernel crashes.
>
> Highmem disabled, kmap( NULL )-----> junk value is returned.
> Subsequently this message is observed on
> the console.
>
> "RPC call returned error 14"
>
> 4) Now the question is why is the value of *ppage = NULL is passed
> from the above piece of code to lower layers.
> Should that not have handled *ppage = NULL? and kmap should not
> have received a NULL pointer?
I wouldn't expect *ppage to be NULL under any circumstances, so I'm
really curious as to what is happening here.
Could you perhaps add a printk() to that section of code to print out
the values of 'xdr->page_base', 'xdr->page_len', 'len' and 'remainder'
in the case where *ppage == NULL?
Cheers
Trond
--
Trond Myklebust
Linux NFS client maintainer
NetApp
[email protected]
www.netapp.com
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