[linux-cifs-client] Re: [PATCH] cifs: prevent cifs_writepages() from skipping unwritten pages

[Jeff Layton]

On Mon, 17 Nov 2008 07:02:47 -0600
Dave Kleikamp <shaggy at linux.vnet.ibm.com> wrote:

> cifs: prevent cifs_writepages() from skipping unwritten pages
> 
> In order to write contiguous pages whenever possible, cifs_writepages()
> asks pagevec_lookup_tag() for more pages than it may write at one time.
> Normally, it then resets index just past the last page written before calling
> pagevec_lookup_tag() again.
> 
> If cifs_writepages() can't write the first page returned, it wasn't resetting
> index, and the next call to pagevec_lookup_tag() resulted in skipping all of
> the pages it previously returned, even though cifs_writepages() did nothing
> with them.  This can result in data loss when the file descriptor is about
> to be closed.
> 
> This patch ensures that index gets set back to the first returned page so
> that none get skipped.
> 
> Signed-off-by: Dave Kleikamp <shaggy at linux.vnet.ibm.com>
> Cc: Shirish S Pargaonkar <shirishp at us.ibm.com>
> Cc: Steve French <sfrench at us.ibm.com>
> Cc: Jeff Layton <jlayton at redhat.com>
> 
> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> index 1540ada..9815e03 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -1404,7 +1404,10 @@ retry:
>  			if ((wbc->nr_to_write -= n_iov) <= 0)
>  				done = 1;
>  			index = next;
> -		}
> +		} else
> +			/* Need to re-find the pages we skipped */
> +			index = pvec.pages[0]->index;
> +
>  		pagevec_release(&pvec);
>  	}
>  	if (!scanned && !done) {
> 

Patch looks sane to me and fairly obvious once you know what you're looking for...

Do we know what condition is occurring to make it break out of the loop before n_iov can be incremented?

-- 
Jeff Layton <jlayton at redhat.com>