Re: [PATCH v3 1/2] afs: Fix afs_write_end() to handle short writes

[Matthew Wilcox]

On Mon, Jun 21, 2021 at 04:40:17PM +0100, David Howells wrote:
> Fix afs_write_end() to correctly handle a short copy into the intended
> write region of the page.  Two things are necessary:
> 
>  (1) If the page is not up to date, then we should just return 0
>      (ie. indicating a zero-length copy).  The loop in
>      generic_perform_write() will go around again, possibly breaking up the
>      iterator into discrete chunks[1].
> 
>      This is analogous to commit b9de313cf05fe08fa59efaf19756ec5283af672a
>      for ceph.
> 
>  (2) The page should not have been set uptodate if it wasn't completely set
>      up by netfs_write_begin() (this will be fixed in the next patch), so
>      we need to set uptodate here in such a case.
> 
> Also remove the assertion that was checking that the page was set uptodate
> since it's now set uptodate if it wasn't already a few lines above.  The
> assertion was from when uptodate was set elsewhere.
> 
> Changes:
> v3: Remove the handling of len exceeding the end of the page.
> 
> Fixes: 3003bbd0697b ("afs: Use the netfs_write_begin() helper")
> Reported-by: Jeff Layton <jlayton@xxxxxxxxxx>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
> cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> cc: linux-afs@xxxxxxxxxxxxxxxxxxx
> Link: https://lore.kernel.org/r/YMwVp268KTzTf8cN@xxxxxxxxxxxxxxxxxxxxx/ [1]
> Link: https://lore.kernel.org/r/162367682522.460125.5652091227576721609.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v1
> Link: https://lore.kernel.org/r/162391825688.1173366.3437507255136307904.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v2

Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>