linux-kernel - Re: [PATCH v3 1/2] afs: Fix afs_write

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Message-ID: <YNC3vP4BKi5l6SfW@casper.infradead.org>
Date:   Mon, 21 Jun 2021 17:01:00 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-cachefs@...hat.com, linux-afs@...ts.infradead.org,
        Jeff Layton <jlayton@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] afs: Fix afs_write_end() to handle short writes

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@...nel.org>
> Signed-off-by: David Howells <dhowells@...hat.com>
> Acked-by: Jeff Layton <jlayton@...nel.org>
> cc: Al Viro <viro@...iv.linux.org.uk>
> cc: Matthew Wilcox <willy@...radead.org>
> cc: linux-afs@...ts.infradead.org
> Link: https://lore.kernel.org/r/YMwVp268KTzTf8cN@zeniv-ca.linux.org.uk/ [1]
> Link: https://lore.kernel.org/r/162367682522.460125.5652091227576721609.stgit@warthog.procyon.org.uk/ # v1
> Link: https://lore.kernel.org/r/162391825688.1173366.3437507255136307904.stgit@warthog.procyon.org.uk/ # v2

Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>