Date:   Thu, 23 Feb 2023 16:43:39 +0300
From:   Dan Carpenter <error27@gmail.com>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     trondmy@kernel.org, Anna Schumaker <Anna.Schumaker@netapp.com>,
        linux-nfs@vger.kernel.org
Subject: Re: [PATCH v2 18/18] NFS: Remove unnecessary check in
 nfs_read_folio()
Message-ID: <Y/dti5+1vp55tMZX@kadam>
References: <20230119213351.443388-11-trondmy@kernel.org>
 <20230119213351.443388-12-trondmy@kernel.org>
 <20230119213351.443388-13-trondmy@kernel.org>
 <20230119213351.443388-14-trondmy@kernel.org>
 <20230119213351.443388-15-trondmy@kernel.org>
 <20230119213351.443388-16-trondmy@kernel.org>
 <20230119213351.443388-17-trondmy@kernel.org>
 <20230119213351.443388-18-trondmy@kernel.org>
 <20230119213351.443388-19-trondmy@kernel.org>
 <Y/dorq8Elh4Mxg2g@casper.infradead.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <Y/dorq8Elh4Mxg2g@casper.infradead.org>
Precedence: bulk

On Thu, Feb 23, 2023 at 01:22:54PM +0000, Matthew Wilcox wrote:
> But I'm suspicious of static match tools claiming it can't ever happen,
> and I'd like more details please.  I can't find the original report.

I would never write a warning like that...  However at the time when
I reported the bug then Smatch did say that all the callers passed a
non-NULL file pointer.  I've reviewed my logs and that was true when I
said it but it's not true now.  :(  Now Smatch says there are three
callers and nfs_write_begin() passes a valid pointer, read_pages()
passes either a valid pointer or a NULL and filemap_read_folio() passes
an unknown pointer.

https://lore.kernel.org/all/Y77+n9MyHgx%2FalA4@kadam/

The issue here is that the pointer was already derefernced on the lines
before the check for NULL.

	struct inode *inode = file_inode(file);

So either the dereference or the check was wrong.

regards,
dan carpenter