linux-kernel - Re: [PATCH RFC netfs] Fix uninitialized variable in netfs_retry_read

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Message-ID: <03561ca5-df13-4b6c-8ac8-2dfe45ec2b6d@paulmck-laptop>
Date: Thu, 19 Dec 2024 17:07:17 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: David Howells <dhowells@...hat.com>
Cc: Christian Brauner <brauner@...nel.org>, jlayton@...nel.org,
	netfs@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, sfr@...b.auug.org.au,
	linux-next@...r.kernel.org
Subject: Re: [PATCH RFC netfs] Fix uninitialized variable in
 netfs_retry_read_subrequests()

On Fri, Dec 20, 2024 at 12:20:11AM +0000, David Howells wrote:
> Paul E. McKenney <paulmck@...nel.org> wrote:
> 
> > This should actually be considered more of a bug report than a patch.
> > 
> > Clang 18.1.8 (but not GCC 11.5.0) complains that the "subreq" local
> > variable can be used uninitialized in netfs_retry_read_subrequests(),
> > just after the abandon_after label.  This function is unusual in having
> > three instances of this local variable.  The third and last one is clearly
> > erroneous because there is a branch out of the enclosing do-while loop
> > to the end of this function, and it looks like the intent is that the
> > code at the end of this function be using the same value of the "subreq"
> > local variable as is used within that do-while loop.
> > 
> > Therefore, take the obvious (if potentially quite misguided) approach
> > of removing the third declaration of "subreq", instead simply setting
> > it to NULL.
> 
> I think you're looking at the old version of my netfs-writeback branch that's
> residing in Christian's vfs.netfs branch.  I've posted a new version of my
> branch[1] without this problem and am hoping for Christian to update the
> branch[2] so that Stephen can pull it into linux-next.

Me too, and thank you for looking into this!

							Thanx, Paul

> David
> 
> [1] https://lore.kernel.org/linux-fsdevel/20241216204124.3752367-1-dhowells@redhat.com/T/#t
> 
> [2] And hoping he'll remember to drop "[PATCH v5 26/32] Display waited-on page
> index after 1min of waiting" for me.  I forgot to remove that debugging patch.
>