linux-kernel - Re: ext4_lazyinit_thread: 'ret' may be used uninitialized in this function

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Date:	Tue, 2 Nov 2010 15:19:09 -0400 (EDT)
From:	Lukas Czerner <lczerner@...hat.com>
To:	kevin granade <kevin.granade@...il.com>
cc:	"Ted Ts'o" <tytso@....edu>, Lukas Czerner <lczerner@...hat.com>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: ext4_lazyinit_thread: 'ret' may be used uninitialized in this
 function

On Tue, 2 Nov 2010, kevin granade wrote:

> On Tue, Nov 2, 2010 at 1:29 PM, Ted Ts'o <tytso@....edu> wrote:
> >
> > On Mon, Nov 01, 2010 at 04:27:26PM +0100, Lukas Czerner wrote:
> > >
> > > thank you for noticing this, because I actually do not see the warning
> > > (I wonder why...), but it is definitely a bug, so the trivial patch below
> > > should fix that.
> >
> > This is a slightly less trivial fix that eliminates the need for the
> > "ret" variable entirely.
> >
> >                                                - Ted
> >
> > commit e048924538f0c62d18306e2fea0e22dac0140f6e
> > Author: Theodore Ts'o <tytso@....edu>
> > Date:   Tue Nov 2 14:19:30 2010 -0400
> >
> >    ext4: "ret" may be used uninitialized in ext4_lazyinit_thread()
> >
> >    Newer GCC's reported the following build warning:
> >
> >       fs/ext4/super.c: In function 'ext4_lazyinit_thread':
> >       fs/ext4/super.c:2702: warning: 'ret' may be used uninitialized in this function
> >
> >    Fix it by removing the need for the ret variable in the first place.
> >
> >    Signed-off-by: "Lukas Czerner" <lczerner@...hat.com>
> >    Reported-by: "Stefan Richter" <stefanr@...6.in-berlin.de>
> >    Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> >
> > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > index 8d1d942..4d7ef31 100644
> > --- a/fs/ext4/super.c
> > +++ b/fs/ext4/super.c
> > @@ -2699,7 +2699,6 @@ static int ext4_lazyinit_thread(void *arg)
> >        struct ext4_li_request *elr;
> >        unsigned long next_wakeup;
> >        DEFINE_WAIT(wait);
> > -       int ret;
> >
> >        BUG_ON(NULL == eli);
> >
> > @@ -2723,13 +2722,12 @@ cont_thread:
> >                        elr = list_entry(pos, struct ext4_li_request,
> >                                         lr_request);
> >
> > -                       if (time_after_eq(jiffies, elr->lr_next_sched))
> > -                               ret = ext4_run_li_request(elr);
> > -
> > -                       if (ret) {
> > -                               ret = 0;
> > -                               ext4_remove_li_request(elr);
> > -                               continue;
> > +                       if (time_after_eq(jiffies, elr->lr_next_sched)) {
> > +                               if (ext4_run_li_request(elr) != 0) {
> > +                                       /* error, remove the lazy_init job */
> > +                                       ext4_remove_li_request(elr);
> > +                                       continue;
> > +                               }
> >                        }
> >
> >                        if (time_before(elr->lr_next_sched, next_wakeup))
> 
> What do you think about this option for the second hunk? (not anything-tested)
> 
> @@ -2723,13 +2722,11 @@ cont_thread:
>                        elr = list_entry(pos, struct ext4_li_request,
>                                         lr_request);
> -                       if (time_after_eq(jiffies, elr->lr_next_sched))
> -                               ret = ext4_run_li_request(elr);
> -
> -                       if (ret) {
> -                               ret = 0;
> -                               ext4_remove_li_request(elr);
> -                               continue;
> +                       if (time_after_eq(jiffies, elr->lr_next_sched) &&
> +                           ext4_run_li_request(elr) != 0) {
> +                               /* error, remove the lazy_init job */
> +                               ext4_remove_li_request(elr);
> +                               continue;
>                        }
> 
>                        if (time_before(elr->lr_next_sched, next_wakeup))
> --
> 
> Though obviously it's a pretty subjective style issue.
> Kevin Granade

Hmm this relies on the fact that if the first part of the condition
would not be true, the second part (after and) would never be invoked,
however I am not really sure that we can rely on that on every
architecture, or can we ?

> 
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> 

Thanks!

-Lukas