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Date: Wed, 28 Mar 2007 13:14:54 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Jiri Kosina <jikos@jikos.cz>
Cc: Lee Revell <rlrevell@joe-job.com>,
       Toralf =?ISO-8859-1?Q?F=F6rster?= <toralf.foerster@gmx.de>,
       andrea@suse.de, viro@zeniv.linux.org.uk, linux-kernel@vger.kernel.org
Subject: Re: fs/block_dev.c:953: warning: 'found' might be used
 uninitialized in this function
Message-Id: <20070328131454.cdb06bc3.akpm@linux-foundation.org>
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On Wed, 28 Mar 2007 19:23:32 +0200 (CEST)
Jiri Kosina <jikos@jikos.cz> wrote:

> blockdev: bd_claim_by_kobject() could check value of unititalized pointer
> 
> Fixes this warning:
> 
> fs/block_dev.c: In function `bd_claim_by_kobject':
> fs/block_dev.c:953: warning: 'found' might be used uninitialized in this function
> 
> struct bd_holder *found is initialized only when bd_claim() returns zero. If it
> returns nonzero, ptr stays uninitialized. Later the value of the pointer is checked.
> 
> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
> 
> diff --git a/drivers/usb/input/hid-tmff.c b/drivers/usb/input/hid-tmff.c
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 575076c..e87d84a 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -950,7 +950,7 @@ static int bd_claim_by_kobject(struct block_device *bdev, void *holder,
>  				struct kobject *kobj)
>  {
>  	int res;
> -	struct bd_holder *bo, *found;
> +	struct bd_holder *bo, *found = NULL;

that generates extra code and people get upset.

One approach which we could ue in here is

	struct bd_holder *found = found;  /* Suppress bogus gcc warning */

which (surprisingly) gcc will currently accept, and which shouldn't
generate more code, although I haven't verified this.


But it's all rather ad-hoc and unpleasant.  I tend to think that we should
come up with some standardised way of squashing this warning - something
which stands out when one is reading the code, like

	struct bd_holder *found;

	squash_bogus_uninit_warning(found);	/* useful comment goes here */

which is also unpleasant, but not as unpleasant as a screenful of warnings
which hide real problems, IMO.