linux-kernel - Re: [PATCH] fs/eventpoll: error handling micro-cleanup

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Date:	Sun, 01 Oct 2006 12:30:20 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Davide Libenzi <davidel@...ilserver.org>
CC:	Andrew Morton <akpm@...l.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs/eventpoll: error handling micro-cleanup

Davide Libenzi wrote:
> On Sun, 1 Oct 2006, Jeff Garzik wrote:
> 
>> Davide Libenzi wrote:
>>> On Sun, 1 Oct 2006, Jeff Garzik wrote:
>>>
>>>> While reviewing the 'may be used uninitialized' bogus gcc warnings,
>>>> I noticed that an error code assignment was only needed if an error had
>>>> actually occured.
>>> But that saved one line of code, and there are countless occurences in the
>>> kernel of such code pattern ;)
>> I'm not sure there are countless occurrences with PTR_ERR().  The line is
>> incorrect (but harmless) if inode is a valid pointer...
> 
> I just tried a `find /usr/src/linux-2.6.16/ -type f -exec grep -H -C 2 PTR_ERR {} \;`
> and looked at the cases where the error variable is assigned in any case 
> before the test. Same code pattern as, like:
> 
> error = -EFAULT;
> if (copy_from_user(...))
> 	goto kaboom;

No, that's quite different.  I'm talking about

	ptr = get_a_pointer_from_somewhere()
	error = PTR_ERR(ptr)

See the difference?  The error variable is directly assigned from a 
potentially-valid pointer.  Doing that is quite error prone, whereas
	error = -EFOO
is not.

	Jeff


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