[lustre-devel] [PATCH v2] staging/lustre/ptlrpc: Removes potential null dereference

Lidza Louina lidza.louina at oracle.com
Tue May 17 14:22:20 UTC 2016

On 05/17/2016 02:53 AM, Dan Carpenter wrote:
> When I read the code, I just assumed desc was a pointer and it should
> have been:
> 	if (!desc)
> 		return NULL;
> For me, "if (rc) " is way more readable than "if (rc != 0) ".  So
> readability could go either way depending on what you're used to, I
> suppose.
> It should definitely == 0 and != 0 if you are talking about the actual
> number zero instead of success/fail like we are here.  Also it helps to
> use == 0 with strcmp() and friends (although half of the kernel does not
> know that trick yet).
> The other thing which I have noticed recently is that a lot of
> subsystems use a mix of "if (rc) " and "if (rc < 0) ".  It's annoying
> for Smatch because say a function only returns zero but the some of the
> callers check for < 0 and some check for != 0.  We can't know for sure
> that they are equivalent.
> regards,
> dan carpenter

Hey Dan,

if (rc < 0) and if (rc) pretty much translates to the same thing. It'll 
only return a negative error value if there are problems and 0 if it 
succeeds. I feel like the first way is more explicit, since negative 
numbers are usually used for errors. I've sent a 3rd version of the 
patch with (rc < 0).

And I'm not sure about the way other subsystems use return values. Here 
it should only either be less than or equal to 0 so it makes sense to  
me in this circumstance.

I ran smatch on my patched file `../smatch/smatch_scripts/kchecker 
drivers/staging/lustre/lustre/ptlrpc/sec_plain.c` and it didn't find any 
issues with it.


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