Re: [dpdk-dev] [PATCH v2] rte_mempool_dump() crashes with NULL rte_mempool pointer.

[Neil Horman <nhorman@tuxdriver.com>]

On Thu, Oct 02, 2014 at 09:47:19AM +0200, Thomas Monjalon wrote:
> 2014-10-01 17:05, Bruce Richardson:
> > On Wed, Oct 01, 2014 at 12:01:10PM -0400, Neil Horman wrote:
> > > On Wed, Oct 01, 2014 at 04:43:10PM +0100, Bruce Richardson wrote:
> > > > On Wed, Oct 01, 2014 at 11:02:27AM -0400, Neil Horman wrote:
> > > > > On Wed, Oct 01, 2014 at 03:36:45PM +0200, Thomas Monjalon wrote:
> > > > > > 2014-09-28 08:27, Neil Horman:
> > > > > > > On Sun, Sep 28, 2014 at 05:28:44AM +0000, Wiles, Roger Keith wrote:
> > > > > > > > Check the FILE *f and rte_mempool *mp pointers for NULL and
> > > > > > > > return plus print out a message if RTE_LIBRTE_MEMPOOL_DEBUG is enabled.
> > > > > > > > 
> > > > > > > > Signed-off-by: Keith Wiles <keith.wiles@windriver.com>
> > > > > > > 
> > > > > > > I'm fine with this, as I think passing in a NULL mempool is clearly a bug here,
> > > > > > > thats worth panicing over, though I wouldnt mind if we did a RTE_VERIFY_WARN
> > > > > > > macro here instead using what I suggested in my other note
> > > > > > 
> > > > > > Passing a NULL mempool to rte_mempool_dump() is a bug in the application.
> > > > > > If you look elsewhere in the DPDK code, you'll see that it's not common to do
> > > > > > such check on input parameters.
> > > > > > A similar discussion already happened few months ago:
> > > > > > 	http://dpdk.org/ml/archives/dev/2014-June/003900.html
> > > > > > 
> > > > > Not sure what your point is here Thomas.  I think we're all in agreement that
> > > > > NULL is a bad value to pass in here.  Are you asserting that we shouldn't bother
> > > > > with a NULL check at all and just accept the crash as it is?
> > > > >
> > > > 
> > > > In the general case:
> > > > * Code in the datapath should not have things like NULL checks
> > > > * However, datapath code should generally have a debug option which turns 
> > > >   these checks on to help debugging if needed. 
> > > > * Code not in the datapath probably should have these checks.
> > > > 
> > > Ok, I can understand that, but I would hope that rte_mempool_dump isn't in the
> > > datapath, its rather by definition a debug function, isn't it?
> > > Neil
> > 
> > Yes, agreed.  [So it probably should have the NULL check].
> 
> I have many arguments to not do this check:
> 1) If it was a coding rule to do this kind of check, it should be done in
> almost every functions.
Only if NULL is an invalid value, and we spot check for NULL all the time (see
eal_parse_coremask as an example from a quick search).

> 2) It's quite common to not do this check, e.g. what happen with memcpy(NULL,NULL)?
Its also quite common to do the check.  I think this is more about if it makes
sense to do it here (i.e. is it a common error to pass a NULL pointer into
mempool_dump?).  If so, an extra check with its own specific panic might be
nice.

> 3) Why check only NULL value? 1 and 2 are also some invalid values...
> 
Because NULL is the common case.
Neil

> -- 
> Thomas
>