Re: [PATCH][RESEND] Semi-pointless NULL test in uli526x driver

[Jeff Garzik <jeff@garzik.org>]

Jesper Juhl wrote:
> On 07/08/07, Jeff Garzik <jeff@garzik.org> wrote:
> > Jesper Juhl wrote:
> > > (resending previously submitted patch from 16/7-2007 22:40)
> > >
> > >
> > > Hi,
> > >
> > > In drivers/net/tulip/uli526x.c::uli526x_interrupt() there's a test
> > > of the function argument 'void *dev_id' against NULL. But that
> > > test is pretty pointless, since if ever 'dev_id' is NULL we'll
> > > already have crashed inside "netdev_priv(dev)".
> > >
> > > I don't think dev_id can ever actually be NULL, so the whole block
> > > inside "if (!dev) {" could probably just go away. But I guess
> > > there's a good reason someone put that ULI526X_DBUG() in there - and
> > > if 'dev_id' /can/ actually be NULL then it's nice to have and in
> > > that case this patch actually fixes a possible crash (hence the
> > > version number update).
> > > So I guess that in this case we should just move the
> > > "db = netdev_priv(dev)" assignment past that NULL test. That's what
> > > this patch does.
> > >
> > > Found by the Coverity checker.
> > > Compile tested.
> > >
> > >
> > > PS. Please keep me on Cc when replying.
> > >
> > >
> > > Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
> > Just remove the dev==NULL test...
>
> Hmm, it would seem there's some disagreement about that :
>
> On 04/08/07, Kyle McMartin <kyle@mcmartin.ca> wrote:
> ...
> > It *can* be null, in the case of another handler being registered on the
> > same irq number, passing NULL for the cookie.
> >
> > Ack. Will apply.
> >
> > Regards,
> >         Kyle
>
> I'll let you and Kyle fight it out :-)


My official opinion (for net drivers and ATA at least):  It is pointless 
having such a check in the hottest of driver hot paths, since a large 
majority of drivers do not have such a check.

It is better to fix the extremely rare oddball that passes NULL to 
request_irq(), than to update all drivers to be slower due to the oddballs.

	Jeff


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