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

From: Jeff Garzik
Date: Tue Aug 07 2007 - 17:55:06 EST


Jesper Juhl wrote:
On 07/08/07, Jeff Garzik <jeff@xxxxxxxxxx> 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@xxxxxxxxx>
Just remove the dev==NULL test...


Hmm, it would seem there's some disagreement about that :

On 04/08/07, Kyle McMartin <kyle@xxxxxxxxxxx> 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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