Re: [PATCH 3/5] coresight: Fix csdev connections initialisation

[Suzuki K Poulose]

On 31/05/16 18:55, Mathieu Poirier wrote:
> On 31 May 2016 at 05:57, Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote:
> > This is a cleanup patch.
> >
> > coresight_device->conns holds an array to point to the devices
> > connected to the OUT ports of a component. Sinks, e.g ETR, do not
> > have an OUT port (nr_outport = 0), as it streams the trace to
> > memory via AXI.
> >
> > At coresight_register() we do :
> >
> >          conns = kcalloc(csdev->nr_outport, sizeof(*conns), GFP_KERNEL);
> >          if (!conns) {
> >                  ret = -ENOMEM;
> >                  goto err_kzalloc_conns;
> >          }
> >
> > For ETR, since the total size requested for kcalloc is zero, the return value is,
> > ZERO_SIZE_PTR ( != NULL). Hence, csdev->conns = ZERO_SIZE_PTR which cannot be
> > verified later to contain a valid pointer. The code which accesses the csdev->conns
> > is bounded by the csdev->nr_outport check, hence we don't try to dereference the
> > ZERO_SIZE_PTR. This patch cleans up the csdev->conns and csdev->refcnt, initialisation
> > to make sure we initialise it properly(i.e, either NULL or valid conns array).
> >
> > Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > ---
> >   drivers/hwtracing/coresight/coresight.c | 42 +++++++++++++++++++--------------
> >   1 file changed, 24 insertions(+), 18 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight.c b/drivers/hwtracing/coresight/coresight.c
> > index 0fdaaf4..8410420 100644
> > --- a/drivers/hwtracing/coresight/coresight.c
> > +++ b/drivers/hwtracing/coresight/coresight.c
> > @@ -890,7 +890,7 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
> >          int nr_refcnts = 1;
> >          atomic_t *refcnts = NULL;
> >          struct coresight_device *csdev;
> > -       struct coresight_connection *conns;
> > +       struct coresight_connection *conns = NULL;
> >
> >          csdev = kzalloc(sizeof(*csdev), GFP_KERNEL);
> >          if (!csdev) {
> > @@ -908,29 +908,35 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
> >                          nr_refcnts = desc->pdata->nr_outport;
> >          }
> >
> > -       refcnts = kcalloc(nr_refcnts, sizeof(*refcnts), GFP_KERNEL);
> > -       if (!refcnts) {
> > -               ret = -ENOMEM;
> > -               goto err_kzalloc_refcnts;
> > -       }
> > +       if (nr_refcnts) {
>
> Did you manage to find a usecase where "nr_refcnts == 0" ?  Since
> components have at least one port this condition will always be true.

No, I didn't find one. While I was fixing the nr_outport, I thought it would
be good to check the refcnts as well.

> > -       csdev->conns = conns;
> > +               for (i = 0; i < csdev->nr_outport; i++) {
> > +                       conns[i].outport = desc->pdata->outports[i];
> > +                       conns[i].child_name = desc->pdata->child_names[i];
> > +                       conns[i].child_port = desc->pdata->child_ports[i];
> > +               }
> > +
> > +               csdev->conns = conns;
>
> The purpose of your patch is to correctly initialise csdev->conns to
> NULL if there is no output port to speak of.  As such shouldn't the
> above statement be out of the if (csdev->nr_outport) {} ?.

Not necessarily. We do a kzalloc() for csdev, which implies csdev->conns
is already NULL. I can move the code to make that explicit assignment.

> I'm also getting a couple of checkpatch.pl warnings on this patch.

I can fix those warnings. I ignored them initially, as it was for the length of the comment.

Cheers
Suzuki