Re: [PATCH v3 1/2] iommu/arm-smmu-v3: Print better events records

[Nicolin Chen <nicolinc@nvidia.com>]

On Wed, Oct 02, 2024 at 10:57:28AM -0300, Jason Gunthorpe wrote:
> On Mon, Sep 30, 2024 at 12:15:10PM -0700, Nicolin Chen wrote:
> > > +static void arm_smmu_get_evt_info(struct arm_smmu_device *smmu, u64 *evt,
> > > +                                 struct arm_smmu_event *event)
> > > +{
> > > +       mutex_lock(&smmu->streams_mutex);
> > > +       event->master = arm_smmu_find_master(smmu, event->sid);
> > > +       mutex_unlock(&smmu->streams_mutex);
> > > +
> > > +       if (event->master)
> > > +               event->master_name = dev_name(event->master->dev);
> > > +       else
> > > +               event->master_name = "(unassigned sid)";
> >
> > Likely safer for dev_name to be in the mutex too.
> 
> The result of arm_smmu_find_master() should not leave the lock, and

Yea, "master_name = dev_name()" must be locked. Yet..

> dev_name()'s result can't leave the lock either, at least not with out
> some refcounting on the struct device.

I found dev_name returns "const char *" so the string source is
likely in the data section? If so, could the result of a locked
"master_name = dev_name()" get away from the lock?

Thanks
Nicolin