Re: [PATCH 2/2] iommu/vt-d: Use BUG_ON to check NULL value of 'table'

[Yanfei Xu]

Hi Baolu,

On 5/31/2023 11:26 AM, Baolu Lu wrote:
> On 5/30/23 5:25 PM, Yanfei Xu wrote:
> > Checking NULL value of 'table' variable deserves a BUG_ON as the
> > following code will trigger a crash by dereferencing the NULL
> > 'table' pointer. Crash in advance with BUG_ON to avoid WARN_ON
> > plus NULL pointer dereferencing can simplify the crash log.
> >
> > Signed-off-by: Yanfei Xu<yanfei.xu@xxxxxxxxx>
> > ---
> >   drivers/iommu/intel/iommu.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index e98f1b122b49..8aa3bfdb7f95 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -1944,7 +1944,7 @@ static int domain_context_mapping_one(struct 
> > dmar_domain *domain,
> >       if (sm_supported(iommu)) {
> >           unsigned long pds;
> >   -        WARN_ON(!table);
> > +        BUG_ON(!table);
>
> BUG_ON() is not recommended. Perhaps,
>
>         if (!table)
>             -ENODEV;
Agree:) It is always better to handle the error than crash kernel.

How about:
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 8096273b034c..7f077e3a4128 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -1944,7 +1944,10 @@ static int domain_context_mapping_one(struct 
dmar_domain *domain,
        if (sm_supported(iommu)) {
                unsigned long pds;

-               WARN_ON(!table);
+               if (WARN_ON(!table)) {
+                       ret = -ENODEV;
+                       goto out_unlock;
+               }

Thanks,
Yanfei

> ?
>
> Best regards,
> baolu