From: Jason Gunthorpe <jgg@ziepe.ca>
To: Baolu Lu <baolu.lu@linux.intel.com>
Cc: Yanfei Xu <yanfei.xu@intel.com>,
dwmw2@infradead.org, joro@8bytes.org, will@kernel.org,
robin.murphy@arm.com, iommu@lists.linux.dev,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] iommu/vt-d: Use BUG_ON to check NULL value of 'table'
Date: Fri, 2 Jun 2023 11:32:35 -0300 [thread overview]
Message-ID: <ZHn9g6QoMUo3ZPog@ziepe.ca> (raw)
In-Reply-To: <3e75f9de-4c67-93aa-9fb4-28da9849dd48@linux.intel.com>
On Wed, May 31, 2023 at 11:26:55AM +0800, 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@intel.com>
> > ---
> > 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;
>
> ?
If it is not something you think needs active debugging then just let
it crash on the NULL pointer deref. You get a nice backtrace from that
already.
The additional value of the WARN is it gives you a line number, a
prettier print and it might recover more cleanly (or not, it might
just crash somewhere else).
Jason
prev parent reply other threads:[~2023-06-02 14:32 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-30 9:25 [PATCH 0/2] Misc cleanup for iommu/vt-d Yanfei Xu
2023-05-30 9:25 ` [PATCH 1/2] iommu/vt-d: Remove the dead code in init_iommu_hw() Yanfei Xu
2023-05-31 3:24 ` Baolu Lu
2023-05-31 6:55 ` Yanfei Xu
2023-06-01 1:15 ` Baolu Lu
2023-06-01 7:49 ` Yanfei Xu
2023-05-30 9:25 ` [PATCH 2/2] iommu/vt-d: Use BUG_ON to check NULL value of 'table' Yanfei Xu
2023-05-31 3:26 ` Baolu Lu
2023-05-31 7:09 ` Yanfei Xu
2023-06-01 1:23 ` Baolu Lu
2023-06-01 4:47 ` Yanfei Xu
2023-06-02 14:32 ` Jason Gunthorpe [this message]
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