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From: Yanfei Xu <yanfei.xu@intel.com>
To: dwmw2@infradead.org, baolu.lu@linux.intel.com, joro@8bytes.org,
will@kernel.org, robin.murphy@arm.com
Cc: iommu@lists.linux.dev, linux-kernel@vger.kernel.org,
yanfei.xu@intel.com
Subject: [PATCH 2/2] iommu/vt-d: Use BUG_ON to check NULL value of 'table'
Date: Tue, 30 May 2023 17:25:03 +0800
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|
| Series |
Misc cleanup for iommu/vt-d
|
|
Commit Message
Yanfei Xu
May 30, 2023, 9:25 a.m. UTC
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(-)
Comments
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; ? Best regards, baolu
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@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; > 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
On 5/31/23 3:09 PM, Yanfei Xu wrote: > 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@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; >> > 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; > + } I'd recommend to remove this line directly. This pointer will be accessed in the following code, if empty "table" really happens, the kernel will report a NULL pointer reference warning at the first place. In the same function, I also saw "WARN_ON(did == 0);". It's unnecessary as domain_id_iommu() will never return 0. Perhaps we can clean it up as well. Best regards, baolu
On 6/1/2023 9:23 AM, Baolu Lu wrote: > On 5/31/23 3:09 PM, Yanfei Xu wrote: >> 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@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; >>> >> 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; >> + } > > I'd recommend to remove this line directly. This pointer will be > accessed in the following code, if empty "table" really happens, the > kernel will report a NULL pointer reference warning at the first place. > > In the same function, I also saw "WARN_ON(did == 0);". It's unnecessary > as domain_id_iommu() will never return 0. Perhaps we can clean it up as > well. Will do in V2. Thanks, Yanfei > > Best regards, > baolu
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
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); /* Setup the PASID DIR pointer: */ pds = context_get_sm_pds(table);