[PATCH v2] powerpc/papr_scm: Fix warning triggered by perf_stats_show()

[PATCH v2] powerpc/papr_scm: Fix warning triggered by perf_stats_show()

[Vaibhav Jain]

A warning is reported by the kernel in case perf_stats_show() returns
an error code. The warning is of the form below:

 papr_scm ibm,persistent-memory:ibm,pmemory@44100001:
 	  Failed to query performance stats, Err:-10
 dev_attr_show: perf_stats_show+0x0/0x1c0 [papr_scm] returned bad count
 fill_read_buffer: dev_attr_show+0x0/0xb0 returned bad count

On investigation it looks like that the compiler is silently truncating the
return value of drc_pmem_query_stats() from 'long' to 'int', since the
variable used to store the return code 'rc' is an 'int'. This
truncated value is then returned back as a 'ssize_t' back from
perf_stats_show() to 'dev_attr_show()' which thinks of it as a large
unsigned number and triggers this warning..

To fix this we update the type of variable 'rc' from 'int' to
'ssize_t' that prevents the compiler from truncating the return value
of drc_pmem_query_stats() and returning correct signed value back from
perf_stats_show().

Fixes: 2d02bf835e573 ('powerpc/papr_scm: Fetch nvdimm performance
       stats from PHYP')
Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
---
Changelog:

v2: Added an explicit cast to the expression calling 'seq_buf_used()'
    and triggering this issue. [ Ira ]
---
 arch/powerpc/platforms/pseries/papr_scm.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
index a88a707a608aa..5493bc847bd08 100644
--- a/arch/powerpc/platforms/pseries/papr_scm.c
+++ b/arch/powerpc/platforms/pseries/papr_scm.c
@@ -785,7 +785,8 @@ static int papr_scm_ndctl(struct nvdimm_bus_descriptor *nd_desc,
 static ssize_t perf_stats_show(struct device *dev,
 			       struct device_attribute *attr, char *buf)
 {
-	int index, rc;
+	int index;
+	ssize_t rc;
 	struct seq_buf s;
 	struct papr_scm_perf_stat *stat;
 	struct papr_scm_perf_stats *stats;
@@ -820,7 +821,7 @@ static ssize_t perf_stats_show(struct device *dev,
 
 free_stats:
 	kfree(stats);
-	return rc ? rc : seq_buf_used(&s);
+	return rc ? rc : (ssize_t)seq_buf_used(&s);
 }
 DEVICE_ATTR_ADMIN_RO(perf_stats);
 
-- 
2.26.2

Re: [PATCH v2] powerpc/papr_scm: Fix warning triggered by perf_stats_show()

[Ira Weiny]

On Sat, Sep 12, 2020 at 01:44:51PM +0530, Vaibhav Jain wrote:
> A warning is reported by the kernel in case perf_stats_show() returns
> an error code. The warning is of the form below:
> 
>  papr_scm ibm,persistent-memory:ibm,pmemory@44100001:
>  	  Failed to query performance stats, Err:-10
>  dev_attr_show: perf_stats_show+0x0/0x1c0 [papr_scm] returned bad count
>  fill_read_buffer: dev_attr_show+0x0/0xb0 returned bad count
> 
> On investigation it looks like that the compiler is silently truncating the
> return value of drc_pmem_query_stats() from 'long' to 'int', since the
> variable used to store the return code 'rc' is an 'int'. This
> truncated value is then returned back as a 'ssize_t' back from
> perf_stats_show() to 'dev_attr_show()' which thinks of it as a large
> unsigned number and triggers this warning..
> 
> To fix this we update the type of variable 'rc' from 'int' to
> 'ssize_t' that prevents the compiler from truncating the return value
> of drc_pmem_query_stats() and returning correct signed value back from
> perf_stats_show().
> 
> Fixes: 2d02bf835e573 ('powerpc/papr_scm: Fetch nvdimm performance
>        stats from PHYP')
> Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>

Reviewed-by: Ira Weiny <ira.weiny@intel.com>

> ---
> Changelog:
> 
> v2: Added an explicit cast to the expression calling 'seq_buf_used()'
>     and triggering this issue. [ Ira ]
> ---
>  arch/powerpc/platforms/pseries/papr_scm.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> index a88a707a608aa..5493bc847bd08 100644
> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> @@ -785,7 +785,8 @@ static int papr_scm_ndctl(struct nvdimm_bus_descriptor *nd_desc,
>  static ssize_t perf_stats_show(struct device *dev,
>  			       struct device_attribute *attr, char *buf)
>  {
> -	int index, rc;
> +	int index;
> +	ssize_t rc;
>  	struct seq_buf s;
>  	struct papr_scm_perf_stat *stat;
>  	struct papr_scm_perf_stats *stats;
> @@ -820,7 +821,7 @@ static ssize_t perf_stats_show(struct device *dev,
>  
>  free_stats:
>  	kfree(stats);
> -	return rc ? rc : seq_buf_used(&s);
> +	return rc ? rc : (ssize_t)seq_buf_used(&s);
>  }
>  DEVICE_ATTR_ADMIN_RO(perf_stats);
>  
> -- 
> 2.26.2
> 

Re: [PATCH v2] powerpc/papr_scm: Fix warning triggered by perf_stats_show()

[Michael Ellerman]

Vaibhav Jain <vaibhav@linux.ibm.com> writes:
> A warning is reported by the kernel in case perf_stats_show() returns
> an error code. The warning is of the form below:
>
>  papr_scm ibm,persistent-memory:ibm,pmemory@44100001:
>  	  Failed to query performance stats, Err:-10
>  dev_attr_show: perf_stats_show+0x0/0x1c0 [papr_scm] returned bad count
>  fill_read_buffer: dev_attr_show+0x0/0xb0 returned bad count
>
> On investigation it looks like that the compiler is silently truncating the
> return value of drc_pmem_query_stats() from 'long' to 'int', since the
> variable used to store the return code 'rc' is an 'int'. This
> truncated value is then returned back as a 'ssize_t' back from
> perf_stats_show() to 'dev_attr_show()' which thinks of it as a large
> unsigned number and triggers this warning..
>
> To fix this we update the type of variable 'rc' from 'int' to
> 'ssize_t' that prevents the compiler from truncating the return value
> of drc_pmem_query_stats() and returning correct signed value back from
> perf_stats_show().
>
> Fixes: 2d02bf835e573 ('powerpc/papr_scm: Fetch nvdimm performance
>        stats from PHYP')

Please don't word wrap the Fixes tag it breaks b4.

I've fixed it up this time.

cheers

Re: [PATCH v2] powerpc/papr_scm: Fix warning triggered by perf_stats_show()

[Vaibhav Jain]

Michael Ellerman <mpe@ellerman.id.au> writes:

> Vaibhav Jain <vaibhav@linux.ibm.com> writes:
>> A warning is reported by the kernel in case perf_stats_show() returns
>> an error code. The warning is of the form below:
>>
>>  papr_scm ibm,persistent-memory:ibm,pmemory@44100001:
>>  	  Failed to query performance stats, Err:-10
>>  dev_attr_show: perf_stats_show+0x0/0x1c0 [papr_scm] returned bad count
>>  fill_read_buffer: dev_attr_show+0x0/0xb0 returned bad count
>>
>> On investigation it looks like that the compiler is silently truncating the
>> return value of drc_pmem_query_stats() from 'long' to 'int', since the
>> variable used to store the return code 'rc' is an 'int'. This
>> truncated value is then returned back as a 'ssize_t' back from
>> perf_stats_show() to 'dev_attr_show()' which thinks of it as a large
>> unsigned number and triggers this warning..
>>
>> To fix this we update the type of variable 'rc' from 'int' to
>> 'ssize_t' that prevents the compiler from truncating the return value
>> of drc_pmem_query_stats() and returning correct signed value back from
>> perf_stats_show().
>>
>> Fixes: 2d02bf835e573 ('powerpc/papr_scm: Fetch nvdimm performance
>>        stats from PHYP')
>
> Please don't word wrap the Fixes tag it breaks b4.
>
> I've fixed it up this time.

Thanks Mpe

>
> cheers

-- 
Cheers
~ Vaibhav

Re: [PATCH v2] powerpc/papr_scm: Fix warning triggered by perf_stats_show()

[Michael Ellerman]

On Sat, 12 Sep 2020 13:44:51 +0530, Vaibhav Jain wrote:
> A warning is reported by the kernel in case perf_stats_show() returns
> an error code. The warning is of the form below:
> 
>  papr_scm ibm,persistent-memory:ibm,pmemory@44100001:
>  	  Failed to query performance stats, Err:-10
>  dev_attr_show: perf_stats_show+0x0/0x1c0 [papr_scm] returned bad count
>  fill_read_buffer: dev_attr_show+0x0/0xb0 returned bad count
> 
> [...]

Applied to powerpc/next.

[1/1] powerpc/papr_scm: Fix warning triggered by perf_stats_show()
      https://git.kernel.org/powerpc/c/ca78ef2f08ccfa29b711d644964cdf9d7ace15e5

cheers