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 <vaib...@linux.ibm.com>
Reviewed-by: Ira Weiny <ira.we...@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
>
