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    Subject[PATCH 5.9 451/757] powerpc/papr_scm: Fix warning triggered by perf_stats_show()
    Date
    From: Vaibhav Jain <vaibhav@linux.ibm.com>

    [ Upstream commit ca78ef2f08ccfa29b711d644964cdf9d7ace15e5 ]

    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: 2d02bf835e57 ("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>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/20200912081451.66225-1-vaibhav@linux.ibm.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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);

    --
    2.25.1


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