Re: [PATCH v2] powerpc/papr_scm: Fix warning triggered by perf_stats_show()
From: Ira Weiny <hidden>
Date: 2020-09-14 17:00:32
Also in:
nvdimm
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 <redacted>Reviewed-by: Ira Weiny <redacted>
quoted hunk ↗ jump to hunk
--- 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