From: Tom Zanussi tom.zanussi@linux.intel.com

Because there may be random garbage beyond a string's null terminator, it's not correct to copy the the complete character array for use as a hist trigger key. This results in multiple histogram entries for the 'same' string key.

So, in the case of a string key, use strncpy instead of memcpy to avoid copying in the extra bytes.

Before, using the gdbus entries in the following hist trigger as an example:

# echo 'hist:key=comm' > /sys/kernel/debug/tracing/events/sched/sched_waking/trigger # cat /sys/kernel/debug/tracing/events/sched/sched_waking/hist

...

{ comm: ImgDecoder #4 } hitcount: 203 { comm: gmain } hitcount: 213 { comm: gmain } hitcount: 216 { comm: StreamTrans #73 } hitcount: 221 { comm: mozStorage #3 } hitcount: 230 { comm: gdbus } hitcount: 233 { comm: StyleThread#5 } hitcount: 253 { comm: gdbus } hitcount: 256 { comm: gdbus } hitcount: 260 { comm: StyleThread#4 } hitcount: 271

...

# cat /sys/kernel/debug/tracing/events/sched/sched_waking/hist | egrep gdbus | wc -l 51

After:

# cat /sys/kernel/debug/tracing/events/sched/sched_waking/hist | egrep gdbus | wc -l 1

Link: http://lkml.kernel.org/r/50c35ae1267d64eee975b8125e151e600071d4dc.1549309756...

Cc: Namhyung Kim namhyung@kernel.org Cc: stable@vger.kernel.org Fixes: 79e577cbce4c4 ("tracing: Support string type key properly") Signed-off-by: Tom Zanussi tom.zanussi@linux.intel.com Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org --- kernel/trace/trace_events_hist.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index 5b03b9a869bb..c7774fa119a7 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -5157,9 +5157,10 @@ static inline void add_to_key(char *compound_key, void *key, /* ensure NULL-termination */ if (size > key_field->size - 1) size = key_field->size - 1; - }

- memcpy(compound_key + key_field->offset, key, size); + strncpy(compound_key + key_field->offset, (char *)key, size); + } else + memcpy(compound_key + key_field->offset, key, size); }

static void