From: Steven Rostedt <rostedt@goodmis.org>
To: Tom Zanussi <zanussi@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org,
Tom Zanussi <tom.zanussi@linux.intel.com>,
Namhyung Kim <namhyung@kernel.org>
Subject: Re: [PATCH 2/2] tracing: Use strncpy instead of memcpy for string keys in hist triggers
Date: Mon, 4 Mar 2019 16:50:00 -0500 [thread overview]
Message-ID: <20190304165000.0ce0fbdd@gandalf.local.home> (raw)
In-Reply-To: <50c35ae1267d64eee975b8125e151e600071d4dc.1549309756.git.tom.zanussi@linux.intel.com>
On Mon, 4 Feb 2019 15:07:24 -0600
Tom Zanussi <zanussi@kernel.org> wrote:
> 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
>
> Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
> Cc: Namhyung Kim <namhyung@kernel.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 c4a667503bf0..1b349689b897 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -4695,9 +4695,10 @@ 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);
> }
>
Shouldn't we use strncpy() in save_comm() too. Feels safer.
-- Steve
next prev parent reply other threads:[~2019-03-04 21:50 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-04 21:07 [PATCH 0/2] A couple hist trigger patches Tom Zanussi
2019-02-04 21:07 ` [PATCH 1/2] tracing: Use str_has_prefix() in synth_event_create() Tom Zanussi
2019-02-04 21:07 ` [PATCH 2/2] tracing: Use strncpy instead of memcpy for string keys in hist triggers Tom Zanussi
2019-03-04 21:50 ` Steven Rostedt [this message]
2019-03-04 21:56 ` Steven Rostedt
2019-03-04 22:22 ` Tom Zanussi
2019-03-04 22:31 ` Tom Zanussi
2019-03-04 23:45 ` Steven Rostedt
2019-03-05 0:02 ` Tom Zanussi
2019-03-04 20:11 ` [PATCH 0/2] A couple hist trigger patches Tom Zanussi
2019-03-04 21:26 ` Steven Rostedt
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