[PATCH 0/2] A couple hist trigger patches

[PATCH 0/2] A couple hist trigger patches

[Tom Zanussi]

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

Hi,

Here are a couple miscellaneous hist trigger patches which can be
applied independently of the onchange/snapshot patches.

The first is just an additional use of str_has_prefix() that was
apparently missed in the original str_has_prefix() conversion, with an
update suggested by Joe Perches.

The second fixes a bug I noticed when testing the onchange/snapshot
fixes.

I pulled these out into this separate patchset because they should be
applied regardless of what happens with the onchange/snapshot patchset.

Thanks,

Tom


The following changes since commit 67748dbeaf2b1240c0b87588df4bb0fb9471a751:

  sh: ftrace: Fix missing parenthesis in WARN_ON() (2019-01-08 10:19:02 -0600)

are available in the git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/zanussi/linux-trace.git ftrace/hist-fixes-v1

Tom Zanussi (2):
  tracing: Use str_has_prefix() in synth_event_create()
  tracing: Use strncpy instead of memcpy for string keys in hist
    triggers

 kernel/trace/trace_events_hist.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

-- 
2.14.1

[PATCH 1/2] tracing: Use str_has_prefix() in synth_event_create()

[Tom Zanussi]

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

Since we now have a str_has_prefix() that returns the length, we can
use that instead of explicitly calculating it.

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Cc: Joe Perches <joe@perches.com>
---
 kernel/trace/trace_events_hist.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 449d90cfa151..c4a667503bf0 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1200,8 +1200,8 @@ static int synth_event_create(int argc, const char **argv)
 
 	/* This interface accepts group name prefix */
 	if (strchr(name, '/')) {
-		len = sizeof(SYNTH_SYSTEM "/") - 1;
-		if (strncmp(name, SYNTH_SYSTEM "/", len))
+		len = str_has_prefix(name, SYNTH_SYSTEM "/");
+		if (len == 0)
 			return -EINVAL;
 		name += len;
 	}
-- 
2.14.1

[PATCH 2/2] tracing: Use strncpy instead of memcpy for string keys in hist triggers

[Tom Zanussi]

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);
 }
 
 static void
-- 
2.14.1

Re: [PATCH 0/2] A couple hist trigger patches

[Tom Zanussi]

Ping...

On Mon, 2019-02-04 at 15:07 -0600, Tom Zanussi wrote:
> From: Tom Zanussi <tom.zanussi@linux.intel.com>
> 
> Hi,
> 
> Here are a couple miscellaneous hist trigger patches which can be
> applied independently of the onchange/snapshot patches.
> 
> The first is just an additional use of str_has_prefix() that was
> apparently missed in the original str_has_prefix() conversion, with
> an
> update suggested by Joe Perches.
> 
> The second fixes a bug I noticed when testing the onchange/snapshot
> fixes.
> 
> I pulled these out into this separate patchset because they should be
> applied regardless of what happens with the onchange/snapshot
> patchset.
> 
> Thanks,
> 
> Tom
> 
> 
> The following changes since commit
> 67748dbeaf2b1240c0b87588df4bb0fb9471a751:
> 
>   sh: ftrace: Fix missing parenthesis in WARN_ON() (2019-01-08
> 10:19:02 -0600)
> 
> are available in the git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/zanussi/linux-
> trace.git ftrace/hist-fixes-v1
> 
> Tom Zanussi (2):
>   tracing: Use str_has_prefix() in synth_event_create()
>   tracing: Use strncpy instead of memcpy for string keys in hist
>     triggers
> 
>  kernel/trace/trace_events_hist.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 

Re: [PATCH 0/2] A couple hist trigger patches

[Steven Rostedt]

On Mon, 04 Mar 2019 14:11:03 -0600
Tom Zanussi <tzanussi@gmail.com> wrote:

> Ping...
> 
>

Thanks for the ping. It got buried.

-- Steve

Re: [PATCH 2/2] tracing: Use strncpy instead of memcpy for string keys in hist triggers

[Steven Rostedt]

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

Re: [PATCH 2/2] tracing: Use strncpy instead of memcpy for string keys in hist triggers

[Steven Rostedt]

On Mon, 4 Mar 2019 16:50:00 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> > +++ 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.

Note, if that is changed, it can be another patch. This one is fine as
is. I just was looking at other use cases of memcpy() in that file.

-- Steve

Re: [PATCH 2/2] tracing: Use strncpy instead of memcpy for string keys in hist triggers

[Tom Zanussi]

Hi Steve,

On Mon, 2019-03-04 at 16:56 -0500, Steven Rostedt wrote:
> On Mon, 4 Mar 2019 16:50:00 -0500
> Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> > > +++ 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.
> 
> Note, if that is changed, it can be another patch. This one is fine
> as
> is. I just was looking at other use cases of memcpy() in that file.
> 

Hmm, I don't think it's really necessary - it's not used in a key so
don't care about anything after the null, and TASK_COMM_LEN is used in
the memcpy.

Tom

> -- Steve

Re: [PATCH 2/2] tracing: Use strncpy instead of memcpy for string keys in hist triggers

[Tom Zanussi]

Hi Steve,

On Mon, 2019-03-04 at 16:22 -0600, Tom Zanussi wrote:
> Hi Steve,
> 
> On Mon, 2019-03-04 at 16:56 -0500, Steven Rostedt wrote:
> > On Mon, 4 Mar 2019 16:50:00 -0500
> > Steven Rostedt <rostedt@goodmis.org> wrote:
> > 
> > > > +++ 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.
> > 
> > Note, if that is changed, it can be another patch. This one is fine
> > as
> > is. I just was looking at other use cases of memcpy() in that file.
> > 
> 
> Hmm, I don't think it's really necessary - it's not used in a key so
> don't care about anything after the null, and TASK_COMM_LEN is used
> in
> the memcpy.

Never mind, yeah, it would make sense to do this, will create another
patch...

Tom


> 
> Tom
> 
> > -- Steve

Re: [PATCH 2/2] tracing: Use strncpy instead of memcpy for string keys in hist triggers

[Steven Rostedt]

On Mon, 04 Mar 2019 16:31:40 -0600
Tom Zanussi <tom.zanussi@linux.intel.com> wrote:

> > Hmm, I don't think it's really necessary - it's not used in a key so
> > don't care about anything after the null, and TASK_COMM_LEN is used
> > in
> > the memcpy.  
> 
> Never mind, yeah, it would make sense to do this, will create another
> patch...

And probably should change the memcpy() of comm in kernel/trace/trace.c
too. It could be that memcpy() is a little bit faster than strncpy(),
and this is done on scheduling switches when tracing is active, but
still, I'm starting to think that isn't a good choice.

-- Steve

Re: [PATCH 2/2] tracing: Use strncpy instead of memcpy for string keys in hist triggers

[Tom Zanussi]

On Mon, 2019-03-04 at 18:45 -0500, Steven Rostedt wrote:
> On Mon, 04 Mar 2019 16:31:40 -0600
> Tom Zanussi <tom.zanussi@linux.intel.com> wrote:
> 
> > > Hmm, I don't think it's really necessary - it's not used in a key
> > > so
> > > don't care about anything after the null, and TASK_COMM_LEN is
> > > used
> > > in
> > > the memcpy.  
> > 
> > Never mind, yeah, it would make sense to do this, will create
> > another
> > patch...
> 
> And probably should change the memcpy() of comm in
> kernel/trace/trace.c
> too. It could be that memcpy() is a little bit faster than strncpy(),
> and this is done on scheduling switches when tracing is active, but
> still, I'm starting to think that isn't a good choice.
> 

OK, will add that too.

Tom


> -- Steve