[PATCH 0/3] kbuffer: Some minor fixes

[PATCH 0/3] kbuffer: Some minor fixes

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

The kbuffer update to work with libtracefs mmapping code had a few bugs.

1) The man page was missing its prototype for tep_kbuffer()

2) A buffer passed in to kbuffer_read_buffer() that was just big enough to
   hold the events, was not completely filled.

3) kbuffer_refresh() left the current event zero size, even if new data was
   added after it, if the last read was at the end of the page.

Steven Rostedt (Google) (3):
  libtraceevent Documentation: Fix tep_kbuffer() prototype
  kbuffer: Add event if the buffer just fits in kbuffer_read_buffer()
  kbuffer: Update kbuf->next in kbuffer_refresh()

 Documentation/libtraceevent-handle.txt |  1 +
 Documentation/libtraceevent.txt        |  2 +-
 src/kbuffer-parse.c                    | 16 +++++++++++++++-
 3 files changed, 17 insertions(+), 2 deletions(-)

-- 
2.42.0

[PATCH 1/3] libtraceevent Documentation: Fix tep_kbuffer() prototype

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

The tep_kbuffer() prototype was missing from its man page and was broken
in the libtraceevent top man page.

Link: https://lore.kernel.org/linux-trace-devel/20231229121450.7a19ccaa@gandalf.local.home

Fixes: 6e637fba207d4 ("libtraceevent: Rename kbuffer_create() to tep_kbuffer()")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 Documentation/libtraceevent-handle.txt | 1 +
 Documentation/libtraceevent.txt        | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/Documentation/libtraceevent-handle.txt b/Documentation/libtraceevent-handle.txt
index 64528ebc3433..fd55712db705 100644
--- a/Documentation/libtraceevent-handle.txt
+++ b/Documentation/libtraceevent-handle.txt
@@ -17,6 +17,7 @@ void *tep_free*(struct tep_handle pass:[*]_tep_);
 void *tep_ref*(struct tep_handle pass:[*]_tep_);
 void *tep_unref*(struct tep_handle pass:[*]_tep_);
 int *tep_get_ref*(struct tep_handle pass:[*]_tep_);
+struct kbuffer pass:[*]*tep_kbuffer*(struct tep_handle pass:[*]_tep_);
 --
 
 DESCRIPTION
diff --git a/Documentation/libtraceevent.txt b/Documentation/libtraceevent.txt
index 26e3ad2523db..9e7777283c52 100644
--- a/Documentation/libtraceevent.txt
+++ b/Documentation/libtraceevent.txt
@@ -33,7 +33,7 @@ Management of tep handler data structure and access of its members:
 	int *tep_get_header_timestamp_size*(struct tep_handle pass:[*]_tep_);
 	bool *tep_is_old_format*(struct tep_handle pass:[*]_tep_);
 	int *tep_strerror*(struct tep_handle pass:[*]_tep_, enum tep_errno _errnum_, char pass:[*]_buf_, size_t _buflen_);
-	struct kbuffer pass:[*]*tep_kbuffer*(struct tep_handle pass:[*]:_tep_);
+	struct kbuffer pass:[*]*tep_kbuffer*(struct tep_handle pass:[*]_tep_);
 
 Register / unregister APIs:
 	int *tep_register_function*(struct tep_handle pass:[*]_tep_, char pass:[*]_name_, unsigned long long _addr_, char pass:[*]_mod_);
-- 
2.42.0

[PATCH 2/3] kbuffer: Add event if the buffer just fits in kbuffer_read_buffer()

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

If the buffer passed in is exactly the size needed to add an event, it will
not because it checks with:

  while (len > kbuf->next - save_curr) {

Instead of

  while (len >= kbuf->next - save_curr) {

Fixes: 05821189 ("kbuffer: Add kbuffer_read_buffer()")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 src/kbuffer-parse.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/kbuffer-parse.c b/src/kbuffer-parse.c
index d43fe5d972fd..4801d432c58c 100644
--- a/src/kbuffer-parse.c
+++ b/src/kbuffer-parse.c
@@ -995,7 +995,7 @@ int kbuffer_read_buffer(struct kbuffer *kbuf, void *buffer, int len)
 		/* Due to timestamps, we must save the current next to use */
 		last_next = kbuf->next;
 
-		while (len > kbuf->next - save_curr) {
+		while (len >= kbuf->next - save_curr) {
 			last_next = kbuf->next;
 			if (!kbuffer_next_event(kbuf, &ts))
 				break;
-- 
2.42.0

[PATCH 3/3] kbuffer: Update kbuf->next in kbuffer_refresh()

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

If the kbuffer was read to completion, the kbuf->curr would equal both the
size and kbuf->next. The kbuffer_refresh() is to update the kbuf if more
data was added to the buffer. But if curr is at the end, the next pointer
was not updated, which is incorrect. The next pointer needs to be moved to
the end of the newly written event.

Update the pointers in kbuffer_refresh() just as if it was loaded new (but
still keeping curr at the correct location).

Link: https://lore.kernel.org/linux-trace-devel/ZZfJQTOyl0dHiTU-@google.com/

Reported-by: Vincent Donnefort <vdonnefort@google.com>
Fixes: 7a4d5b24 ("kbuffer: Add kbuffer_refresh() API")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 src/kbuffer-parse.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/kbuffer-parse.c b/src/kbuffer-parse.c
index 4801d432c58c..1e1d168b534c 100644
--- a/src/kbuffer-parse.c
+++ b/src/kbuffer-parse.c
@@ -299,6 +299,9 @@ void kbuffer_free(struct kbuffer *kbuf)
 	free(kbuf);
 }
 
+static unsigned int old_update_pointers(struct kbuffer *kbuf);
+static unsigned int update_pointers(struct kbuffer *kbuf);
+
 /**
  * kbuffer_refresh - update the meta data from the subbuffer
  * @kbuf; The kbuffer to update
@@ -309,13 +312,24 @@ void kbuffer_free(struct kbuffer *kbuf)
 int kbuffer_refresh(struct kbuffer *kbuf)
 {
 	unsigned long long flags;
+	unsigned int old_size;
 
 	if (!kbuf || !kbuf->subbuffer)
 		return -1;
 
+	old_size = kbuf->size;
+
 	flags = read_long(kbuf, kbuf->subbuffer + 8);
 	kbuf->size = (unsigned int)flags & COMMIT_MASK;
 
+	/* Update next to be the next element */
+	if (kbuf->size != old_size && kbuf->curr == old_size) {
+		if (kbuf->flags & KBUFFER_FL_OLD_FORMAT)
+			old_update_pointers(kbuf);
+		else
+			update_pointers(kbuf);
+	}
+
 	return 0;
 }
 
-- 
2.42.0

Re: [PATCH 3/3] kbuffer: Update kbuf->next in kbuffer_refresh()

[Vincent Donnefort]

On Fri, Jan 05, 2024 at 02:37:44PM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
> 
> If the kbuffer was read to completion, the kbuf->curr would equal both the
> size and kbuf->next. The kbuffer_refresh() is to update the kbuf if more
> data was added to the buffer. But if curr is at the end, the next pointer
> was not updated, which is incorrect. The next pointer needs to be moved to
> the end of the newly written event.
> 
> Update the pointers in kbuffer_refresh() just as if it was loaded new (but
> still keeping curr at the correct location).
> 
> Link: https://lore.kernel.org/linux-trace-devel/ZZfJQTOyl0dHiTU-@google.com/
> 
> Reported-by: Vincent Donnefort <vdonnefort@google.com>
> Fixes: 7a4d5b24 ("kbuffer: Add kbuffer_refresh() API")
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>  src/kbuffer-parse.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/src/kbuffer-parse.c b/src/kbuffer-parse.c
> index 4801d432c58c..1e1d168b534c 100644
> --- a/src/kbuffer-parse.c
> +++ b/src/kbuffer-parse.c
> @@ -299,6 +299,9 @@ void kbuffer_free(struct kbuffer *kbuf)
>  	free(kbuf);
>  }
>  
> +static unsigned int old_update_pointers(struct kbuffer *kbuf);
> +static unsigned int update_pointers(struct kbuffer *kbuf);
> +
>  /**
>   * kbuffer_refresh - update the meta data from the subbuffer
>   * @kbuf; The kbuffer to update
> @@ -309,13 +312,24 @@ void kbuffer_free(struct kbuffer *kbuf)
>  int kbuffer_refresh(struct kbuffer *kbuf)
>  {
>  	unsigned long long flags;
> +	unsigned int old_size;
>  
>  	if (!kbuf || !kbuf->subbuffer)
>  		return -1;
>  
> +	old_size = kbuf->size;
> +
>  	flags = read_long(kbuf, kbuf->subbuffer + 8);
>  	kbuf->size = (unsigned int)flags & COMMIT_MASK;
>  
> +	/* Update next to be the next element */
> +	if (kbuf->size != old_size && kbuf->curr == old_size) {
> +		if (kbuf->flags & KBUFFER_FL_OLD_FORMAT)
> +			old_update_pointers(kbuf);
> +		else
> +			update_pointers(kbuf);
> +	}
> +
>  	return 0;
>  }

I've been trying the new stack but I see some weird unexpected events:

$ echo 3 > /sys/kernel/debug/tracing/trace_marker

<...>-5 44401.178473328 mmiotrace_rw: 0 0 0 0 0 0     // I clearly didn't enable this event
<...>-208 44401.178473328       print: tracing_mark_write: 2


Looking closer at the kbuf I see before the kbuffer_refresh()

  index = 244, curr = 272, next = 272, size = 272, start = 16

And after

  index = 280, curr = 272, next = 280, size = 312, start = 16

Could this index be the problem as this is used in kbuffer_read_event()?

>  
> -- 
> 2.42.0
> 

Re: [PATCH 3/3] kbuffer: Update kbuf->next in kbuffer_refresh()

[Vincent Donnefort]

On Fri, Jan 05, 2024 at 09:01:28PM +0000, Vincent Donnefort wrote:
> On Fri, Jan 05, 2024 at 02:37:44PM -0500, Steven Rostedt wrote:
> > From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
> > 
> > If the kbuffer was read to completion, the kbuf->curr would equal both the
> > size and kbuf->next. The kbuffer_refresh() is to update the kbuf if more
> > data was added to the buffer. But if curr is at the end, the next pointer
> > was not updated, which is incorrect. The next pointer needs to be moved to
> > the end of the newly written event.
> > 
> > Update the pointers in kbuffer_refresh() just as if it was loaded new (but
> > still keeping curr at the correct location).
> > 
> > Link: https://lore.kernel.org/linux-trace-devel/ZZfJQTOyl0dHiTU-@google.com/
> > 
> > Reported-by: Vincent Donnefort <vdonnefort@google.com>
> > Fixes: 7a4d5b24 ("kbuffer: Add kbuffer_refresh() API")
> > Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> > ---
> >  src/kbuffer-parse.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> > 
> > diff --git a/src/kbuffer-parse.c b/src/kbuffer-parse.c
> > index 4801d432c58c..1e1d168b534c 100644
> > --- a/src/kbuffer-parse.c
> > +++ b/src/kbuffer-parse.c
> > @@ -299,6 +299,9 @@ void kbuffer_free(struct kbuffer *kbuf)
> >  	free(kbuf);
> >  }
> >  
> > +static unsigned int old_update_pointers(struct kbuffer *kbuf);
> > +static unsigned int update_pointers(struct kbuffer *kbuf);
> > +
> >  /**
> >   * kbuffer_refresh - update the meta data from the subbuffer
> >   * @kbuf; The kbuffer to update
> > @@ -309,13 +312,24 @@ void kbuffer_free(struct kbuffer *kbuf)
> >  int kbuffer_refresh(struct kbuffer *kbuf)
> >  {
> >  	unsigned long long flags;
> > +	unsigned int old_size;
> >  
> >  	if (!kbuf || !kbuf->subbuffer)
> >  		return -1;
> >  
> > +	old_size = kbuf->size;
> > +
> >  	flags = read_long(kbuf, kbuf->subbuffer + 8);
> >  	kbuf->size = (unsigned int)flags & COMMIT_MASK;
> >  
> > +	/* Update next to be the next element */
> > +	if (kbuf->size != old_size && kbuf->curr == old_size) {
> > +		if (kbuf->flags & KBUFFER_FL_OLD_FORMAT)
> > +			old_update_pointers(kbuf);
> > +		else
> > +			update_pointers(kbuf);
> > +	}
> > +
> >  	return 0;
> >  }
> 
> I've been trying the new stack but I see some weird unexpected events:
> 
> $ echo 3 > /sys/kernel/debug/tracing/trace_marker
> 
> <...>-5 44401.178473328 mmiotrace_rw: 0 0 0 0 0 0     // I clearly didn't enable this event
> <...>-208 44401.178473328       print: tracing_mark_write: 2
> 
> 
> Looking closer at the kbuf I see before the kbuffer_refresh()
> 
>   index = 244, curr = 272, next = 272, size = 272, start = 16
> 
> And after
> 
>   index = 280, curr = 272, next = 280, size = 312, start = 16
> 
> Could this index be the problem as this is used in kbuffer_read_event()?

Yeah it seems that the update_pointers() is not enough. 

kbuffer_next_event(kbuf, NULL) will make sure curr is also up to date and will
do the update until an event type we can read. With that change I don't see any
spurious "mmiotrace_rw" on the output.

> 
> >  
> > -- 
> > 2.42.0
> > 

Re: [PATCH 3/3] kbuffer: Update kbuf->next in kbuffer_refresh()

[Steven Rostedt]

On Mon, 8 Jan 2024 11:11:29 +0000
Vincent Donnefort <vdonnefort@google.com> wrote:

> Yeah it seems that the update_pointers() is not enough. 
> 
> kbuffer_next_event(kbuf, NULL) will make sure curr is also up to date and will
> do the update until an event type we can read. With that change I don't see any
> spurious "mmiotrace_rw" on the output.


Ah you're right. Try this.

-- Steve

diff --git a/src/kbuffer-parse.c b/src/kbuffer-parse.c
index 1e1d168..5651797 100644
--- a/src/kbuffer-parse.c
+++ b/src/kbuffer-parse.c
@@ -180,6 +180,7 @@ static int calc_index(struct kbuffer *kbuf, void *ptr)
 	return (unsigned long)ptr - (unsigned long)kbuf->data;
 }
 
+static int next_event(struct kbuffer *kbuf);
 static int __next_event(struct kbuffer *kbuf);
 
 /*
@@ -323,12 +324,8 @@ int kbuffer_refresh(struct kbuffer *kbuf)
 	kbuf->size = (unsigned int)flags & COMMIT_MASK;
 
 	/* Update next to be the next element */
-	if (kbuf->size != old_size && kbuf->curr == old_size) {
-		if (kbuf->flags & KBUFFER_FL_OLD_FORMAT)
-			old_update_pointers(kbuf);
-		else
-			update_pointers(kbuf);
-	}
+	if (kbuf->size != old_size && kbuf->curr == kbuf->next)
+		next_event(kbuf);
 
 	return 0;
 }

Re: [PATCH 3/3] kbuffer: Update kbuf->next in kbuffer_refresh()

[Vincent Donnefort]

On Mon, Jan 08, 2024 at 11:28:53AM -0500, Steven Rostedt wrote:
> On Mon, 8 Jan 2024 11:11:29 +0000
> Vincent Donnefort <vdonnefort@google.com> wrote:
> 
> > Yeah it seems that the update_pointers() is not enough. 
> > 
> > kbuffer_next_event(kbuf, NULL) will make sure curr is also up to date and will
> > do the update until an event type we can read. With that change I don't see any
> > spurious "mmiotrace_rw" on the output.
> 
> 
> Ah you're right. Try this.
> 
> -- Steve
> 
> diff --git a/src/kbuffer-parse.c b/src/kbuffer-parse.c
> index 1e1d168..5651797 100644
> --- a/src/kbuffer-parse.c
> +++ b/src/kbuffer-parse.c
> @@ -180,6 +180,7 @@ static int calc_index(struct kbuffer *kbuf, void *ptr)
>  	return (unsigned long)ptr - (unsigned long)kbuf->data;
>  }
>  
> +static int next_event(struct kbuffer *kbuf);
>  static int __next_event(struct kbuffer *kbuf);
>  
>  /*
> @@ -323,12 +324,8 @@ int kbuffer_refresh(struct kbuffer *kbuf)
>  	kbuf->size = (unsigned int)flags & COMMIT_MASK;
>  
>  	/* Update next to be the next element */
> -	if (kbuf->size != old_size && kbuf->curr == old_size) {
> -		if (kbuf->flags & KBUFFER_FL_OLD_FORMAT)
> -			old_update_pointers(kbuf);
> -		else
> -			update_pointers(kbuf);
> -	}
> +	if (kbuf->size != old_size && kbuf->curr == kbuf->next)
> +		next_event(kbuf);
>  
>  	return 0;
>  }

That worked!