[PATCH 0/3] tracing/probes: Fix bugs in process_fetch_insn

[PATCH 0/3] tracing/probes: Fix bugs in process_fetch_insn

[Masami Hiramatsu (Google)]

Hi,

Here are some patches to fix bugs in process_fetch_insn_*(). 
First 2 fixes are already reviewed and updated the description.
I added 1 new patch which I found while fixing previous one.

Thank you,

---

Masami Hiramatsu (Google) (3):
      tracing/probes: Fix to avoid double count of the string length on the array
      tracing/probes: Fix to exit fetching if an error is detected
      tracing/probes: Fix return value when "(fault)" is injected


 kernel/trace/trace_probe_kernel.h                  |   17 +++++++----------
 kernel/trace/trace_probe_tmpl.h                    |    6 ++++--
 .../ftrace/test.d/kprobe/kprobe_args_user.tc       |    2 +-
 3 files changed, 12 insertions(+), 13 deletions(-)

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>

[PATCH 1/3] tracing/probes: Fix to avoid double count of the string length on the array

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

If an array is specified with the ustring or symstr, the length of the
strings are accumlated on both of 'ret' and 'total', which means the
length is double counted.
Just set the length to the 'ret' value to aviod double count.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/all/8819b154-2ba1-43c3-98a2-cbde20892023@moroto.mountain/
Fixes: 88903c464321 ("tracing/probe: Add ustring type for user-space string")
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace_probe_tmpl.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_probe_tmpl.h b/kernel/trace/trace_probe_tmpl.h
index 00707630788d..4735c5cb76fa 100644
--- a/kernel/trace/trace_probe_tmpl.h
+++ b/kernel/trace/trace_probe_tmpl.h
@@ -156,11 +156,11 @@ process_fetch_insn_bottom(struct fetch_insn *code, unsigned long val,
 			code++;
 			goto array;
 		case FETCH_OP_ST_USTRING:
-			ret += fetch_store_strlen_user(val + code->offset);
+			ret = fetch_store_strlen_user(val + code->offset);
 			code++;
 			goto array;
 		case FETCH_OP_ST_SYMSTR:
-			ret += fetch_store_symstrlen(val + code->offset);
+			ret = fetch_store_symstrlen(val + code->offset);
 			code++;
 			goto array;
 		default:

Re: [PATCH 1/3] tracing/probes: Fix to avoid double count of the string length on the array

[Masami Hiramatsu]

On Sun, 2 Jul 2023 17:44:38 +0200
Markus Elfring <Markus.Elfring@web.de> wrote:

> …
> > Just set the length to the 'ret' value to aviod double count.
> 
> Would the wording “… avoid double counting” be more appropriate
> for a subsequent change description?

Yeah, thanks!

> 
> Regards,
> Markus


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

[PATCH 2/3] tracing/probes: Fix to exit fetching if an error is detected

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Fix to exit fetching arguments if an error is detected when storing
strings. Without this fix, if an array is specified with string types
it may store the data at the wrong address.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/all/8819b154-2ba1-43c3-98a2-cbde20892023@moroto.mountain/
Fixes: 9b960a38835f ("tracing: probeevent: Unify fetch_insn processing common part")
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace_probe_tmpl.h |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/trace/trace_probe_tmpl.h b/kernel/trace/trace_probe_tmpl.h
index 4735c5cb76fa..d6f2bf69f9bc 100644
--- a/kernel/trace/trace_probe_tmpl.h
+++ b/kernel/trace/trace_probe_tmpl.h
@@ -193,6 +193,8 @@ process_fetch_insn_bottom(struct fetch_insn *code, unsigned long val,
 	default:
 		return -EILSEQ;
 	}
+	if (ret < 0)
+		return ret;
 	code++;
 
 	/* 4th stage: modify stored value if needed */

Re: [PATCH 2/3] tracing/probes: Fix to exit fetching if an error is detected

[Masami Hiramatsu]

On Sun,  2 Jul 2023 23:47:26 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> Fix to exit fetching arguments if an error is detected when storing
> strings. Without this fix, if an array is specified with string types
> it may store the data at the wrong address.
> 
> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> Closes: https://lore.kernel.org/all/8819b154-2ba1-43c3-98a2-cbde20892023@moroto.mountain/
> Fixes: 9b960a38835f ("tracing: probeevent: Unify fetch_insn processing common part")
> Cc: stable@vger.kernel.org
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>  kernel/trace/trace_probe_tmpl.h |    2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/trace/trace_probe_tmpl.h b/kernel/trace/trace_probe_tmpl.h
> index 4735c5cb76fa..d6f2bf69f9bc 100644
> --- a/kernel/trace/trace_probe_tmpl.h
> +++ b/kernel/trace/trace_probe_tmpl.h
> @@ -193,6 +193,8 @@ process_fetch_insn_bottom(struct fetch_insn *code, unsigned long val,
>  	default:
>  		return -EILSEQ;
>  	}
> +	if (ret < 0)
> +		return ret;

I found this will leave a garbage data on the trace data if we are in the array.
Let me fix this issue.
(-EILSEQ case has another issue. I think it should not be recorded)

Thank you,

>  	code++;
>  
>  	/* 4th stage: modify stored value if needed */
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

[PATCH 3/3] tracing/probes: Fix return value when "(fault)" is injected

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

When the "(fault)" is injected, the return value of fetch_store_string*()
should be the length of the "(fault)", but an error code is returned.
Fix it to return the correct length and update the data_loc according the
updated length.
This needs to update a ftracetest test case, which expects trace output
to appear as '(fault)' instead of '"(fault)"'.

Fixes: 2e9906f84fc7 ("tracing: Add "(fault)" name injection to kernel probes")
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 kernel/trace/trace_probe_kernel.h                  |   17 +++++++----------
 .../ftrace/test.d/kprobe/kprobe_args_user.tc       |    2 +-
 2 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/kernel/trace/trace_probe_kernel.h b/kernel/trace/trace_probe_kernel.h
index c4e1d4c03a85..63d90fe4eb87 100644
--- a/kernel/trace/trace_probe_kernel.h
+++ b/kernel/trace/trace_probe_kernel.h
@@ -48,14 +48,15 @@ fetch_store_strlen(unsigned long addr)
 	return (ret < 0) ? strlen(FAULT_STRING) + 1 : len;
 }
 
-static nokprobe_inline void set_data_loc(int ret, void *dest, void *__dest, void *base, int len)
+static nokprobe_inline int set_data_loc(int ret, void *dest, void *__dest, void *base, int len)
 {
-	if (ret >= 0) {
-		*(u32 *)dest = make_data_loc(ret, __dest - base);
-	} else {
+	if (ret < 0) {
 		strscpy(__dest, FAULT_STRING, len);
 		ret = strlen(__dest) + 1;
 	}
+
+	*(u32 *)dest = make_data_loc(ret, __dest - base);
+	return ret;
 }
 
 /*
@@ -76,9 +77,7 @@ fetch_store_string_user(unsigned long addr, void *dest, void *base)
 	__dest = get_loc_data(dest, base);
 
 	ret = strncpy_from_user_nofault(__dest, uaddr, maxlen);
-	set_data_loc(ret, dest, __dest, base, maxlen);
-
-	return ret;
+	return set_data_loc(ret, dest, __dest, base, maxlen);
 }
 
 /*
@@ -107,9 +106,7 @@ fetch_store_string(unsigned long addr, void *dest, void *base)
 	 * probing.
 	 */
 	ret = strncpy_from_kernel_nofault(__dest, (void *)addr, maxlen);
-	set_data_loc(ret, dest, __dest, base, maxlen);
-
-	return ret;
+	return set_data_loc(ret, dest, __dest, base, maxlen);
 }
 
 static nokprobe_inline int
diff --git a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_user.tc b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_user.tc
index d25d01a19778..8dcc0b29bd36 100644
--- a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_user.tc
+++ b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_user.tc
@@ -29,6 +29,6 @@ echo 1 > events/kprobes/myevent/enable
 ln -s foo $TMPDIR/bar
 echo 0 > events/kprobes/myevent/enable
 
-grep myevent trace | grep -q 'path=(fault) path2=(fault)'
+grep myevent trace | grep -q 'path="*(fault)"* path2="*(fault)"*'
 
 exit 0

Re: [PATCH 3/3] tracing/probes: Fix return value when "(fault)" is injected

[Steven Rostedt]

On Sun,  2 Jul 2023 23:47:35 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> When the "(fault)" is injected, the return value of fetch_store_string*()
> should be the length of the "(fault)", but an error code is returned.
> Fix it to return the correct length and update the data_loc according the
> updated length.
> This needs to update a ftracetest test case, which expects trace output
> to appear as '(fault)' instead of '"(fault)"'.
> 

Ah, because of patch 2, the ret < 0 makes it return without printing the
"fault"?

Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve


> Fixes: 2e9906f84fc7 ("tracing: Add "(fault)" name injection to kernel probes")
> Cc: stable@vger.kernel.org
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> ---

Re: [PATCH 3/3] tracing/probes: Fix return value when "(fault)" is injected

[Masami Hiramatsu]

On Wed, 5 Jul 2023 22:49:56 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Sun,  2 Jul 2023 23:47:35 +0900
> "Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:
> 
> > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > 
> > When the "(fault)" is injected, the return value of fetch_store_string*()
> > should be the length of the "(fault)", but an error code is returned.
> > Fix it to return the correct length and update the data_loc according the
> > updated length.
> > This needs to update a ftracetest test case, which expects trace output
> > to appear as '(fault)' instead of '"(fault)"'.
> > 
> 
> Ah, because of patch 2, the ret < 0 makes it return without printing the
> "fault"?

No, actually set_data_loc() updates the 'ret' argument, but it is just
disposed... (not returned to the caller)

-static nokprobe_inline void set_data_loc(int ret, void *dest, void *__dest, void *base, int len)
+static nokprobe_inline int set_data_loc(int ret, void *dest, void *__dest, void *base, int len)
 {
-	if (ret >= 0) {
-		*(u32 *)dest = make_data_loc(ret, __dest - base);
-	} else {
+	if (ret < 0) {
 		strscpy(__dest, FAULT_STRING, len);
 		ret = strlen(__dest) + 1;
 	}
+
+	*(u32 *)dest = make_data_loc(ret, __dest - base);
+	return ret;
 }

So this returns updated 'ret', and also update data_loc to use the
updated 'ret' value (which is the length of the stored data).

> 
> Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Thank you!

> 
> -- Steve
> 
> 
> > Fixes: 2e9906f84fc7 ("tracing: Add "(fault)" name injection to kernel probes")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > ---


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

Re: [PATCH 3/3] tracing/probes: Fix return value when "(fault)" is injected

[Steven Rostedt]

On Thu, 6 Jul 2023 13:40:36 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> On Wed, 5 Jul 2023 22:49:56 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> > On Sun,  2 Jul 2023 23:47:35 +0900
> > "Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:
> >   
> > > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > > 
> > > When the "(fault)" is injected, the return value of fetch_store_string*()
> > > should be the length of the "(fault)", but an error code is returned.
> > > Fix it to return the correct length and update the data_loc according the
> > > updated length.
> > > This needs to update a ftracetest test case, which expects trace output
> > > to appear as '(fault)' instead of '"(fault)"'.
> > >   
> > 
> > Ah, because of patch 2, the ret < 0 makes it return without printing the
> > "fault"?  
> 
> No, actually set_data_loc() updates the 'ret' argument, but it is just
> disposed... (not returned to the caller)

That's not what I was talking about.

We have:

process_fetch_insn_bottom() {
	[..]
	case FETCH_OP_ST_STRING:
		loc = *(u32 *)dest;
		ret = fetch_store_string(val + code->offset, dest, base);
		break;
	[..]

// And from patch 2 we have:

@@ -193,6 +193,8 @@ process_fetch_insn_bottom(struct fetch_insn *code, unsigned long val,
 	default:
 		return -EILSEQ;
 	}
+	if (ret < 0)
+		return ret;
 	code++;

And now that the return value of fetch_store_string() is being checked, and
if it returns negative, it ends the function before being processed
further. And if there's a fault, it happens to return negative!

This patch now changes fetch_store_string() and fetch_store_string_user()
to not return negative if there's a fault. As this patch has:

@@ -107,9 +106,7 @@ fetch_store_string(unsigned long addr, void *dest, void *base)
 	 * probing.
 	 */
 	ret = strncpy_from_kernel_nofault(__dest, (void *)addr, maxlen);
-	set_data_loc(ret, dest, __dest, base, maxlen);
-
-	return ret;
+	return set_data_loc(ret, dest, __dest, base, maxlen);
 }

But to do that, you needed to update set_data_loc() to return a value.

*that's* what I meant by 

'Ah, because of patch 2, the ret < 0 makes it return without printing the "fault"?'


-- Steve

> 
> -static nokprobe_inline void set_data_loc(int ret, void *dest, void *__dest, void *base, int len)
> +static nokprobe_inline int set_data_loc(int ret, void *dest, void *__dest, void *base, int len)
>  {
> -	if (ret >= 0) {
> -		*(u32 *)dest = make_data_loc(ret, __dest - base);
> -	} else {
> +	if (ret < 0) {
>  		strscpy(__dest, FAULT_STRING, len);
>  		ret = strlen(__dest) + 1;
>  	}
> +
> +	*(u32 *)dest = make_data_loc(ret, __dest - base);
> +	return ret;
>  }
> 
> So this returns updated 'ret', and also update data_loc to use the
> updated 'ret' value (which is the length of the stored data).
> 
> > 
> > Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>  
> 
> Thank you!
> 
> > 
> > -- Steve
> > 
> >   
> > > Fixes: 2e9906f84fc7 ("tracing: Add "(fault)" name injection to kernel probes")
> > > Cc: stable@vger.kernel.org
> > > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > > ---  
> 
> 

Re: [PATCH 3/3] tracing/probes: Fix return value when "(fault)" is injected

[Masami Hiramatsu]

On Thu, 6 Jul 2023 09:50:39 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Thu, 6 Jul 2023 13:40:36 +0900
> Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:
> 
> > On Wed, 5 Jul 2023 22:49:56 -0400
> > Steven Rostedt <rostedt@goodmis.org> wrote:
> > 
> > > On Sun,  2 Jul 2023 23:47:35 +0900
> > > "Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:
> > >   
> > > > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > > > 
> > > > When the "(fault)" is injected, the return value of fetch_store_string*()
> > > > should be the length of the "(fault)", but an error code is returned.
> > > > Fix it to return the correct length and update the data_loc according the
> > > > updated length.
> > > > This needs to update a ftracetest test case, which expects trace output
> > > > to appear as '(fault)' instead of '"(fault)"'.
> > > >   
> > > 
> > > Ah, because of patch 2, the ret < 0 makes it return without printing the
> > > "fault"?  
> > 
> > No, actually set_data_loc() updates the 'ret' argument, but it is just
> > disposed... (not returned to the caller)
> 
> That's not what I was talking about.
> 
> We have:
> 
> process_fetch_insn_bottom() {
> 	[..]
> 	case FETCH_OP_ST_STRING:
> 		loc = *(u32 *)dest;
> 		ret = fetch_store_string(val + code->offset, dest, base);
> 		break;
> 	[..]
> 
> // And from patch 2 we have:
> 
> @@ -193,6 +193,8 @@ process_fetch_insn_bottom(struct fetch_insn *code, unsigned long val,
>  	default:
>  		return -EILSEQ;
>  	}
> +	if (ret < 0)
> +		return ret;
>  	code++;
> 
> And now that the return value of fetch_store_string() is being checked, and
> if it returns negative, it ends the function before being processed
> further. And if there's a fault, it happens to return negative!
> 
> This patch now changes fetch_store_string() and fetch_store_string_user()
> to not return negative if there's a fault. As this patch has:
> 
> @@ -107,9 +106,7 @@ fetch_store_string(unsigned long addr, void *dest, void *base)
>  	 * probing.
>  	 */
>  	ret = strncpy_from_kernel_nofault(__dest, (void *)addr, maxlen);
> -	set_data_loc(ret, dest, __dest, base, maxlen);
> -
> -	return ret;
> +	return set_data_loc(ret, dest, __dest, base, maxlen);
>  }
> 
> But to do that, you needed to update set_data_loc() to return a value.
> 
> *that's* what I meant by 
> 
> 'Ah, because of patch 2, the ret < 0 makes it return without printing the "fault"?'

Yes, that's correct. Actually, the data ("(fault)") is stored, but ignored
because data_loc is not updated.

But wait, it seems that the print function shows (fault), so commit 2e9906f84fc7
("tracing: Add "(fault)" name injection to kernel probes") may not needed?

----
/* Print type function for string type */
int PRINT_TYPE_FUNC_NAME(string)(struct trace_seq *s, void *data, void *ent)
{
        int len = *(u32 *)data >> 16;

        if (!len)
                trace_seq_puts(s, "(fault)");
        else
----

In this case, what we need is to set data_loc length = 0 if ret < 0.

Do you really need to get '"(fault)"' (with double quotation) or
just '(fault)' (no double quotation) is OK?

Thank you,
> 
> 
> -- Steve
> 
> > 
> > -static nokprobe_inline void set_data_loc(int ret, void *dest, void *__dest, void *base, int len)
> > +static nokprobe_inline int set_data_loc(int ret, void *dest, void *__dest, void *base, int len)
> >  {
> > -	if (ret >= 0) {
> > -		*(u32 *)dest = make_data_loc(ret, __dest - base);
> > -	} else {
> > +	if (ret < 0) {
> >  		strscpy(__dest, FAULT_STRING, len);
> >  		ret = strlen(__dest) + 1;
> >  	}
> > +
> > +	*(u32 *)dest = make_data_loc(ret, __dest - base);
> > +	return ret;
> >  }
> > 
> > So this returns updated 'ret', and also update data_loc to use the
> > updated 'ret' value (which is the length of the stored data).
> > 
> > > 
> > > Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>  
> > 
> > Thank you!
> > 
> > > 
> > > -- Steve
> > > 
> > >   
> > > > Fixes: 2e9906f84fc7 ("tracing: Add "(fault)" name injection to kernel probes")
> > > > Cc: stable@vger.kernel.org
> > > > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > > > ---  
> > 
> > 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

Re: [PATCH 3/3] tracing/probes: Fix return value when "(fault)" is injected

[Steven Rostedt]

On Fri, 7 Jul 2023 11:02:10 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> /* Print type function for string type */
> int PRINT_TYPE_FUNC_NAME(string)(struct trace_seq *s, void *data, void *ent)
> {
>         int len = *(u32 *)data >> 16;
> 
>         if (!len)
>                 trace_seq_puts(s, "(fault)");
>         else
> ----
> 
> In this case, what we need is to set data_loc length = 0 if ret < 0.
> 
> Do you really need to get '"(fault)"' (with double quotation) or
> just '(fault)' (no double quotation) is OK?

 ># echo 'e:myopen syscalls/sys_enter_openat file=+0($filename):ustring' >> /sys/kernel/tracing/dynamic_events
 ># trace-cmd start -e myopen
 ># trace-cmd show
# tracer: nop
#
# entries-in-buffer/entries-written: 19/19   #P:4
#
#                                _-----=> irqs-off/BH-disabled
#                               / _----=> need-resched
#                              | / _---=> hardirq/softirq
#                              || / _--=> preempt-depth
#                              ||| / _-=> migrate-disable
#                              |||| /     delay
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |
       trace-cmd-4688    [000] ...1. 466968.015784: myopen: (syscalls.sys_enter_openat) file=(fault)
       trace-cmd-4688    [000] ...1. 466968.015816: myopen: (syscalls.sys_enter_openat) file=(fault)
       trace-cmd-4688    [000] ...1. 466968.015833: myopen: (syscalls.sys_enter_openat) file=(fault)
       trace-cmd-4688    [000] ...1. 466968.015849: myopen: (syscalls.sys_enter_openat) file=(fault)
       trace-cmd-4688    [000] ...1. 466968.015864: myopen: (syscalls.sys_enter_openat) file=(fault)
       trace-cmd-4688    [000] ...1. 466968.015879: myopen: (syscalls.sys_enter_openat) file=(fault)


Does that answer your question? ;-)

-- Steve

Re: [PATCH 3/3] tracing/probes: Fix return value when "(fault)" is injected

[Masami Hiramatsu]

On Thu, 6 Jul 2023 22:20:20 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Fri, 7 Jul 2023 11:02:10 +0900
> Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:
> 
> > /* Print type function for string type */
> > int PRINT_TYPE_FUNC_NAME(string)(struct trace_seq *s, void *data, void *ent)
> > {
> >         int len = *(u32 *)data >> 16;
> > 
> >         if (!len)
> >                 trace_seq_puts(s, "(fault)");
> >         else
> > ----
> > 
> > In this case, what we need is to set data_loc length = 0 if ret < 0.
> > 
> > Do you really need to get '"(fault)"' (with double quotation) or
> > just '(fault)' (no double quotation) is OK?
> 
>  ># echo 'e:myopen syscalls/sys_enter_openat file=+0($filename):ustring' >> /sys/kernel/tracing/dynamic_events
>  ># trace-cmd start -e myopen
>  ># trace-cmd show
> # tracer: nop
> #
> # entries-in-buffer/entries-written: 19/19   #P:4
> #
> #                                _-----=> irqs-off/BH-disabled
> #                               / _----=> need-resched
> #                              | / _---=> hardirq/softirq
> #                              || / _--=> preempt-depth
> #                              ||| / _-=> migrate-disable
> #                              |||| /     delay
> #           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
> #              | |         |   |||||     |         |
>        trace-cmd-4688    [000] ...1. 466968.015784: myopen: (syscalls.sys_enter_openat) file=(fault)
>        trace-cmd-4688    [000] ...1. 466968.015816: myopen: (syscalls.sys_enter_openat) file=(fault)
>        trace-cmd-4688    [000] ...1. 466968.015833: myopen: (syscalls.sys_enter_openat) file=(fault)
>        trace-cmd-4688    [000] ...1. 466968.015849: myopen: (syscalls.sys_enter_openat) file=(fault)
>        trace-cmd-4688    [000] ...1. 466968.015864: myopen: (syscalls.sys_enter_openat) file=(fault)
>        trace-cmd-4688    [000] ...1. 466968.015879: myopen: (syscalls.sys_enter_openat) file=(fault)
> 
> 
> Does that answer your question? ;-)

Ah, I meant that your commit 2e9906f84fc7 ("tracing: Add "(fault)" name injection
 to kernel probes") tries to make it '"(fault)"', So it makes 

       trace-cmd-4688    [000] ...1. 466968.015879: myopen: (syscalls.sys_enter_openat) file="(fault)"

Keeping it current '(fault)' makes easy to identify which one is failed to fetch,
but it may require user to parse both "some string" and (fault). I thought that
was the reason why you added that commit.

Thank you,

> 
> -- Steve


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

Re: [PATCH 3/3] tracing/probes: Fix return value when "(fault)" is injected

[Steven Rostedt]

On Fri, 7 Jul 2023 11:51:28 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> Ah, I meant that your commit 2e9906f84fc7 ("tracing: Add "(fault)" name injection
>  to kernel probes") tries to make it '"(fault)"', So it makes 
> 
>        trace-cmd-4688    [000] ...1. 466968.015879: myopen: (syscalls.sys_enter_openat) file="(fault)"
> 
> Keeping it current '(fault)' makes easy to identify which one is failed to fetch,
> but it may require user to parse both "some string" and (fault). I thought that
> was the reason why you added that commit.

Hmm, That commit didn't explicitly add the double quotes. That may just
have been a side effect of passing back the string?

But I agree, just (fault) instead of "(fault)" is more explicit that it
faulted.

-- Steve

Re: [PATCH 3/3] tracing/probes: Fix return value when "(fault)" is injected

[Masami Hiramatsu]

On Thu, 6 Jul 2023 23:06:42 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Fri, 7 Jul 2023 11:51:28 +0900
> Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:
> 
> > Ah, I meant that your commit 2e9906f84fc7 ("tracing: Add "(fault)" name injection
> >  to kernel probes") tries to make it '"(fault)"', So it makes 
> > 
> >        trace-cmd-4688    [000] ...1. 466968.015879: myopen: (syscalls.sys_enter_openat) file="(fault)"
> > 
> > Keeping it current '(fault)' makes easy to identify which one is failed to fetch,
> > but it may require user to parse both "some string" and (fault). I thought that
> > was the reason why you added that commit.
> 
> Hmm, That commit didn't explicitly add the double quotes. That may just
> have been a side effect of passing back the string?
> 
> But I agree, just (fault) instead of "(fault)" is more explicit that it
> faulted.

OK, let me revert that commit and clarify what the data_loc data should be
with fault case.

Thank you,

> 
> -- Steve


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>