[PATCH 0/3] tracing/user_events: Fix incorrect return value for

[PATCH 0/3] tracing/user_events: Fix incorrect return value for

[sunliming]

Now the  writing operation return the count of writes whether events are
enabled or disabled. Fix this by just return -EFAULT when events are disabled.

sunliming (3):
  tracing/user_events: Fix incorrect return value for writing operation
    when events are disabled
  selftests/user_events: Enable the event before write_fault test in
    ftrace self-test
  selftests/user_events: Add test cases when event is disabled

 kernel/trace/trace_events_user.c                  | 3 ++-
 tools/testing/selftests/user_events/ftrace_test.c | 7 +++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

-- 
2.25.1

[PATCH 1/3] tracing/user_events: Fix incorrect return value for writing operation when events are disabled

[sunliming]

The writing operation return the count of writes whether events are
enabled or disabled. This is incorrect when events are disabled. Fix
this by just return -EFAULT when events are disabled.

Signed-off-by: sunliming <sunliming@kylinos.cn>
---
 kernel/trace/trace_events_user.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 1ac5ba5685ed..970bac0503fd 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -1957,7 +1957,8 @@ static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
 
 		if (unlikely(faulted))
 			return -EFAULT;
-	}
+	} else
+		return -EFAULT;
 
 	return ret;
 }
-- 
2.25.1

[PATCH 2/3] selftests/user_events: Enable the event before write_fault test in ftrace self-test

[sunliming]

The user_event has not be enabled in write_fault test in ftrace
self-test, Just enable it.

Signed-off-by: sunliming <sunliming@kylinos.cn>
---
 tools/testing/selftests/user_events/ftrace_test.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/testing/selftests/user_events/ftrace_test.c b/tools/testing/selftests/user_events/ftrace_test.c
index abfb49558a26..d33bd31425db 100644
--- a/tools/testing/selftests/user_events/ftrace_test.c
+++ b/tools/testing/selftests/user_events/ftrace_test.c
@@ -373,6 +373,10 @@ TEST_F(user, write_fault) {
 	ASSERT_EQ(0, ioctl(self->data_fd, DIAG_IOCSREG, &reg));
 	ASSERT_EQ(0, reg.write_index);
 
+	/* Enable event */
+	self->enable_fd = open(enable_file, O_RDWR);
+	ASSERT_NE(-1, write(self->enable_fd, "1", sizeof("1")))
+
 	/* Write should work normally */
 	ASSERT_NE(-1, writev(self->data_fd, (const struct iovec *)io, 2));
 
-- 
2.25.1

[PATCH 3/3] selftests/user_events: Add test cases when event is disabled

[sunliming]

When user_events are disabled, it's write operation should be fail. Add
this test cases.

Signed-off-by: sunliming <sunliming@kylinos.cn>
---
 tools/testing/selftests/user_events/ftrace_test.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/testing/selftests/user_events/ftrace_test.c b/tools/testing/selftests/user_events/ftrace_test.c
index d33bd31425db..d3240a97f23d 100644
--- a/tools/testing/selftests/user_events/ftrace_test.c
+++ b/tools/testing/selftests/user_events/ftrace_test.c
@@ -297,6 +297,9 @@ TEST_F(user, write_events) {
 	io[0].iov_base = &reg.write_index;
 	io[0].iov_len = sizeof(reg.write_index);
 
+	/* Write should fail when event is not enabled */
+	ASSERT_EQ(-1, writev(self->data_fd, (const struct iovec *)io, 3));
+
 	/* Enable event */
 	self->enable_fd = open(enable_file, O_RDWR);
 	ASSERT_NE(-1, write(self->enable_fd, "1", sizeof("1")))
-- 
2.25.1

Re: [PATCH 1/3] tracing/user_events: Fix incorrect return value for writing operation when events are disabled

[Beau Belgrave]

On Thu, Jun 08, 2023 at 09:15:52AM +0800, sunliming wrote:
> The writing operation return the count of writes whether events are
> enabled or disabled. This is incorrect when events are disabled. Fix
> this by just return -EFAULT when events are disabled.
> 
> Signed-off-by: sunliming <sunliming@kylinos.cn>
> ---
>  kernel/trace/trace_events_user.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> index 1ac5ba5685ed..970bac0503fd 100644
> --- a/kernel/trace/trace_events_user.c
> +++ b/kernel/trace/trace_events_user.c
> @@ -1957,7 +1957,8 @@ static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
>  
>  		if (unlikely(faulted))
>  			return -EFAULT;
> -	}
> +	} else
> +		return -EFAULT;
>  

I'm not sure this is a good idea. Imagine this scenario:
A user process writes out a user_event and it hits a fault that gets
returned as errno (EFAULT).

The user process is likely to either forget it and say, not worth
retrying, or it will retry (potentially in a loop).

If the process does retry and it's now disabled, it might try many
times.

I think that -ENOENT is a better error to use here. That way a user
process will know it got disabled mid-write vs a fault that might want
to be re-attempted.

Thanks,
-Beau

>  	return ret;
>  }
> -- 
> 2.25.1

Re: [PATCH 3/3] selftests/user_events: Add test cases when event is disabled

[Beau Belgrave]

On Thu, Jun 08, 2023 at 09:15:54AM +0800, sunliming wrote:
> When user_events are disabled, it's write operation should be fail. Add
> this test cases.
> 
> Signed-off-by: sunliming <sunliming@kylinos.cn>
> ---
>  tools/testing/selftests/user_events/ftrace_test.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/tools/testing/selftests/user_events/ftrace_test.c b/tools/testing/selftests/user_events/ftrace_test.c
> index d33bd31425db..d3240a97f23d 100644
> --- a/tools/testing/selftests/user_events/ftrace_test.c
> +++ b/tools/testing/selftests/user_events/ftrace_test.c
> @@ -297,6 +297,9 @@ TEST_F(user, write_events) {
>  	io[0].iov_base = &reg.write_index;
>  	io[0].iov_len = sizeof(reg.write_index);
>  
> +	/* Write should fail when event is not enabled */
> +	ASSERT_EQ(-1, writev(self->data_fd, (const struct iovec *)io, 3));
> +

We should also check errno value in this case. See my reply in the other
patch about -EFAULT vs -ENOENT in this case.

Thanks,
-Beau

>  	/* Enable event */
>  	self->enable_fd = open(enable_file, O_RDWR);
>  	ASSERT_NE(-1, write(self->enable_fd, "1", sizeof("1")))
> -- 
> 2.25.1

Re: [PATCH 1/3] tracing/user_events: Fix incorrect return value for writing operation when events are disabled

[sunliming]

Beau Belgrave <beaub@linux.microsoft.com> 于2023年6月9日周五 01:19写道：
>
> On Thu, Jun 08, 2023 at 09:15:52AM +0800, sunliming wrote:
> > The writing operation return the count of writes whether events are
> > enabled or disabled. This is incorrect when events are disabled. Fix
> > this by just return -EFAULT when events are disabled.
> >
> > Signed-off-by: sunliming <sunliming@kylinos.cn>
> > ---
> >  kernel/trace/trace_events_user.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> > index 1ac5ba5685ed..970bac0503fd 100644
> > --- a/kernel/trace/trace_events_user.c
> > +++ b/kernel/trace/trace_events_user.c
> > @@ -1957,7 +1957,8 @@ static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
> >
> >               if (unlikely(faulted))
> >                       return -EFAULT;
> > -     }
> > +     } else
> > +             return -EFAULT;
> >
>
> I'm not sure this is a good idea. Imagine this scenario:
> A user process writes out a user_event and it hits a fault that gets
> returned as errno (EFAULT).
>
> The user process is likely to either forget it and say, not worth
> retrying, or it will retry (potentially in a loop).
>
> If the process does retry and it's now disabled, it might try many
> times.
>
> I think that -ENOENT is a better error to use here. That way a user
> process will know it got disabled mid-write vs a fault that might want
> to be re-attempted.
>
> Thanks,
> -Beau
>
I think you are right. I have resend the V2 version of this series of
patches based on suggestions,
patches link :
https://lore.kernel.org/linux-trace-kernel/20230609030302.1278716-1-sunliming@kylinos.cn/T/#t
Thanks.
> >       return ret;
> >  }
> > --
> > 2.25.1