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

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Message-ID: <CAJncD7QWnPbbZTUVbKF2F6cZ-X96djvoo=6rHg5yVzF-S-cMTw@mail.gmail.com>
Date:   Tue, 13 Jun 2023 13:52:29 +0800
From:   sunliming <kelulanainsley@...il.com>
To:     Beau Belgrave <beaub@...ux.microsoft.com>
Cc:     mhiramat@...nel.org, rostedt@...dmis.org, shuah@...nel.org,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 1/3] tracing/user_events: Fix incorrect return value for
 writing operation when events are disabled

Beau Belgrave <beaub@...ux.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@...inos.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