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 <20230608011554.1181097-2-sunliming@kylinos.cn> <20230608171921.GA74@W11-BEAU-MD.localdomain>
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From:   sunliming <kelulanainsley@gmail.com>
Date:   Tue, 13 Jun 2023 13:52:29 +0800
Message-ID: <CAJncD7QWnPbbZTUVbKF2F6cZ-X96djvoo=6rHg5yVzF-S-cMTw@mail.gmail.com>
Subject: Re: [PATCH 1/3] tracing/user_events: Fix incorrect return value for
 writing operation when events are disabled
To:     Beau Belgrave <beaub@linux.microsoft.com>
Cc:     mhiramat@kernel.org, rostedt@goodmis.org, shuah@kernel.org,
        linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org
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Beau Belgrave <beaub@linux.microsoft.com> =E4=BA=8E2023=E5=B9=B46=E6=9C=889=
=E6=97=A5=E5=91=A8=E4=BA=94 01:19=E5=86=99=E9=81=93=EF=BC=9A
>
> 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_even=
ts_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-sunlimi=
ng@kylinos.cn/T/#t
Thanks.
> >       return ret;
> >  }
> > --
> > 2.25.1