linux-kernel - Re: [PATCH] remoteproc: Don't bother checking the return value of debugfs

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Date:   Tue, 29 Mar 2022 21:05:22 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     bjorn.andersson@...aro.org, linux-remoteproc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] remoteproc: Don't bother checking the return value of
 debugfs_create*

On Tue, Mar 29, 2022 at 08:59:48AM -0600, Mathieu Poirier wrote:
> On Tue, 29 Mar 2022 at 08:31, Manivannan Sadhasivam
> <manivannan.sadhasivam@...aro.org> wrote:
> >
> > Hi Mathieu,
> >
> > On Mon, Mar 28, 2022 at 09:51:23AM -0600, Mathieu Poirier wrote:
> > > Hi Mani,
> > >
> > > On Thu, Mar 24, 2022 at 11:42:24PM +0530, Manivannan Sadhasivam wrote:
> > > > DebugFS APIs are designed to return only the error pointers and not NULL
> > > > in the case of failure. So these return pointers are safe to be passed on
> > > > to the successive debugfs_create* APIs.
> > > >
> > > > Therefore, let's just get rid of the checks.
> > > >
> > > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > > > ---
> > > >  drivers/remoteproc/remoteproc_debugfs.c | 17 ++---------------
> > > >  1 file changed, 2 insertions(+), 15 deletions(-)
> > > >
> > > > diff --git a/drivers/remoteproc/remoteproc_debugfs.c b/drivers/remoteproc/remoteproc_debugfs.c
> > > > index b5a1e3b697d9..2e2c4a31c154 100644
> > > > --- a/drivers/remoteproc/remoteproc_debugfs.c
> > > > +++ b/drivers/remoteproc/remoteproc_debugfs.c
> > > > @@ -386,16 +386,8 @@ void rproc_remove_trace_file(struct dentry *tfile)
> > > >  struct dentry *rproc_create_trace_file(const char *name, struct rproc *rproc,
> > > >                                    struct rproc_debug_trace *trace)
> > > >  {
> > > > -   struct dentry *tfile;
> > > > -
> > > > -   tfile = debugfs_create_file(name, 0400, rproc->dbg_dir, trace,
> > > > +   return debugfs_create_file(name, 0400, rproc->dbg_dir, trace,
> > > >                                 &trace_rproc_ops);
> > > > -   if (!tfile) {
> > > > -           dev_err(&rproc->dev, "failed to create debugfs trace entry\n");
> > > > -           return NULL;
> > > > -   }
> > > > -
> > > > -   return tfile;
> > >
> > > Please see this thread [1] for an earlier conversation on this topic.
> > >
> > > [1]. https://lore.kernel.org/lkml/20220105131022.25247-1-linmq006@gmail.com/T/
> > >
> >
> > Thanks for the pointer! I believe the conclusion was to return 0 here
> > and ignore the return from debugfs_create_file(). If that's the case, it looks
> > fine to me and I'll send a follow-up patch.
> 
> Correct.
> 
> >
> > > >  }
> > > >
> > > >  void rproc_delete_debug_dir(struct rproc *rproc)
> > > > @@ -411,8 +403,6 @@ void rproc_create_debug_dir(struct rproc *rproc)
> > > >             return;
> > > >
> > > >     rproc->dbg_dir = debugfs_create_dir(dev_name(dev), rproc_dbg);
> > > > -   if (!rproc->dbg_dir)
> > > > -           return;
> > > >
> > > >     debugfs_create_file("name", 0400, rproc->dbg_dir,
> > > >                         rproc, &rproc_name_ops);
> > > > @@ -430,11 +420,8 @@ void rproc_create_debug_dir(struct rproc *rproc)
> > > >
> > > >  void __init rproc_init_debugfs(void)
> > > >  {
> > > > -   if (debugfs_initialized()) {
> > > > +   if (debugfs_initialized())
> > > >             rproc_dbg = debugfs_create_dir(KBUILD_MODNAME, NULL);
> > > > -           if (!rproc_dbg)
> > > > -                   pr_err("can't create debugfs dir\n");
> > > > -   }
> > >
> > > The above two are fine since debugfs_create_file() and debugfs_create_dir() can
> > > deal with @parent being an error code.
> > >
> >
> > debugfs_create_* APIs would never return NULL, so these checks are wrong.
> > Moreover, Greg recommends not to check the return value for any of these
> > functions.
> >
> 
> When writing "the above two are fine", I meant that I am in agreement
> with your changes.  Reading my comment again I can see how it could be
> interpreted as "I don't think your changes are necessary", which isn't
> the case.
> 

Sorry for the misinterpretation. Will send v2.

Thanks,
Mani

> > I've found the mail thread where Greg explained the reasoning behind it:
> > https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1907800.html
> >
> 
> I'll bookmark this one as it is bound to come back again.
> 
> > Thanks,
> > Mani
> >
> > > Thanks,
> > > Mathieu
> > >
> > > >  }
> > > >
> > > >  void __exit rproc_exit_debugfs(void)
> > > > --
> > > > 2.25.1
> > > >