linux-kernel - Re: [PATCH] binder: fix redefinition of seq

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Message-ID: <Ysg/h9rU1VZeVcZV@google.com>
Date:   Fri, 8 Jul 2022 14:30:31 +0000
From:   Carlos Llamas <cmllamas@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Christian Brauner <brauner@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        kernel-team@...roid.com, linux-kernel@...r.kernel.org,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] binder: fix redefinition of seq_file attributes

On Fri, Jul 08, 2022 at 08:00:50AM +0200, Greg Kroah-Hartman wrote:
> On Thu, Jul 07, 2022 at 09:21:52PM +0000, Carlos Llamas wrote:
> > On Mon, Jul 04, 2022 at 06:13:40PM +0200, Greg Kroah-Hartman wrote:
> > > On Fri, Jul 01, 2022 at 06:20:41PM +0000, Carlos Llamas wrote:
> > > > +	binder_for_each_debugfs_entry(db_entry) {
> > > > +		dentry = binderfs_create_file(binder_logs_root_dir,
> > > > +					      db_entry->name,
> > > > +					      db_entry->fops,
> > > > +					      db_entry->data);
> > > > +		if (IS_ERR(dentry)) {
> > > > +			ret = PTR_ERR(dentry);
> > > > +			goto out;
> > > > +		}
> > > 
> > > I know this is a copy of what is there already, but there is never a
> > > need to check the result of a debugfs_create_* call.  Just call it and
> > > move on, never "abort" based on the result of a debugfs call, that's not
> > > a good idea.
> > 
> > This is true, none of these debugfs files seem critical for mounting a
> > binderfs instance. I'm thinking init_binder_logs() should just return
> > void. I'm only a bit hesitant to completely ignore the return code as
> > users specifically ask for these files to be created via mount option
> > "stats". So probably a pr_warn is what is actually needed here.
> 
> That would just be too noisy, just let it go, no one cares :)

ok, convinced. I'll get rid of these checks.

> 
> > > So can you change this here, or want to send a follow-on patch that
> > > removes these checks?
> > 
> > Sure, I'll send a follow-on patch. I'm currently AFK so setting ETA for
> > next week until I can actually test this change.
> > 
> > > 
> > > >  	}
> > > >  
> > > >  	proc_log_dir = binderfs_create_dir(binder_logs_root_dir, "proc");
> > > 
> > > Also there's never a need to save a directory, you can always look it up
> > > when you want to remove it.
> > 
> > It seems this is a convenient way to share this path with binder which
> > otherwise doesn't know where binderfs was mounted. From having a quick
> > look it doesn't seem that we need to share all the details in struct
> > binderfs_info though. Maybe there is a better way to handle all this.
> 
> Why would you need to share this internally with anything, again, it can
> always be looked up if you need it.

I just looked into this and you are right. Binder can just take
sb->s_root and look up the entries as needed. This means we can also
unexport all the binderfs_info bits from the internal header. Great!

Thanks,
--
Carlos Llamas