linux-kernel - Re: [PATCH 2/2] binderfs: remove separate device

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Date:   Thu, 31 Jan 2019 01:26:28 +0100
From:   Christian Brauner <christian@...uner.io>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     devel@...verdev.osuosl.org, tkjos@...roid.com,
        linux-kernel@...r.kernel.org, arve@...roid.com,
        joel@...lfernandes.org, maco@...roid.com, tkjos@...gle.com
Subject: Re: [PATCH 2/2] binderfs: remove separate device_initcall()

On Wed, Jan 30, 2019 at 10:17:39PM +0100, Greg KH wrote:
> On Wed, Jan 30, 2019 at 06:01:02PM +0100, Christian Brauner wrote:
> > On Wed, Jan 30, 2019 at 03:24:12PM +0100, Greg KH wrote:
> > > On Wed, Jan 23, 2019 at 12:41:16PM +0100, Christian Brauner wrote:
> > > > binderfs should not have a separate device_initcall(). When a kernel is
> > > > compiled with CONFIG_ANDROID_BINDERFS register the filesystem alongside
> > > > CONFIG_ANDROID_IPC. This use-case is especially sensible when users specify
> > > > CONFIG_ANDROID_IPC=y, CONFIG_ANDROID_BINDERFS=y and
> > > > ANDROID_BINDER_DEVICES="".
> > > > When CONFIG_ANDROID_BINDERFS=n then this always succeeds so there's no
> > > > regression potential for legacy workloads.
> > > > 
> > > > Signed-off-by: Christian Brauner <christian@...uner.io>
> > > > ---
> > > >  drivers/android/binder.c          | 4 ++++
> > > >  drivers/android/binder_internal.h | 9 +++++++++
> > > >  drivers/android/binderfs.c        | 4 +---
> > > >  3 files changed, 14 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> > > > index cdfc87629efb..751d76173f81 100644
> > > > --- a/drivers/android/binder.c
> > > > +++ b/drivers/android/binder.c
> > > > @@ -5915,6 +5915,10 @@ static int __init binder_init(void)
> > > >  			goto err_init_binder_device_failed;
> > > >  	}
> > > >  
> > > > +	ret = init_binderfs();
> > > > +	if (ret)
> > > > +		goto err_init_binder_device_failed;
> > > > +
> > > >  	return ret;
> > > >  
> > > >  err_init_binder_device_failed:
> > > > diff --git a/drivers/android/binder_internal.h b/drivers/android/binder_internal.h
> > > > index 7fb97f503ef2..045b3e42d98b 100644
> > > > --- a/drivers/android/binder_internal.h
> > > > +++ b/drivers/android/binder_internal.h
> > > > @@ -46,4 +46,13 @@ static inline bool is_binderfs_device(const struct inode *inode)
> > > >  }
> > > >  #endif
> > > >  
> > > > +#ifdef CONFIG_ANDROID_BINDERFS
> > > > +extern int __init init_binderfs(void);
> > > > +#else
> > > > +static inline int __init init_binderfs(void)
> > > > +{
> > > > +	return 0;
> > > > +}
> > > > +#endif
> > > > +
> > > >  #endif /* _LINUX_BINDER_INTERNAL_H */
> > > > diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
> > > > index 7a550104a722..e773f45d19d9 100644
> > > > --- a/drivers/android/binderfs.c
> > > > +++ b/drivers/android/binderfs.c
> > > > @@ -550,7 +550,7 @@ static struct file_system_type binder_fs_type = {
> > > >  	.fs_flags	= FS_USERNS_MOUNT,
> > > >  };
> > > >  
> > > > -static int __init init_binderfs(void)
> > > > +int __init init_binderfs(void)
> > > >  {
> > > >  	int ret;
> > > >  
> > > > @@ -568,5 +568,3 @@ static int __init init_binderfs(void)
> > > >  
> > > >  	return ret;
> > > >  }
> > > > -
> > > > -device_initcall(init_binderfs);
> > > 
> > > I get a build warning when applying this patch :(
> > 
> > Hm, I can't reproduce that build error with this patch applied to what
> > you currently have in char-misc-linus. :(
> > Any chance you can give me the config that produced this warning?
> > I tried with CONFIG_BINDERFS=y and CONFIG_BINDERFS=n.
> 
> $ make M=drivers/android
>   CC      drivers/android/binderfs.o
>   CC      drivers/android/binder.o
> drivers/android/binder.c: In function ‘binder_init’:
> drivers/android/binder.c:5933:2: warning: ‘device_names’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>   kfree(device_names);
>   ^~~~~~~~~~~~~~~~~~~
> 
> $ gcc --version
> gcc (GCC) 8.2.1 20181127
> 
> And gcc is right about this warning, that could happen with your change :(

Thanks for the pointer. New version sent out that fixes this issue! :)

Thanks!
Christian