linux-kernel - Re: [PATCH] binder: Drop needless locking in binder

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Message-ID: <20170717125219.GA20205@kroah.com>
Date:   Mon, 17 Jul 2017 14:52:19 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Dmitry Safonov <dsafonov@...tuozzo.com>
Cc:     linux-kernel@...r.kernel.org, 0x7f454c46@...il.com,
        Al Viro <viro@...iv.linux.org.uk>,
        Arve Hjønnevåg <arve@...roid.com>,
        Riley Andrews <riandrews@...roid.com>,
        devel@...verdev.osuosl.org,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH] binder: Drop needless locking in binder_mmap()

On Mon, Jun 19, 2017 at 05:53:34PM +0300, Dmitry Safonov wrote:
> On 05/24/2017 05:51 PM, Dmitry Safonov wrote:
> > binder_mmap() protected proc->buffer from concurrent changes.
> > It was introduced with commit bd1eff9741af ("Staging: android: binder:
> > Fix crashes when sharing a binder file between processes").
> > 
> > The commit fixed such races alike:
> > 
> > task1
> > =====
> > fd = open("/dev/binder",..)
> > fork()
> > ---------------------------------------->task2
> >    |                                      =====
> > mmap(fd)				mmap(fd)
> > 
> > Afterwards the situation was changed with the commit a79f41ed9786
> > ("binder: don't allow mmap() by process other than proc->tsk").
> > That commit prohibited mmap'ing of fd, that was opened by some
> > other task.
> > That restriction has made locking in binder_mmap() unnecessary.
> > 
> > Cc: Al Viro <viro@...iv.linux.org.uk>
> > Cc: "Arve Hjønnevåg" <arve@...roid.com>
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Cc: Riley Andrews <riandrews@...roid.com>
> > Cc: devel@...verdev.osuosl.org
> > Cc: Android Kernel Team <kernel-team@...roid.com>
> > Signed-off-by: Dmitry Safonov <dsafonov@...tuozzo.com>
> > ---
> >   drivers/android/binder.c | 5 -----
> >   1 file changed, 5 deletions(-)
> 
> Ping?

The "break up the binder lock" patches should have now made this
obsolete, right?  If not, can you please rebase it on my
char-misc-testing tree and resend?

thanks,

greg k-h