linux-kernel - Re: [PATCH] binder: reduce mmap

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Message-ID: <20190218083208.GA20069@kroah.com>
Date:   Mon, 18 Feb 2019 09:32:08 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, Todd Kjos <tkjos@...gle.com>,
        Martijn Coenen <maco@...roid.com>,
        Arve Hjønnevåg <arve@...roid.com>
Subject: Re: [PATCH] binder: reduce mmap_sem write-side lock

On Mon, Feb 18, 2019 at 05:11:45PM +0900, Minchan Kim wrote:
> binder has used write-side mmap_sem semaphore to release memory
> mapped at address space of the process. However, right lock to
> release pages is down_read, not down_write because page table lock
> already protects the race for parallel freeing.
> 
> Please do not use mmap_sem write-side lock which is well known
> contented lock.
> 
> Cc: Todd Kjos <tkjos@...gle.com>
> Cc: Martijn Coenen <maco@...roid.com>
> Cc: Arve Hjønnevåg <arve@...roid.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
>  drivers/android/binder_alloc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Is this just needed for the recent binder changes that are in
linux-next, or for older kernels as well?

thanks,

greg k-h