Re: [PATCH] binder: reduce mmap_sem write-side lock

[Greg KH]

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@xxxxxxxxxx>
> Cc: Martijn Coenen <maco@xxxxxxxxxxx>
> Cc: Arve Hjønnevåg <arve@xxxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> ---
>  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