lkml.org 
[lkml]   [2019]   [Feb]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] binder: reduce mmap_sem write-side lock
On Mon, Feb 18, 2019 at 09:32:08AM +0100, Greg KH wrote:
> 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@google.com>
> > Cc: Martijn Coenen <maco@android.com>
> > Cc: Arve Hjønnevåg <arve@android.com>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Signed-off-by: Minchan Kim <minchan@kernel.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?

It has been there for several years but no need to fix older kernels
because down_write of mmap_sem is technically not a bug to stop the
working of binder. Rather than, it's just abuse of the lock so
it's okay to fix only recent kernel.

Thanks.

\
 
 \ /
  Last update: 2019-02-18 11:48    [W:0.067 / U:0.156 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site