Re: [PATCH AUTOSEL 4.14 05/14] binder: take read mode of mmap_sem in binder_alloc_free_page()
From: Tyler Hicks
Date: Fri Aug 30 2019 - 03:34:09 EST
On 2019-08-30 08:23:49, Greg Kroah-Hartman wrote:
> On Thu, Aug 29, 2019 at 10:10:52AM -0500, Tyler Hicks wrote:
> > Hello, Sasha!
> > On 2019-08-29 06:50:34, Sasha Levin wrote:
> > > From: Tyler Hicks <tyhicks@xxxxxxxxxxxxx>
> > >
> > > [ Upstream commit 60d4885710836595192c42d3e04b27551d30ec91 ]
> > >
> > > Restore the behavior of locking mmap_sem for reading in
> > > binder_alloc_free_page(), as was first done in commit 3013bf62b67a
> > > ("binder: reduce mmap_sem write-side lock"). That change was
> > > inadvertently reverted by commit 5cec2d2e5839 ("binder: fix race between
> > > munmap() and direct reclaim").
> > >
> > > In addition, change the name of the label for the error path to
> > > accurately reflect that we're taking the lock for reading.
> > >
> > > Backporting note: This fix is only needed when *both* of the commits
> > > mentioned above are applied. That's an unlikely situation since they
> > > both landed during the development of v5.1 but only one of them is
> > > targeted for stable.
> > This patch isn't meant to be applied to 4.14 since commit 3013bf62b67a
> > ("binder: reduce mmap_sem write-side lock") was never brought back to
> > 4.14.
> But the patch says:
> Fixes: 5cec2d2e5839 ("binder: fix race between munmap() and direct reclaim")
> and that commit is in 4.14.124.
This patch fixes 5cec2d2e5839 but only when 3013bf62b67a is also
applied. If 3013bf62b67a isn't present, this patch shouldn't be
backported. 3013bf62b67a isn't in 4.14.y.
> greg k-h