linux-kernel - Re: [PATCH AUTOSEL 4.14 05/14] binder: take read mode of mmap_sem in binder_alloc_free

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Date:   Fri, 30 Aug 2019 02:34:00 -0500
From:   Tyler Hicks <tyhicks@...onical.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Todd Kjos <tkjos@...roid.com>,
        devel@...verdev.osuosl.org
Subject: Re: [PATCH AUTOSEL 4.14 05/14] binder: take read mode of mmap_sem in
 binder_alloc_free_page()

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@...onical.com>
> > > 
> > > [ 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.

Tyler

> 
> thanks,
> 
> greg k-h