linux-kernel - Re: [PATCH AUTOSEL 4.19 11/29] binder: take read mode of mmap_sem in binder_alloc_free

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Message-ID: <20190830073019.GA16891@elm>
Date:   Fri, 30 Aug 2019 02:30:19 -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 4.19 11/29] binder: take read mode of mmap_sem in
 binder_alloc_free_page()

On 2019-08-30 08:29:10, Greg Kroah-Hartman wrote:
> On Thu, Aug 29, 2019 at 10:13:20AM -0500, Tyler Hicks wrote:
> > Hello, Sasha!
> > 
> > On 2019-08-29 06:49:51, 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 4.19 since commit 3013bf62b67a
> > ("binder: reduce mmap_sem write-side lock") was never brought back to
> > 4.19.
> > 
> > Tyler
> > 
> > > 
> > > Fixes: 5cec2d2e5839 ("binder: fix race between munmap() and direct reclaim")
> 
> But this commit is in 4.19.49

That's correct but commit 3013bf62b67a isn't present in 4.19.y. See the
"Backporting note" above.

Tyler

> 
> thanks,
> 
> greg k-h