MIME-Version: 1.0
In-Reply-To: <20170913155754.b072c04bbabffab0471a1ee2@linux-foundation.org>
References: <20170908223934.67442-1-sherryy@android.com> <20170913215932.86846-1-sherryy@android.com>
 <20170913150904.90a37a966a04ea394a2c3d9b@linux-foundation.org>
 <CAOUJ4O+NpiwTNeALOoH19DoBwv-HG3HvetrhuXY9weLXuo3bkQ@mail.gmail.com> <20170913155754.b072c04bbabffab0471a1ee2@linux-foundation.org>
From: =?UTF-8?B?QXJ2ZSBIasO4bm5ldsOlZw==?= <arve@android.com>
Date: Wed, 13 Sep 2017 17:08:47 -0700
Message-ID: <CAMP5Xgegepv1nXKgj-mVDFWi-W0G0JBN0KdpHo4sKLv08HX6=A@mail.gmail.com>
Subject: Re: [PATCH] mm: Restore mmput_async
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Sherry Yang <sherryy@android.com>, LKML <linux-kernel@vger.kernel.org>,
        Todd Kjos <tkjos@google.com>, Martijn Coenen <maco@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ingo Molnar <mingo@kernel.org>, Michal Hocko <mhocko@suse.com>,
        Vlastimil Babka <vbabka@suse.cz>, David Rientjes <rientjes@google.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andy Lutomirski <luto@kernel.org>, Oleg Nesterov <oleg@redhat.com>,
        Hoeun Ryu <hoeun.ryu@gmail.com>, Christoph Lameter <cl@linux.com>,
        Vegard Nossum <vegard.nossum@oracle.com>,
        Frederic Weisbecker <fweisbec@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Content-Transfer-Encoding: 8bit
Content-Length: 1495
Lines: 37

On Wed, Sep 13, 2017 at 3:57 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Wed, 13 Sep 2017 18:44:11 -0400 Sherry Yang <sherryy@android.com> wrote:
>
>> On Wed, Sep 13, 2017 at 6:09 PM, Andrew Morton
>> <akpm@linux-foundation.org> wrote:
>> > On Wed, 13 Sep 2017 17:59:27 -0400 Sherry Yang <sherryy@android.com> wrote:
>> >
>> >> Restore asynchronous mmput, allowing mmput_async to be called
>> >> from an atomic context in Android binder shrinker callback.
>> >>
>> >> mmput_async was initially introduced in ec8d7c14e
>> >> ("mm, oom_reaper: do not mmput synchronously from the
>> >> oom reaper context"), and was removed in 212925802
>> >> ("mm: oom: let oom_reap_task and exit_mmap run concurrently")
>> >
>> > Presumably there's a patch somewhere which adds a call to mmput_async()
>> > into drivers/android/binder.c?  Where is that patch?
>>
>> The patch that uses mmput_async() is
>> https://lkml.org/lkml/2017/9/8/785. Gmail doesn't seem to respect
>> in-reply-to.
>
> (Top-posting repaired.  Please don't!)
>
> Is it necessary for binder_alloc_free_page() to take a ref on the mm?
> As long as alloc->tsk doesn't exit during binder_alloc_free_page()'s
> execution, that task's reference on the mm should be sufficient to keep
> the mm alive?
>

alloc->tsk can exit during binder_alloc_free_page. We don't hold a
reference to the task's mm struct while we don't actively use it, as
this would prevent the driver from getting closed when a process dies.

-- 
Arve Hjønnevåg