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Message-ID: <CAMP5Xgegepv1nXKgj-mVDFWi-W0G0JBN0KdpHo4sKLv08HX6=A@mail.gmail.com> Date: Wed, 13 Sep 2017 17:08:47 -0700 From: Arve Hjønnevåg <arve@...roid.com> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Sherry Yang <sherryy@...roid.com>, LKML <linux-kernel@...r.kernel.org>, Todd Kjos <tkjos@...gle.com>, Martijn Coenen <maco@...gle.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Ingo Molnar <mingo@...nel.org>, Michal Hocko <mhocko@...e.com>, Vlastimil Babka <vbabka@...e.cz>, David Rientjes <rientjes@...gle.com>, Andrea Arcangeli <aarcange@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Andy Lutomirski <luto@...nel.org>, Oleg Nesterov <oleg@...hat.com>, Hoeun Ryu <hoeun.ryu@...il.com>, Christoph Lameter <cl@...ux.com>, Vegard Nossum <vegard.nossum@...cle.com>, Frederic Weisbecker <fweisbec@...il.com> Subject: Re: [PATCH] mm: Restore mmput_async On Wed, Sep 13, 2017 at 3:57 PM, Andrew Morton <akpm@...ux-foundation.org> wrote: > On Wed, 13 Sep 2017 18:44:11 -0400 Sherry Yang <sherryy@...roid.com> wrote: > >> On Wed, Sep 13, 2017 at 6:09 PM, Andrew Morton >> <akpm@...ux-foundation.org> wrote: >> > On Wed, 13 Sep 2017 17:59:27 -0400 Sherry Yang <sherryy@...roid.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
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