linux-kernel - Re: [PATCH 1/2] drm/i915: Preallocate our mmu notifier workequeu to unbreak cpu hotplug deadlock

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Date:   Fri, 06 Oct 2017 10:23:46 +0100
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Daniel Vetter <daniel.vetter@...ll.ch>,
        "Intel Graphics Development" <intel-gfx@...ts.freedesktop.org>
Cc:     "LKML" <linux-kernel@...r.kernel.org>,
        "Daniel Vetter" <daniel.vetter@...ll.ch>,
        "Tvrtko Ursulin" <tvrtko.ursulin@...el.com>,
        "Joonas Lahtinen" <joonas.lahtinen@...ux.intel.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Sasha Levin" <alexander.levin@...izon.com>,
        "Marta Lofstedt" <marta.lofstedt@...el.com>,
        "Tejun Heo" <tj@...nel.org>,
        "Daniel Vetter" <daniel.vetter@...el.com>
Subject: Re: [PATCH 1/2] drm/i915: Preallocate our mmu notifier workequeu to unbreak
 cpu hotplug deadlock

Quoting Daniel Vetter (2017-10-06 10:06:36)
> 4.14-rc1 gained the fancy new cross-release support in lockdep, which
> seems to have uncovered a few more rules about what is allowed and
> isn't.
> 
> This one here seems to indicate that allocating a work-queue while
> holding mmap_sem is a no-go, so let's try to preallocate it.

But you haven't mentioned why we might want to preallocate to reduce the
mmap/mm_lock coverage anyway.
-Chris