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Date: Tue, 14 Mar 2017 13:41:03 +0000
From: Chris Wilson <chris@chris-wilson.co.uk>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        David Airlie <airlied@linux.ie>, intel-gfx@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org
Subject: Re: [Intel-gfx] [linux-mmotm] i915_gem_userptr_get_pages: possible
 circular locking dependency detected
Message-ID: <20170314134103.GI2118@nuc-i3427.alporthouse.com>
Mail-Followup-To: Chris Wilson <chris@chris-wilson.co.uk>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Daniel Vetter <daniel.vetter@intel.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        David Airlie <airlied@linux.ie>, intel-gfx@lists.freedesktop.org,
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On Tue, Mar 14, 2017 at 10:21:09PM +0900, Sergey Senozhatsky wrote:
> Hello,
> 
> [  530.698622] ======================================================
> [  530.698623] WARNING: possible circular locking dependency detected
> [  530.698626] 4.11.0-rc2-mm1-dbg-00167-gdb8a9941614c-dirty #222 Not tainted
> [  530.698627] ------------------------------------------------------
> [  530.698628] Xorg/343 is trying to acquire lock:
> [  530.698630]  (&mm->mmap_sem){++++++}, at: [<ffffffffa057e085>] i915_gem_userptr_get_pages+0x60/0x29c [i915]
> [  530.698702] 
>                but task is already holding lock:
> [  530.698703]  (&obj->mm.lock){+.+.+.}, at: [<ffffffffa0572d78>] __i915_gem_object_get_pages+0x21/0x62 [i915]
> [  530.698763] 
>                which lock already depends on the new lock.

Yup, just seen it myself. This particular cycle is a non-issue, but
there is another possiblity for a mmap_sem recursion in the ggtt fault
handler.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre