linux-kernel - Re: [HMM 12/15] mm/migrate: new memory migration helper for use with device memory v4

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Message-ID: <20170710234339.GA15226@redhat.com>
Date:   Mon, 10 Jul 2017 19:43:39 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     Evgeny Baskakov <ebaskakov@...dia.com>
Cc:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        John Hubbard <jhubbard@...dia.com>,
        David Nellans <dnellans@...dia.com>,
        Mark Hairgrove <mhairgrove@...dia.com>,
        Sherry Cheung <SCheung@...dia.com>,
        Subhash Gutti <sgutti@...dia.com>
Subject: Re: [HMM 12/15] mm/migrate: new memory migration helper for use with
 device memory v4

On Mon, Jul 10, 2017 at 03:59:37PM -0700, Evgeny Baskakov wrote:
> On 6/30/17 5:57 PM, Jerome Glisse wrote:
> ...
> 
> Hi Jerome,
> 
> I am seeing a strange crash in our code that uses the hmm_device_new()
> helper. After the driver is repeatedly loaded/unloaded, hmm_device_new()
> suddenly returns NULL.
> 
> I have reproduced this with the dummy driver from the hmm-next branch:
> 
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000208

Horrible stupid bug in the code, most likely from cut and paste. Attached
patch should fix it. I don't know how long it took for you to trigger it.

Jérôme

View attachment "0001-mm-hmm-fix-major-device-driver-exhaustion-dumb-cut-a.patch" of type "text/plain" (1202 bytes)