linux-kernel - Re: [RFC][PATCH] drm: kirin: Add a mutex to avoid fb initialization race

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Message-ID: <CALAqxLVsO7JP+j1wSy_mM_Rf5S7Hx4Dueco6LD4qcqdDMAjv2A@mail.gmail.com>
Date:   Fri, 24 Feb 2017 13:33:23 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     liuxinliang <z.liuxinliang@...ilicon.com>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Rongrong Zou <zourongrong@...il.com>,
        Xinwei Kong <kong.kongxinwei@...ilicon.com>,
        Chen Feng <puck.chen@...ilicon.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Sean Paul <seanpaul@...omium.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [RFC][PATCH] drm: kirin: Add a mutex to avoid fb initialization race

On Thu, Feb 23, 2017 at 5:55 PM, liuxinliang
<z.liuxinliang@...ilicon.com> wrote:
> Hi John,
>
> On 2017/2/23 8:56, John Stultz wrote:
>>
>> In some cases I've been seeing a race where two framebuffers
>> would be initialized, as kirin_fbdev_output_poll_changed()
>> might get called quickly in succession, resulting in the fb
>> initialization happening twice. This could cause the system
>
>
> I might understand this race. This because two places call
> drm_helper_hpd_irq_event might cause the race:
> One place is here
> static int kirin_drm_kms_init(struct drm_device *dev)
> {
> ...
>     /* force detection after connectors init */
>     (void)drm_helper_hpd_irq_event(dev);
> ...
> }
>
> another is the adv7533 interrupt thread handler
> static int adv7511_irq_process(struct adv7511 *adv7511, bool process_hpd)
> {
> ...
>     if (process_hpd && irq0 & ADV7511_INT0_HPD && adv7511->bridge.encoder)
>         drm_helper_hpd_irq_event(adv7511->connector.dev);
> ...
> }
>
> right?
>
> I don't get a better way to fix this yet , I like to put fb_lock into
> kirin_drm_private.

Ok. I've moved the mutex to the kirin_drm_private structure.

Anything else you'd like to see before I resend?

thanks
-john