linux-kernel - Re: [PATCH] rtc: snvs: fix possible race condition

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Date:   Fri, 19 Jul 2019 19:04:21 +0000
From:   Trent Piepho <tpiepho@...inj.com>
To:     "linux-rtc@...r.kernel.org" <linux-rtc@...r.kernel.org>,
        "anson.huang@....com" <anson.huang@....com>,
        "a.zummo@...ertech.it" <a.zummo@...ertech.it>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "alexandre.belloni@...tlin.com" <alexandre.belloni@...tlin.com>,
        "aisheng.dong@....com" <aisheng.dong@....com>
CC:     "linux-imx@....com" <linux-imx@....com>
Subject: Re: [PATCH] rtc: snvs: fix possible race condition

On Fri, 2019-07-19 at 02:57 +0000, Anson Huang wrote:
> 
> > I do worry that handling the irq before the rtc device is registered could still
> > result in a crash.  From what I saw, the irq path in snvs only uses driver state
> > members that are fully initialized for the most part, and the allocated but
> > unregistered data->rtc is only used in one call to rtc_update_irq(), which
> > appears to be ok with this.
> > 
> > But it is not that hard to imagine that something could go into the rtc core
> > that assumes call like rtc_update_irq() are only made on registered devices.
> > 
> > If there was a way to do it, I think allocating the irq in a masked state and
> > then unmasking it as part of the final registration call to make the device go
> > live would be a safer and more general pattern.
> 
> It makes sense, I think we can just move the devm_request_irq() to after rtc_register_device(),
> It will make sure everything is ready before IRQ is enabled. Will send out a V2 patch. 

That will mean registering the rtc, then unregistering it if the irq
request fails.  More of a pain to write this failure path.

Alexandre, is it part of rtc core design that rtc_update_irq() might be
called on a rtc device that is properly allocated, but not registered
yet?