linux-kernel - Re: [PATCH 2/3] serial: stm32: fix threaded interrupt handling

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Date:   Fri, 16 Apr 2021 16:46:02 +0200
From:   Johan Hovold <johan@...nel.org>
To:     dillon min <dillon.minfei@...il.com>
Cc:     Alexandre TORGUE <alexandre.torgue@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Erwan Le Ray <erwan.leray@...s.st.com>,
        Gerald Baeza <gerald.baeza@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH 2/3] serial: stm32: fix threaded interrupt handling

On Fri, Apr 16, 2021 at 10:35:25PM +0800, dillon min wrote:
> Hi Johan
> 
> Thanks for share your patch.
> 
> Johan Hovold <johan@...nel.org>于2021年4月16日 周五22:11写道：
> 
> > When DMA is enabled the receive handler runs in a threaded handler, but
> > the primary handler up until very recently neither disabled interrupts
> > in the device or used IRQF_ONESHOT. This would lead to a deadlock if an
> > interrupt comes in while the threaded receive handler is running under
> > the port lock.
> >
> Greg told me there was a patch fixed this case. In case hard irq &
> threaded_fn both offered. The local_irq_save() will be executed before call
> driver’s threaded handler.
> 
> Post the original mail from Greg
> 
> Please see 81e2073c175b ("genirq: Disable interrupts for force threaded
> handlers") for when threaded irq handlers have irqs disabled, isn't that
> the case you are trying to "protect" from here?
> 
> Why is the "threaded" flag used at all?  The driver should not care.
> 
> Also see 9baedb7baeda ("serial: imx: drop workaround for forced irq
> threading") in linux-next for an example of how this was fixed up in a
> serial driver.

Neither of these commits are (directly) related to the problem this
patch addresses (they are about force-threaded handlers, this is about a
normal threaded handler which run with interrupts enabled).

Johan