linux-kernel - Re: [PATCH 08/22] gpiolib: cdev: complete the irq/thread timestamp handshake

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Message-ID: <CAMpxmJVbiH9mh2c8aAS+GG9a76w9c0Nrrv-VDVhpo+wSyQ2NeQ@mail.gmail.com>
Date:   Wed, 24 Jun 2020 16:00:42 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Kent Gibson <warthog618@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH 08/22] gpiolib: cdev: complete the irq/thread timestamp handshake

wt., 23 cze 2020 o 06:02 Kent Gibson <warthog618@...il.com> napisał(a):
>
> Reset the timestamp field to 0 after using it in lineevent_irq_thread.
>
> The timestamp is set by lineevent_irq_handler and is tested by
> lineevent_irq_thread to determine if it is called from a nested theaded
> interrupt.
> lineevent_irq_thread is assuming that the nested, or otherwise, status
> of the IRQ is static, i.e. it is either always nested or never nested.
> This change removes that assumption, resetting the timestamp so it can
> be re-used to determine the nested state of subsequent interrupts.
>
> Signed-off-by: Kent Gibson <warthog618@...il.com>
>

This change makes sense to me but I'm having a hard time processing
the explanation. If we're requesting the interrupt and allocating the
lineevent state in the same function - how can we run into a situation
here the status of the irq would change like what you describe?

Bart