linux-kernel - Re: "upping" a semaphore from interrupt context?

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Message-ID: <a781481a0706231002jf4467ebja6c28e3e242ceb76@mail.gmail.com>
Date:	Sat, 23 Jun 2007 22:32:55 +0530
From:	"Satyam Sharma" <satyam.sharma@...il.com>
To:	"Oliver Neukum" <oliver@...kum.org>
Cc:	"Arnd Bergmann" <arnd@...db.de>,
	"Robert P. J. Day" <rpjday@...dspring.com>,
	"Florin Iucha" <florin@...ha.net>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: "upping" a semaphore from interrupt context?

On 6/23/07, Oliver Neukum <oliver@...kum.org> wrote:
> Am Samstag, 23. Juni 2007 schrieb Satyam Sharma:
> > * 3. set up a timer and schedule another function to service the
> > * interrupt / do what needs to be done then, hopefully the mutex
> > * would be uncontended then => *gargh*
>
> You could use schedule_work(). However then why not use it always.
> This would make sense if what you want to do is outright trivial.

If you use schedule_work() to pass off work from interrupt context
to process context, then you wouldn't be calling down_trylock()
from interrupt context in the first place (which is what is being
discussed here). You would simply pass off the entire code that
uses the shared data (and wraps a *proper* down() or mutex_lock()
around it, not the _trylock() variant) to the workqueue.

Also, that is precisely my point too. What I'm saying is that it is
generally poor design to be wanting to use the _trylock() variant
of semaphore / mutex in interrupt context. Workqueues _are_ the
preferred mechanism to use for (most) such cases where you need
to do something that may require you to sleep.

Satyam
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