Subject: Re: [PATCH] iwlwifi: remove input device and fix rfkill state
From: Zhu Yi <yi.zhu@intel.com>
To: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Ivo van Doorn <ivdoorn@gmail.com>,
	Adel Gadllah <adel.gadllah@gmail.com>,
	linux-wireless@vger.kernel.org, randy.dunlap@oracle.com,
	"John W. Linville" <linville@tuxdriver.com>, fcrespel@gmail.com
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Date: Thu, 03 Jul 2008 11:11:11 +0800
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On Wed, 2008-07-02 at 22:53 -0300, Henrique de Moraes Holschuh wrote:
> Hmm, it could cause deadlocks I think.  task context takes lock.
> interrupt context tries to run, needs lock, keeps spinning forever
> waiting for it, and if we are not SMP, task context never has a chance
> to release the lock, so we get a deadlock.  Is this correct?

Never heard of spin_lock_irqsave()?

> If it is, we better make the atomic path lock-free.  Argh.  This means
> rfkill->state (the only thing we care about in the atomic path) would
> have to become an atomic variable, and the code changed to cope with
> its value being "volatile", so that it can be used in a lockless
> fashion.

Yup, if protecting rfkill->state is the only intention, a spinlock is
too heavy. set|clear_bit is enough if organizing the state into bitmaps.
BTW, read/write 32-bits aligned on x86 is already atomic.

Thanks,
-yi