linux-kernel - Re: LTTng "TIF_KERNEL

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Message-ID: <alpine.DEB.2.00.0904281251210.8066@gandalf.stny.rr.com>
Date:	Tue, 28 Apr 2009 12:52:30 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Ingo Molnar <mingo@...e.hu>, Li Zefan <lizf@...fujitsu.com>,
	linux-kernel@...r.kernel.org
Subject: Re: LTTng "TIF_KERNEL_TRACE"


On Tue, 28 Apr 2009, Frederic Weisbecker wrote:

> On Tue, Apr 28, 2009 at 12:38:25PM -0400, Mathieu Desnoyers wrote:
> > No, read-write lock is a "special case" where it does not deadlock if
> > you have an interrupt handler taking the read lock over another read
> > lock. It's just the write lock that _must absolutely_ disable
> > interrupts.
> 
> 
> Ah, you're right, I was thinking with spinlock rules in mind :)
> 

The only time you would want to do a read_lock_irqsave is if the 
write_lock is taken in irq context. But I do not know of any lock where 
that is the case.

-- Steve

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