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Subject: Re: in_atomic() & spin_lock / spin_unlock in different functions
From: Robert Love <rml@tech9.net>
To: Pavel Machek <pavel@ucw.cz>
Cc: kernel list <linux-kernel@vger.kernel.org>
In-Reply-To: <20021013203838.A122@elf.ucw.cz>
References: <20021013203838.A122@elf.ucw.cz>
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Date: 13 Oct 2002 15:40:09 -0400
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On Sun, 2002-10-13 at 14:38, Pavel Machek wrote:

> I'm doing spin_lock_irqsave() then in another function
> spin_unlock_irqrestore. Is that okay? If no, can it cause "scheduling
> in atomic"?

It is not OK if the function is run by a different process.  Then one
process will have a preempt_count one larger than it should and one
would have a preempt_count one smaller.

The task with the one smaller preempt_count will probably cause a crash
when it preemptively reschedules erroneously.

In other words, you have:

	Process A		Process B
	preempt_count++
				preempt_count--

When both of those routines need to be done by the same process.

Also, you cannot use spin_lock_irqsave() in different functions at all
on sparc as it contains stack information.

	Robert Love