linux-kernel - Re: 2.6.19-rc6: known regressions (v4)

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Date:	Wed, 22 Nov 2006 09:28:16 -0800 (PST)
From:	Linus Torvalds <torvalds@...l.org>
To:	Pavel Emelianov <xemul@...nvz.org>
cc:	Morton Andrew Morton <akpm@...l.org>, mingo@...hat.com,
	Vivek Goyal <vgoyal@...ibm.com>, Adrian Bunk <bunk@...sta.de>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	dev@...ru
Subject: Re: 2.6.19-rc6: known regressions (v4)

On Wed, 22 Nov 2006, Pavel Emelianov wrote:
> 
> This works for me, but is this normal that desc's fields are
> modified non-atomically in note_interrupt()?

This is all inside the normal interrupt handling logic, so it should be 
exactly as safe as any interrupt is: we don't allow the _same_ interrupt 
to be entered recursively at the same time.

So yes, the counts etc are done non-atomically, but the code around it all 
guarantees that only one concurrent invocation happens per irq descriptor, 
so it's all ok.

(The one exception to that may be the "desc->status" modification in case 
the irq is determined to have screamed, since "status" can be modified by 
a recursive interrupt coming in, but (a) that's a "this irq is dead" 
schenario _anyway_ and (b) if we ever care, we should lock it _there_, not 
somewhere else).

			Linus
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