linux-kernel - Re: [PATCH] block/cpqarray.c: remove IRQF

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Date:	Tue, 3 Mar 2015 09:37:53 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Valentin Rothberg <Valentin.Rothberg@...6.fr>,
	iss_storagedev@...com, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] block/cpqarray.c: remove IRQF_DISABLED flag


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Fri, 27 Feb 2015 13:32:55 +0100 Valentin Rothberg <Valentin.Rothberg@...6.fr> wrote:
> 
> > The IRQF_DISABLED is a NOOP and scheduled to be removed.  According to
> > Ingo Molnar (e58aa3d2d0cc01ad8d6f7f640a0670433f794922) running IRQ
> > handlers with interrupts enabled can cause stack overflows when the
> > interrupt line of the issuing device is still active.
> > 
> 
> I suggest you prepare a patch which removes IRQF_DISABLED entirely. 

Yes.

> Several drivers still use it and it is possible that they have been 
> buggy for some time, [...]

Well, IRQF_DISABLED is now the unconditional default, so requesting 
irqs with IRQF_DISABLED is simply superfluous, not buggy, AFAICS.

> [...] so we should be careful to cc the relevant maintainers (they 
> probably don't exist) so they can check out what's going on in their 
> code.

I think part of it might be the stale spinlock related comment in 
Documentation/PCI/MSI-HOWTO.txt which explicitly recommends 
IRQF_DISABLED use. So that reference should be zapped as well.

So maybe drivers still using IRQF_DISABLED might not be potentially 
broken drivers at all, but are drivers written by exceptionally 
capable driver authors, who read kernel documentation!

Thanks,

	Ingo
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