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

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Date:	Tue, 3 Mar 2015 10:51:34 +0100
From:	Valentin Rothberg <Valentin.Rothberg@...6.fr>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, iss_storagedev@...com,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] block/cpqarray.c: remove IRQF_DISABLED flag

On Tue, Mar 3, 2015 at 9:37 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * 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.

I sent a patch that fixes that already.  See commit
b0e1ee8e1405ae033a0eac01ead275e65e4e6831 ("MSI-HOWTO.txt: remove
reference on IRQF_DISABLED").

> 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!

In the context of my PhD, I am diving a little into interrupt handling
in Linux.  I feel that a lot of information is scattered over
documentation, source code comments or no comments at all (i.e., the
code itself).  Currently I am writing a document (from hard IRQs to
workqueues).  As soon as it's finished I will think about how and
where it could be useful in documentation.

Kind regards,
 Valentin

> Thanks,
>
>         Ingo
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