linux-kernel - handle_bad

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Message-ID: <CADtm3G4LRyojo+kX=neOsVYVX9_aY66yj-9XuFrjvrQcZJJYxg@mail.gmail.com>
Date:   Thu, 11 May 2017 16:21:23 -0700
From:   Gregory Fong <gregory.0xf0@...il.com>
To:     tglx@...utronix.de
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux@...linux.org.uk, Florian Fainelli <f.fainelli@...il.com>
Subject: handle_bad_irq and locking

Hi Thomas,

I noticed that when you changed arm irq handling to use the generic
implementation back in 2006 that you changed do_bad_IRQ() to the
following:

+#define do_bad_IRQ(irq,desc,regs)                      \
+do {                                                   \
+       spin_lock(&desc->lock);                         \
+       handle_bad_irq(irq, desc, regs);                \
+       spin_unlock(&desc->lock);                       \
+} while(0)

and it's mostly stayed the same since then.  As such, there are a few
examples of this being open-coded in the kernel in various irqchip
handlers such as that of drivers/irqchip/irq-brcmstb-l2.c, and even
more cases where the lock isn't being grabbed before calling
handle_bad_irq().

Since handle_bad_irq() is sort of a flow handler like
handle_edge_irq() etc., do you think it would make sense to do the
same as those and have it do the locking on its own?  A quick look
through existing users of handle_bad_irq() at [1] suggests that either
the locking isn't necessary or it's almost always done wrong.

Apologies if this has been asked before, but it's remarkably difficult
to search for.

[1] http://elixir.free-electrons.com/linux/latest/ident/handle_bad_irq

Thanks and regards,
Gregory