linux-kernel - Re: [PATCH v2 1/9] Coccinelle: locks: identify callers of spin_lock{,_irq,

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Date:   Wed, 22 Mar 2017 22:45:25 +0100 (CET)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Julia Cartwright <julia@...com>
cc:     Julia Lawall <julia.lawall@...6.fr>,
        Gilles Muller <Gilles.Muller@...6.fr>,
        Nicolas Palix <nicolas.palix@...g.fr>,
        Michal Marek <mmarek@...e.com>, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Linus Walleij <linus.walleij@...aro.org>, cocci@...teme.lip6.fr
Subject: Re: [PATCH v2 1/9] Coccinelle: locks: identify callers of
 spin_lock{,_irq,_irqsave}() in irqchip implementations



On Wed, 22 Mar 2017, Julia Cartwright wrote:

> On Wed, Mar 22, 2017 at 10:54:15AM +0100, Julia Lawall wrote:
> > On Tue, 21 Mar 2017, Julia Cartwright wrote:
> > > On PREEMPT_RT, the spinlock_t type becomes an object which sleeps under
> > > contention.  The codepaths used to support scheduling (irq dispatching, arch
> > > code, the scheduler, timers) therefore must make use of the
> > > raw_spin_lock{,_irq,_irqsave}() variations which preserve the non-sleeping
> > > spinlock behavior.
> > >
> > > Because the irq_chip callbacks are invoked in the process of interrupt
> > > dispatch, they cannot therefore make use of spin_lock_t type.  Instead, the
> > > usage of raw_spinlock_t is appropriate.
> > >
> > > Provide a spatch to identify (and attempt to patch) such problematic irqchip
> > > implementations.
> > >
> > > Note to those generating patches using this spatch; in order to maintain
> > > correct semantics w/ PREEMPT_RT, it is necessary to audit the
> > > raw_spinlock_t-protected codepaths to ensure their execution is bounded and
> > > minimal.  This is a manual audit process.
> > >
> > > See commit 47b03ca903fb0 ("pinctrl: qcom: Use raw spinlock variants") as an
> > > example of _one_ such instance, which fixed a real bug seen in the field.
> > >
> > > Cc: Thomas Gleixner <tglx@...utronix.de>
> > > Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> > > Cc: Linus Walleij <linus.walleij@...aro.org>
> > > Signed-off-by: Julia Cartwright <julia@...com>
> >
> > Acked-by: Julia Lawall <julia.lawall@...6.fr>
>
> Thanks, Julia.
>
> How do these semantic patches normally land?  It looks like they quite a
> few have gone through the kbuild tree, is this the norm?

Michal Marek takes care of them.

julia

>
> Thanks,
>    Other Julia
>