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 <t...@linutronix.de>
> Cc: Sebastian Andrzej Siewior <bige...@linutronix.de>
> Cc: Linus Walleij <linus.wall...@linaro.org>
> Signed-off-by: Julia Cartwright <ju...@ni.com>
Acked-by: Julia Lawall <julia.law...@lip6.fr>
> ---
> v1 -> v2:
> - Make use of 'exists' on match to find any codepath which acquires a lock.
> (via Julia Lawall)
> - Use 'when any' on '...' matches to loosen constraint (via Julia Lawall).
>
> .../coccinelle/locks/irq_chip_raw_spinlock.cocci | 96
> ++++++++++++++++++++++
> 1 file changed, 96 insertions(+)
> create mode 100644 scripts/coccinelle/locks/irq_chip_raw_spinlock.cocci
>
> diff --git a/scripts/coccinelle/locks/irq_chip_raw_spinlock.cocci
> b/scripts/coccinelle/locks/irq_chip_raw_spinlock.cocci
> new file mode 100644
> index 000000000000..0294831297d3
> --- /dev/null
> +++ b/scripts/coccinelle/locks/irq_chip_raw_spinlock.cocci
> @@ -0,0 +1,96 @@
> +// Copyright: (C) 2017 National Instruments Corp. GPLv2.
> +// Author: Julia Cartwright <ju...@ni.com>
> +//
> +// Identify callers of non-raw spinlock_t functions in hardirq irq_chip
> +// callbacks.
> +//
> +// spin_lock{_irq,_irqsave}(), w/ PREEMPT_RT are "sleeping" spinlocks, and so
> +// therefore "sleep" under contention; identify (and potentially patch)
> callers
> +// to use raw_spinlock_t instead.
> +//
> +// Confidence: Moderate
> +
> +virtual report
> +virtual patch
> +
> +@match@
> +identifier __irqchip;
> +identifier __irq_mask;
> +@@
> + static struct irq_chip __irqchip = {
> + .irq_mask = __irq_mask,
> + };
> +
> +@match2 depends on match exists@
> +identifier match.__irq_mask;
> +identifier data;
> +identifier x;
> +identifier l;
> +type T;
> +position j0;
> +expression flags;
> +@@
> + static void __irq_mask(struct irq_data *data)
> + {
> + ... when any
> + T *x;
> + ... when any
> +(
> + spin_lock_irqsave(&x->l@j0, flags);
> +|
> + spin_lock_irq(&x->l@j0);
> +|
> + spin_lock(&x->l@j0);
> +)
> + ... when any
> + }
> +
> +@match3 depends on match2 && patch@
> +type match2.T;
> +identifier match2.l;
> +@@
> + T {
> + ...
> +- spinlock_t l;
> ++ raw_spinlock_t l;
> + ...
> + };
> +
> +@match4 depends on match2 && patch@
> +type match2.T;
> +identifier match2.l;
> +expression flags;
> +T *x;
> +@@
> +
> +(
> +-spin_lock(&x->l)
> ++raw_spin_lock(&x->l)
> +|
> +-spin_lock_irqsave(&x->l, flags)
> ++raw_spin_lock_irqsave(&x->l, flags)
> +|
> +-spin_lock_irq(&x->l)
> ++raw_spin_lock_irq(&x->l)
> +|
> +-spin_unlock(&x->l)
> ++raw_spin_unlock(&x->l)
> +|
> +-spin_unlock_irq(&x->l)
> ++raw_spin_unlock_irq(&x->l)
> +|
> +-spin_unlock_irqrestore(&x->l, flags)
> ++raw_spin_unlock_irqrestore(&x->l, flags)
> +|
> +-spin_lock_init(&x->l)
> ++raw_spin_lock_init(&x->l)
> +)
> +
> +@script:python wat depends on match2 && report@
> +j0 << match2.j0;
> +t << match2.T;
> +l << match2.l;
> +@@
> +
> +msg = "Use of non-raw spinlock is illegal in this context (%s::%s)" % (t, l)
> +coccilib.report.print_report(j0[0], msg)
> --
> 2.12.0
>
>
