linux-kernel - Re: [PATCH v4] irqchip/ls-extirq: fix invalid wait context by avoiding to use regmap

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Message-ID: <501b52ba-7691-0263-c007-38174c7e5c22@seco.com>
Date:   Thu, 28 Jul 2022 11:25:23 -0400
From:   Sean Anderson <sean.anderson@...o.com>
To:     Vladimir Oltean <vladimir.oltean@....com>,
        linux-kernel@...r.kernel.org
Cc:     Lee Jones <lee.jones@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Arnd Bergmann <arnd@...db.de>,
        Hou Zhiqiang <Zhiqiang.Hou@....com>,
        Biwen Li <biwen.li@....com>
Subject: Re: [PATCH v4] irqchip/ls-extirq: fix invalid wait context by
 avoiding to use regmap



On 7/28/22 10:42 AM, Vladimir Oltean wrote:
> The irqchip->irq_set_type method is called by __irq_set_trigger() under
> the desc->lock raw spinlock.
> 
> The ls-extirq implementation, ls_extirq_irq_set_type(), uses an MMIO
> regmap created by of_syscon_register(), which uses plain spinlocks
> (the kind that are sleepable on RT).
> 
> Therefore, this is an invalid locking scheme for which we get a kernel
> splat stating just that ("[ BUG: Invalid wait context ]"), because the
> context in which the plain spinlock may sleep is atomic due to the raw
> spinlock. We need to go raw spinlocks all the way.

Could we just use use_raw_spinlock in the regmap config?

--Sean

> Make this driver ioremap its INTPCR register on its own, and stop
> relying on syscon to provide a regmap. Since the regmap we got from
> syscon belonged to the parent and the newly ioremapped region belongs
> just to us, the offset to the INTPCR register is now 0, because of the
> address translation that takes place through the device tree.
> 
> One complication, due to the fact that this driver uses IRQCHIP_DECLARE
> rather than traditional platform devices with probe and remove methods,
> is that we cannot use devres, so we need to implement a full-blown
> cleanup procedure on the error path.
> 
> Fixes: 0dcd9f872769 ("irqchip: Add support for Layerscape external interrupt lines")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---