linux-kernel - Re: [PATCH 1/2] PCI: mediatek-gen3: Stop acquiring spinlocks in {suspend,resume}

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Date:   Mon, 8 May 2023 09:44:13 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>, ryder.lee@...iatek.com
Cc:     jianjun.wang@...iatek.com, lpieralisi@...nel.org, kw@...ux.com,
        robh@...nel.org, bhelgaas@...gle.com, p.zabel@...gutronix.de,
        matthias.bgg@...il.com, linux-pci@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] PCI: mediatek-gen3: Stop acquiring spinlocks in
 {suspend,resume}_noirq

On 04.05.23 13:35, AngeloGioacchino Del Regno wrote:

Hi,

looking at your patch I am afraid there is an issue.

> In mtk_pcie_suspend_noirq() and mtk_pcie_resume_noirq() we are,
> respectively, disabling and enabling generation of interrupts and
> then saving and restoring the enabled interrupts register: since
> we're using noirq PM callbacks, that can be safely done without
> holding any spin lock.

Why? You can still race with another CPU in task context.
That is if you say that you do not need locking to touch
PCIE_INT_ENABLE_REG that is fine, but then why do you remove
it from one place only?
It is also touched in mtk_pcie_probe() at a minimum.

  
> That was noticed because of, and solves, the following issue:
> 
> <4>[   74.185982] ========================================================
> <4>[   74.192629] WARNING: possible irq lock inversion dependency detected
> <4>[   74.199276] 6.3.0-next-20230428+ #51 Tainted: G        W
> <4>[   74.205664] --------------------------------------------------------
> <4>[   74.212309] systemd-sleep/809 just changed the state of lock:
> <4>[   74.218347] ffff65a5c34c65a0 (&pcie->irq_lock){+...}-{2:2}, at: mtk_pcie_resume+0x50/0xa8
> <4>[   74.226870] but this lock was taken by another, HARDIRQ-safe lock in the past:
> <4>[   74.234389]  (&irq_desc_lock_class){-.-.}-{2:2}
> <4>[   74.234409]
> <4>[   74.234409]
> <4>[   74.234409] and interrupts could create inverse lock ordering between them.
> <4>[   74.234409]
> <4>[   74.251704]
> <4>[   74.251704] other info that might help us debug this:
> <4>[   74.258785]  Possible interrupt unsafe locking scenario:
> <4>[   74.258785]
> <4>[   74.266126]        CPU0                    CPU1
> <4>[   74.270942]        ----                    ----
> <4>[   74.275758]   lock(&pcie->irq_lock);

Lock A

> <4>[   74.279627]                                local_irq_disable();

strictly speaking irrelevant

> <4>[   74.285836]                                lock(&irq_desc_lock_class);

lock B

> <4>[   74.292667]                                lock(&pcie->irq_lock);

lock A

> <4>[   74.299061]   <Interrupt>

You do not need that interrupt.

> <4>[   74.301960]     lock(&irq_desc_lock_class);

lock B

> <4>[   74.306438]
> <4>[   74.306438]  *** DEADLOCK ***