linux-kernel - MSI irqchip configured as IRQCHIP_ONESHOT

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Date:   Mon, 9 Dec 2019 12:27:22 +0200
From:   Ramon Fried <rfried.dev@...il.com>
To:     hkallweit1@...il.com, bhelgaas@...gle.com, marc.zyngier@....com,
        tglx@...utronix.de, lorenzo.pieralisi@....com
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: MSI irqchip configured as IRQCHIP_ONESHOT_SAFE causes spurious IRQs

Hi,
While debugging the root cause of spurious IRQ's on my PCIe MSI line it appears
that because of the line:
    info->chip->flags |= IRQCHIP_ONESHOT_SAFE;
in pci_msi_create_irq_domain()
The IRQF_ONESHOT is ignored, especially when requesting IRQ through
pci_request_threaded_irq() where handler is NULL.

The problem is that the MSI masking now only surrounds the HW handler,
and all additional MSI that occur before the threaded handler is
complete are considered by the note_interrupt() as spurious.

Besides the side effect of that, I don't really understand the logic
of not masking the MSI until the threaded handler is complete,
especially when there's no HW handler and only threaded handler.

Your thoughts?

Thank,
Ramon.