linux-kernel - Re: [PATCH 08/32] genirq: Synchronize only with single thread on free

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Date:   Fri, 13 Jul 2018 09:21:09 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Keith Busch <keith.busch@...el.com>,
        Yinghai Lu <yinghai@...nel.org>, Sinan Kaya <okaya@...nel.org>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/32] genirq: Synchronize only with single thread on
 free_irq()

On Thu, Jul 12, 2018 at 05:21:09PM -0500, Bjorn Helgaas wrote:
> On Sat, Jun 16, 2018 at 09:25:00PM +0200, Lukas Wunner wrote:
> > When pciehp is converted to threaded IRQ handling, removal of unplugged
> > devices below a PCIe hotplug port happens synchronously in the IRQ
> > thread.  Removal of devices typically entails a call to free_irq() by
> > their drivers.
> > 
> > If those devices share their IRQ with the hotplug port, free_irq()
> > deadlocks because it calls synchronize_irq() to wait for all hard IRQ
> > handlers as well as all threads sharing the IRQ to finish.
> > 
> > Actually it's sufficient to wait only for the IRQ thread of the removed
> > device, so call synchronize_hardirq() to wait for all hard IRQ handlers
> > to finish, but no longer for any threads.  Compensate by rearranging the
> > control flow in irq_wait_for_interrupt() such that the device's thread
> > is allowed to run one last time after kthread_stop() has been called.
> 
> I assume this would need to be merged along with the rest of the
> series, which should probably go through the PCI tree, but I'm
> definitely not qualified to review this IRQ patch.  And it would need
> an ack from Thomas in any case.

A v2 of this patch has already been merged through the tip tree on June 24,
it's in linux-next as commit 519cc8652b3a, and ISTR that I marked this patch
either as "Obsoleted" or "Not Applicable" in pci-patchwork.  There was no
build-dependency of the succeeding patches in the series on this patch,
hence merging through a different tree was possible.

Thanks!

Lukas