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

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Message-ID: <20180713114411.GI28466@bhelgaas-glaptop.roam.corp.google.com>
Date:   Fri, 13 Jul 2018 06:44:11 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Lukas Wunner <lukas@...ner.de>
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 Fri, Jul 13, 2018 at 09:21:09AM +0200, Lukas Wunner wrote:
> 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.

Perfect, thanks!