linux-kernel - Re: [PATCH v2] PCI/MSI: Avoid torn updates to MSI pairs

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Date:   Wed, 29 Jan 2020 10:00:59 -0800
From:   Evan Green <evgreen@...omium.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Rajat Jain <rajatja@...gle.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-pci <linux-pci@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        x86@...nel.org, Marc Zyngier <maz@...nel.org>
Subject: Re: [PATCH v2] PCI/MSI: Avoid torn updates to MSI pairs

On Tue, Jan 28, 2020 at 2:48 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> Evan,
>
> Evan Green <evgreen@...omium.org> writes:
> > On Tue, Jan 28, 2020 at 6:38 AM Thomas Gleixner <tglx@...utronix.de> wrote:
> >> The patch is only lightly tested, but so far it survived.
> >>
> >
> > Hi Thomas,
> > Thanks for the patch, I gave it a try. I get the following splat, then a hang:
> >
> > [   62.238406]        CPU0
> > [   62.241135]        ----
> > [   62.243863]   lock(vector_lock);
> > [   62.247467]   lock(vector_lock);
> > [   62.251071]
> > [   62.251071]  *** DEADLOCK ***
> > [   62.251071]
> > [   62.257687]  May be due to missing lock nesting notation
> > [   62.257687]
> > [   62.265274] 2 locks held by migration/1/17:
> > [   62.269946]  #0: 00000000cfa9d8c3 (&irq_desc_lock_class){-.-.}, at:
> > irq_migrate_all_off_this_cpu+0x44/0x28f
> > [   62.280846]  #1: 000000006885da2d (vector_lock){-.-.}, at:
> > msi_set_affinity+0x13c/0x27b
> > [   62.289801]
> > [   62.289801] stack backtrace:
> > [   62.294669] CPU: 1 PID: 17 Comm: migration/1 Not tainted 4.19.96 #2
> > [   62.310713] Call Trace:
> > [   62.313446]  dump_stack+0xac/0x11e
> > [   62.317255]  __lock_acquire+0x64f/0x19bc
> > [   62.321646]  ? find_held_lock+0x3d/0xb8
> > [   62.325936]  ? pci_conf1_write+0x4f/0xdf
> > [   62.330320]  lock_acquire+0x1b2/0x1fa
> > [   62.334413]  ? apic_retrigger_irq+0x31/0x63
> > [   62.339097]  _raw_spin_lock_irqsave+0x51/0x7d
> > [   62.343972]  ? apic_retrigger_irq+0x31/0x63
> > [   62.348646]  apic_retrigger_irq+0x31/0x63
> > [   62.353124]  msi_set_affinity+0x25a/0x27b
>
> Bah. I'm sure I looked at that call chain, noticed the double vector
> lock and then forgot. Delta patch below.

It's working well with the delta patch, been running for about an hour
with no issues.
-Evan