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Date:   Wed, 13 Mar 2019 18:21:13 -0500
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Jesse Hathaway <jesse@mbuki-mvuki.org>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org
Subject: Re: Regression causes a hang on boot with a Comtrol PCI card
Message-ID: <20190313232112.GC210027@google.com>
References: <CANSNSoWiKd98Dt1N2sSjP9Af8zk1NPV-=3P4VLtFs_cSQG4RUg@mail.gmail.com>
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Hi Jesse,

On Wed, Mar 13, 2019 at 11:50:07AM -0500, Jesse Hathaway wrote:
> Two regressions cause Linux to hang on boot when a Comtrol PCI card
> is present.
> 
> If I revert the following two commits, I can boot again and the card
> operates without issue:
> 
> 1302fcf0d03e (refs/bisect/bad) PCI: Configure *all* devices, not just
> hot-added ones
> 1c3c5eab1715 sched/core: Enable might_sleep() and smp_processor_id()
> checks early

I'm very sorry about the regression, but thank you very much for
narrowing it down and reporting it!

How did you narrow it down to *two* commits, and do you have to revert
both of them to avoid the hang?  Usually a bisection identifies a
single commit, and the two you mention aren't related.

> ; lspci -vs 82:00.0
> 82:00.0 Multiport serial controller: Comtrol Corporation Device 0061
>         Subsystem: Comtrol Corporation Device 0061
>         Flags: 66MHz, medium devsel, IRQ 35, NUMA node 1
>         Memory at c8004000 (32-bit, non-prefetchable) [size=4K]
>         Memory at c8000000 (32-bit, non-prefetchable) [size=16K]
>         Capabilities: [40] Hot-plug capable
>         Capabilities: [48] Power Management version 2
>         Kernel driver in use: rp2
>         Kernel modules: rp2
> 
> Is it possible that the problem is that the card claims to support
> Hot-plug, but does not?
> 
> I would love to help fix this issue, please let me know what other
> information would be helpful to provide.

Can you collect a complete dmesg log (with a working kernel) and
output of "sudo lspci -vvxxx"?  You can open a bug report at
https://bugzilla.kernel.org, attach the logs there, and respond here
with the URL.

Where does the hang happen?  Is it when we configure the Comtrol card?

Bjorn