linux-kernel - Re: Generic kernel fails to boot on Alpha bisected to b38d08f3181c

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Message-ID: <20181213160724.GU2509588@devbig004.ftw2.facebook.com>
Date:   Thu, 13 Dec 2018 08:07:24 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Michael Cree <mcree@...on.net.nz>, linux-alpha@...r.kernel.org,
        linux-kernel@...r.kernel.org, debian-alpha@...ts.debian.org
Subject: Re: Generic kernel fails to boot on Alpha bisected to b38d08f3181c

Hello, Michael.

On Thu, Dec 13, 2018 at 09:26:12PM +1300, Michael Cree wrote:
> A kernel built for generic UP Alpha had been noted to fail to boot
> for quite some time (since the release of 3.18).  The kernel either
> locks up before printing any messages to the console or just falls
> back into the SRM with a HALT instruction again before any messages
> are printed to the console.  A work around is to either use a kernel
> built for generic SMP or to build a machine specific kernel as these
> boot correctly.
> 
> Because there were other compile errors at the time it proved
> difficult to bisect, but we are continuing to get complaints about
> it as it renders the Debian Alpha installer somewhat useless, so I
> returned to trying to find the problem and managed to bisect it to:
> 
> commit b38d08f3181c5025a7ce84646494cc4748492a3b
> Author: Tejun Heo <tj@...nel.org>
> Date:   Tue Sep 2 14:46:02 2014 -0400
> 
>     percpu: restructure locking
> 
> Any suggestions as to what might be the problem and a fix?

So, the only thing I can think of is that it's calling
spin_unlock_irq() while irq handling isn't set up yet.  Can you please
try the followings?

1. Convert all spin_[un]lock_irq() to
   spin_lock_irqsave/unlock_irqrestore().

2. If that still doesn't work, just convert all of them to
   spin_lock/unlock(), which is obviously broken but still is useful
   for debugging.

Thanks.

-- 
tejun