Generic kernel fails to boot on Alpha bisected to b38d08f3181c

Generic kernel fails to boot on Alpha bisected to b38d08f3181c

[Michael Cree]

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@kernel.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?

Cheers,
Michael.

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

[Tejun Heo]

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@kernel.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

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

[Michael Cree]

[-- Attachment #1: Type: text/plain, Size: 1446 bytes --]

On Thu, Dec 13, 2018 at 08:07:24AM -0800, Tejun Heo wrote:
> 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@kernel.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().

Yes, that's it.  With the attached patch the kernel boots.

Cheers
Michael.

[-- Attachment #2: 0001-percpu-convert-spin_lock_irq-to-spin_lock_irqsave.patch --]
[-- Type: text/x-diff, Size: 1541 bytes --]

From e08cf3c714184d8fe168fffcd7d15732924deb1e Mon Sep 17 00:00:00 2001
From: Michael Cree <mcree@orcon.net.nz>
Date: Fri, 14 Dec 2018 17:24:31 +1300
Subject: [PATCH] percpu: convert spin_lock_irq to spin_lock_irqsave.

Bisection lead to commit b38d08f3181c ("percpu: restructure
locking") as being the cause of lockups at initial boot on
the kernel built for generic Alpha.

On a suggestion by Tejun Heo that:

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().
---
 mm/percpu-km.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/percpu-km.c b/mm/percpu-km.c
index 38de70ab1a0d..0f643dc2dc65 100644
--- a/mm/percpu-km.c
+++ b/mm/percpu-km.c
@@ -50,6 +50,7 @@ static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp)
 	const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
 	struct pcpu_chunk *chunk;
 	struct page *pages;
+	unsigned long flags;
 	int i;
 
 	chunk = pcpu_alloc_chunk(gfp);
@@ -68,9 +69,9 @@ static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp)
 	chunk->data = pages;
 	chunk->base_addr = page_address(pages) - pcpu_group_offsets[0];
 
-	spin_lock_irq(&pcpu_lock);
+	spin_lock_irqsave(&pcpu_lock, flags);
 	pcpu_chunk_populated(chunk, 0, nr_pages, false);
-	spin_unlock_irq(&pcpu_lock);
+	spin_unlock_irqrestore(&pcpu_lock, flags);
 
 	pcpu_stats_chunk_alloc();
 	trace_percpu_create_chunk(chunk->base_addr);
-- 
2.11.0