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SubjectRe: Regression in 4.11 - PowerPC crashes on boot, bisected to commit 5657933dbb6e
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On 03/06/2017 03:48 PM, Benjamin Herrenschmidt wrote:
> On Mon, 2017-03-06 at 13:46 -0600, Larry Finger wrote:
>> I was able to create a PPC emulation with debian-8.7.1-powerpc-CD-1.iso
>>> following the instructions in https://gmplib.org/~tege/qemu.html. My only
>> problem was that "-net tap" fails and I did not find any way to get networking
>> working.
>>
>> After looking at the screen through a number of crashes, I have determined that
>> the top entry in the traceback comes from dmam_alloc_coherent(). I have not been
>> able to see the offset to determine which BUG_ON call in that routine is being
>> triggered.
>>
>> I tried to modify panic() to see if I could keep the screen on longer after the
>> failure, but no joy so far.
>
> I think the problem is this code in drivers/macintosh/macio_asic.c:
>
> #ifdef CONFIG_PCI
> /* Set the DMA ops to the ones from the PCI device, this could be
> * fishy if we didn't know that on PowerMac it's always direct ops
> * or iommu ops that will work fine
> *
> * To get all the fields, copy all archdata
> */
> dev->ofdev.dev.archdata = chip->lbus.pdev->dev.archdata;
> #endif /* CONFIG_PCI */
>
> This is definitely bad. A quick fix is to copy the new dev->dma_ops field
> (as well, there is still stuff in archdata that we need too).
>
> A better long term fix is to have a set of macio_dma_ops wrappers that do
> "the right thing".

Ben,

Attached is a patch that fixes the crash. At the moment, it has my s-o-b, but I
do not feel it right to claim authorship. My role should be a
Reported-and-tested-by. Please advise.

Larry


From fe51bd0233e10d0eed64cfe177f5d43ca95642a7 Mon Sep 17 00:00:00 2001
From: Larry Finger <Larry.Finger@lwfinger.net>
Date: Thu, 9 Mar 2017 16:06:21 -0600
Subject: [PATCH] powerpc: Fix crash introduced with commit 5657933dbb6e

Code inserted during the git merges before kernel 4.11-rc1 caused an
early panic quickly followed by a complete shutdown. The traceback was
not displayed long enough to read or photograph.

The problem was bisected to commit 5657933dbb6e ("treewide: Move dma_ops
from struct dev_archdata into struct device"). The problem was a missing
copy of critical information from struct dev_archdata into struct device,
leading to the dereference of a null pointer.

Fixes: commit 5657933dbb6e ("treewide: Move dma_ops from struct dev_archdata into struct device")
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
---
drivers/macintosh/macio_asic.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/drivers/macintosh/macio_asic.c b/drivers/macintosh/macio_asic.c
index 3f041b1..f757cef2 100644
--- a/drivers/macintosh/macio_asic.c
+++ b/drivers/macintosh/macio_asic.c
@@ -392,6 +392,7 @@ static struct macio_dev * macio_add_one_device(struct macio_chip *chip,
* To get all the fields, copy all archdata
*/
dev->ofdev.dev.archdata = chip->lbus.pdev->dev.archdata;
+ dev->ofdev.dev.dma_ops = chip->lbus.pdev->dev.dma_ops;
#endif /* CONFIG_PCI */

#ifdef DEBUG
--
2.10.2
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