Hi Alessio,

Le 26/08/2016 à 04:32, Scott Wood a écrit :

On Tue, 2016-08-23 at 13:34 +0200, Christophe Leroy wrote:

quoted

Le 23/08/2016 à 11:20, Alessio Igor Bogani a écrit :

quoted

Hi Christophe,

Sorry for delay in reply I was on vacation.

On 6 August 2016 at 11:29, christophe leroy [off-list ref]
wrote:

quoted

Alessio,


Le 05/08/2016 à 09:51, Christophe Leroy a écrit :

quoted

Le 19/07/2016 à 23:52, Scott Wood a écrit :

quoted

On Tue, 2016-07-19 at 12:00 +0200, Alessio Igor Bogani wrote:

quoted

Hi all,

I have got two boards MVME5100 (MPC7410 cpu) and MVME7100
(MPC8641D
cpu) for which I use the same cross-compiler (ppc7400).

I tested these against kernel HEAD to found that these don't boot
anymore (PID 1 crash).

Bisecting results in first offending commit:
7aef4136566b0539a1a98391181e188905e33401

Removing it from HEAD make boards boot properly again.

A third system based on P2010 isn't affected at all.

Is it a regression or I have made something wrong?

I booted both my next branch, and Linus's master on MPC8641HPCN and
didn't see
this -- though possibly your RFS is doing something
different.  Maybe
that's
the difference with P2010 as well.

Is there any way you can debug the cause of the crash?  Or send me a
minimal
RFS that demonstrates the problem (ideally with debug symbols on the
userspace
binaries)?

I got from Alessio the below information:

systemd[1]: Caught <BUS>, core dump failed (child 137, code=killed,
status=7/BUS).
systemd[1]: Freezing execution.


What can generate SIGBUS ?
And shouldn't we also get some KERN_ERR trace, something like
"unhandled
signal 7 at ....." ?

As far as I can see, SIGBUS is mainly generated from alignment
exception.
According to 7410 Reference Manual, alignment exception can happen in
the
following cases:
* An operand of a dcbz instruction is on a page that is write-through or
cache-inhibited for a virtual mode access.
* An attempt to execute a dcbz instruction occurs when the cache is
disabled
or locked.

Could try with below patch to check if the dcbz insn is causing the
SIGBUS ?

Unfortunately that patch doesn't solve the problem.

Is there a chance that cache behavior could settled by board firmware
(PPCBug on the MPC7410 board and MotLoad on the MPC8641D one)?
In that case what do you suggest me to looking for?

If the removal of dcbz doesn't solve the issue, I don't think it is a
cache related issue.
As far as I understood, your init gets a SIGBUS signal, right ? Then we
must identify the reason for that sigbus.

My guess would be errors demand-loading a page via NFS.

One approach might be to hack up the code so that both versions of
csum_partial_copy_generic() are present, and call both each time.  If the
results differ or the copied bytes are wrong, then spit out a dump of the
details.

Can you try the patch below ? I have identified that in case the packet 
is smaller than a cacheline, it doesn't get cache-aligned so the result 
shall not be rotated in case of odd dest address.

This patch goes in addition to the previous fix (1bc8b816cb805) as it 
fixes a different case.

Christophe

diff --git a/arch/powerpc/lib/checksum_32.S b/arch/powerpc/lib/checksum_32.S
index 68f6862..3971cfb 100644
--- a/arch/powerpc/lib/checksum_32.S
+++ b/arch/powerpc/lib/checksum_32.S

@@ -127,18 +127,19 @@ _GLOBAL(csum_partial_copy_generic)
  	stw	r7,12(r1)
  	stw	r8,8(r1)

-	rlwinm	r0,r4,3,0x8
-	rlwnm	r6,r6,r0,0,31	/* odd destination address: rotate one byte */
-	cmplwi	cr7,r0,0	/* is destination address even ? */
  	addic	r12,r6,0
  	addi	r6,r4,-4
  	neg	r0,r4
  	addi	r4,r3,-4
  	andi.	r0,r0,CACHELINE_MASK	/* # bytes to start of cache line */
+	crset	4*cr7+eq
  	beq	58f

  	cmplw	0,r5,r0			/* is this more than total to do? */
  	blt	63f			/* if not much to do */
+	rlwinm	r7,r6,3,0x8
+	rlwnm	r12,r12,r7,0,31	/* odd destination address: rotate one byte */
+	cmplwi	cr7,r7,0	/* is destination address even ? */
  	andi.	r8,r0,3			/* get it word-aligned first */
  	mtctr	r8
  	beq+	61f

--