Re: [BUG] Revert 0b05e2d671c4 'powerpc/32: cacheable_memcpy becomes memcpy'

[Michael Ellerman <mpe@ellerman.id.au>]

On Wed, 2015-09-16 at 21:54 -0400, Steven Rostedt wrote:
> On Wed, 16 Sep 2015 22:01:06 +0200 (CEST)
> Thomas Gleixner <tglx@linutronix.de> wrote:
> 
> > On Wed, 16 Sep 2015, Scott Wood wrote:
> > 
> > > On Wed, 2015-09-16 at 18:23 +0200, Thomas Gleixner wrote:
> > > > With this commit applied, my MPC5200 board fails to boot 4.3-rc1. The
> > > > boot failure is silent.
> > > > 
> > > > Bisection pointed straight to this commit. Reverting it on top of
> > > > 4.3-rc1 works like a charm.
> > > 
> > > Yes, we've been iterating on a fix for this, and I think the patches posted 
> > > earlier today are ready to go in:
> > > 
> > > http://patchwork.ozlabs.org/patch/518321/
> > > http://patchwork.ozlabs.org/patch/518323/
> > 
> > Tested-by: Thomas Gleixner <tglx@linutronix.de>
> > 
> > So now I have to chase down that one:
> > 
> > [    0.230210] ftrace: allocating 16560 entries in 49 pages
> > [    0.273313] ------------[ cut here ]------------
> > [    0.278048] WARNING: at /home/tglx/work/kernel/tip/tip/kernel/trace/ftrace.c:1974
> 
> OK, so this is where ftrace converts the mcount to nops.
> 
> Just to be clear, there's nothing in the command line that enables any
> function tracing, is there?
> 
> > [    0.285653] Modules linked in:
> > [    0.288781] CPU: 0 PID: 0 Comm: swapper Not tainted 4.2.0-50528-gfac33bf-dirty #29
> > [    0.296485] task: c06563e0 ti: c06a2000 task.ti: c06a2000
> > [    0.301976] NIP: c008df9c LR: c008e440 CTR: 00000000
> > [    0.307027] REGS: c06a3e80 TRAP: 0700   Not tainted  (4.2.0-50528-gfac33bf-dirty)
> > [    0.314631] MSR: 00021032 <ME,IR,DR,RI>  CR: 22028022  XER: 00000000
> > [    0.321126]
> > GPR00: 00000001 c06a3f30 c06563e0 ffffffea c3888c88 00000004 c06a3ef8 764d9364
> > GPR08: 00407584 c069df92 00000000 00000001 22022028 ffffffff 03fb9000 007fff00
> > GPR16: c065debc 00009032 c06b8aa0 c0011184 00000000 c06a711c 00000bb6 c38021a0
> > GPR24: 00000000 00008c88 00000bb6 c06a7120 c3888c88 101d6120 c3888c88 c00e1f2c
> > [    0.351444] NIP [c008df9c] ftrace_bug+0xbc/0x2d4
> > [    0.356160] LR [c008e440] ftrace_process_locs+0x28c/0x6cc
> > [    0.361652] Call Trace:
> > [    0.364169] [c06a3f30] [c00971a0] buffer_ftrace_now.isra.50+0x28/0x64 (unreliable)
> > [    0.371888] [c06a3f60] [c008e440] ftrace_process_locs+0x28c/0x6cc
> > [    0.378119] [c06a3fb0] [c0610848] ftrace_init+0xac/0x14c
> > [    0.383559] [c06a3fc0] [c06051fc] start_kernel+0x390/0x3a8
> > [    0.389147] [c06a3ff0] [00003438] 0x3438
> > [    0.393136] Instruction dump:
> > [    0.396154] 483f9951 3c60c059 7fe4fb78 3863b768 7fe5fb78 483f993d 41b20214 48000144
> > [    0.404060] 3d20c06a 3929df92 88090002 68000001 <0f000000> 2f800000 409e01b4 3d20c06a
> > [    0.412203] ---[ end trace dc8fa200cb88537f ]---
> > [    0.416912] ftrace failed to modify [<c00e1f2c>] change_protection+0x8/0x2c
> > [    0.424015]  actual: 74:66:74:70
> > [    0.427324] ftrace record flags: 0
> > [    0.430785]  (0)   expected tramp: c0011198
> > 
> > Happens somewhere between the powerpc merge and rc1. System boots up
> > to userspace and then locks hard ....
> 
> This could be a symptom and not the problem. What the above shows is
> that ftrace tried to convert the mcount at change_protection but what
> it expected was there wasn't. Unfortunately, it doesn't state exactly
> what it wants (that would take a arch specific function to do that, and
> this is in generic code). But what it found was "74 66 74 70", which I
> have no idea what type of command that is.

This is big endian, so I think that's:

  andis.  r6,r3,29808

Which is feasible.

Can you objdump the vmlinux? Mine looks like:

  c0157cf0 <change_protection>:
  c0157cf0:	7c 08 02 a6 	mflr    r0
  c0157cf4:	90 01 00 04 	stw     r0,4(r1)
  c0157cf8:	4b eb 9b f9 	bl      c00118f0 <_mcount>
  c0157d00:	7c 08 02 a6 	mflr    r0
  c0157d04:	7d 80 00 26 	mfcr    r12
  c0157d08:	90 01 00 64 	stw     r0,100(r1)
  c0157d0c:	bd c1 00 18 	stmw    r14,24(r1)
  c0157d10:	91 81 00 14 	stw     r12,20(r1)
  c0157d14:	81 23 00 28 	lwz     r9,40(r3)
  c0157d18:	75 2a 00 40 	andis.  r10,r9,64


cheers