On 09/21/2017 11:44 AM, Christophe LEROY wrote:
Le 20/09/2017 à 05:45, Guenter Roeck a écrit :
On 09/19/2017 08:05 PM, Michael Ellerman wrote:
Guenter Roeck <li...@roeck-us.net> writes:
Hi,
I see a the following traceback when running an SMP image based on
85xx/mpc85xx_cds_defconfig in qemu.
------------[ cut here ]------------
WARNING: CPU: 0 PID: 1 at kernel/smp.c:416 smp_call_function_many+0xcc/0x2fc
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.14.0-rc1-00009-g0666f56 #1
task: cf830000 task.stack: cf82e000
NIP: c00a93c8 LR: c00a9634 CTR: 00000001
REGS: cf82fde0 TRAP: 0700 Not tainted (4.14.0-rc1-00009-g0666f56)
MSR: 00021000 <CE,ME> CR: 24000082 XER: 00000000
GPR00: c00a9634 cf82fe90 cf830000 c050ad3c c0015a54 00000000 00000001 00000001
GPR08: 00000001 00000000 00000000 cf82e000 24000084 00000000 c0003150 00000000
GPR16: 00000000 00000000 00000000 00000000 00000000 00000001 00000000 c0510000
GPR24: 00000000 c0015a54 00000000 c050ad3c c051823c c050ad3c 00000025 00000000
NIP [c00a93c8] smp_call_function_many+0xcc/0x2fc
LR [c00a9634] smp_call_function+0x3c/0x50
Call Trace:
[cf82fe90] [00000010] 0x10 (unreliable)
[cf82fed0] [c00a9634] smp_call_function+0x3c/0x50
[cf82fee0] [c0015d2c] flush_tlb_kernel_range+0x20/0x38
[cf82fef0] [c001524c] mark_initmem_nx+0x154/0x16c
[cf82ff20] [c001484c] free_initmem+0x20/0x4c
[cf82ff30] [c000316c] kernel_init+0x1c/0x108
[cf82ff40] [c000f3a8] ret_from_kernel_thread+0x5c/0x64
Instruction dump:
7c0803a6 7d808120 38210040 4e800020 3d20c052 812981a0 2f890000 40beffac
3d20c051 8929ac64 2f890000 40beff9c <0fe00000> 4bffff94 7fc3f378 7f64db78
---[ end trace 7da7bdcf8b15ddb3 ]---
Thanks.
I guess the system still runs OK otherwise, you're just seeing the warning?
Yes, though I am not sure if that is because there is only one active CPU
(there is
still only one if I say "-smp 4" on the qemu command line).
A complete log is available at:
http://kerneltests.org/builders/qemu-ppc-master/builds/814/steps/qemubuildcommand/logs/stdio
Bisect points to commit 3184cc4b6f6a1dc0 ("powerpc/mm: Fix kernel RAM protection
after freeing unused memory on PPC32"). Bisect log is attached. A quick look
suggests that mark_initmem_nx() is called with interrupts disabled, which
triggers the traceback.
Hmm. Yes the MSR says you have interrupts disabled (EE missing).
But I don't see why. start_kernel() did local_irq_enable(), so I don't
understand why we got to mark_initmem_nx() with them disabled. I'll hope
that Christophe has some idea.
Good question. I only see this with one of 9 ppc emulations, with
85xx/mpc85xx_cds_defconfig
+CONFIG_DEVTMPFS=y +CONFIG_SMP=y. Maybe there is a platform specific init
function
which leaves interrupts disabled. Question is which one that might be.
Unfortunatly no, I have no idea. My three platforms (860, 885 and 8321) are not
SMPs so that warning would not appear, but I added a WARN_ON(1) just become
calling mark_initmem_nx(), and I can confirm that MSR has EE set on all three
at that time.
You should still be able to compile and run a SMP kernel. mpc85xx_cds_defconfig
without CONFIG_SMP=y does not show the warning either.
Turns out interrupts are disabled in change_page_attr(), called by
mark_initmem_nx().
change_page_attr() calls flush_tlb_kernel_range() with interrupts disabled.
This only happens if CONFIG_PPC_MMU_NOHASH=y.
Given that, I would assume that this will be seen with every 32 bit ppc build
which has
CONFIG_SMP=y and CONFIG_PPC_MMU_NOHASH=y.
Maybe the problem was really introduced with commit e611939fc8ec1 ("powerpc/mm:
Ensure
change_page_attr() doesn't invalidate pinned TLBs"). From the context it
appears that
flush_tlb_kernel_range() should not be called with interrupts disabled.
Indeed, moving flush_tlb_kernel_range() outside the irq disabled code fixes
the problem for me.
Thanks,
Guenter
So as you suggest, there must be a platform specific stuff leaving the
interrupts disabled.
Christophe
Guenter
