Run 'usermode-agent' cause kernel panic on Powerpc

DISCUSSION xufeng zhang 3 participants 4 messages Dec 7, 2010 – Dec 9, 2010 PowerPC

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xufeng zhang

author

2010-12-07 06:48 UTC #0 lore raw

Hi Dave,

I have a question with the below patch you made before:
----------------------------------------
powerpc/booke: Add support for advanced debug registers

From: Dave Kleikamp <[email protected]>

Based on patches originally written by Torez Smith.
-----------------------------------------

I meet a kernel panic problem while running 'usermode-agent' on PowerPC
----------------------------------------

Oops: Exception in kernel mode, sig: 5 [#1]
PREEMPT LTT NESTING LEVEL : 0
MPC8536 DS
last sysfs file: /sys/devices/f3000000.soc/f3003100.i2c/i2c-1/i2c-dev/i2c-1/dev
Modules linked in:
NIP: c00081a0 LR: c03a9560 CTR: c003547c
REGS: ef11bf10 TRAP: 2002   Not tainted  (2.6.34.6-WR4.0.0.0_standard)
MSR: 00021000 <ME,CE>  CR: 44000624  XER: 00000000

TASK = efc1de00[752] 'usermode-agent' THREAD: ef63e000
GPR00: cc00cc00 ef63fe60 efc1de00 efc1de00 efc1f700 c04c8000 00258560 ffffffff
GPR08: ffda8a00 40000000 00001fda c0500000 49eaebbd 1008b654 3ff8a900 00000000
GPR16: 00000000 eed84c40 c03b4570 c04ee4d0 c04ca870 ef63e03c 00000000 00000000
GPR24: c04f7ee8 c04ee4c0 00000004 c04ca440 ef63e000 efc1f700 c04ca440 efc1de00 NIP [c00081a0] __switch_to+0xac/0x104
LR [c03a9560] schedule+0x20c/0x3f4

Call Trace:

[ef63fe60] [efc1f700] 0xefc1f700 (unreliable)
[ef63fe70] [c03a9560] schedule+0x20c/0x3f4
[ef63fec0] [c00429e0] do_wait+0x1a4/0x278
[ef63fef0] [c0042b44] sys_wait4+0x90/0xf8
[ef63ff40] [c00106d4] ret_from_syscall+0x0/0x4
------------------------------------------

Actually, this problem is caused by enabling On Chip Debugging, when On Chip Debugging is enabled, we enable MSR_DE as below:
#define MSR_KERNEL (MSR_ME|MSR_RI|MSR_CE|MSR_DE)

If I comment out "mtspr(SPRN_DBCR0, thread->dbcr0);" in prime_debug_regs() function, then it will be ok.

Here is my analysis for this problem:
Run 'usermode-agent' application will set Internal Debug Mode(IDM) and Instruction Complete Debug Event(ICMP)flags for thread.
As MSR_DE is enabled, when execute context switching in prime_debug_regs(), thread->dbcr0 would write to SPRN_DBCR0 register.
So this will enable Instruction Complete Debug Event interrupt, and it will cause a kernel-mode exception right now, it will be handled in native_DebugException(), then kernel detected this exception not happens in user-mode, lastly kernel call die() and kill current process.

So my question is could I just comment out "mtspr(SPRN_DBCR0, thread->dbcr0);" in prime_debug_regs()? I'm sure whether or not it will impose a bad impact on debugging.
Thanks in advance!

Thanks,
Xufeng Zhang

Dave Kleikamp

2010-12-07 14:04 UTC #1 lore raw

Quoted 61 lines · xufeng zhang

Hi Dave,
I have a question with the below patch you made before:
----------------------------------------
powerpc/booke: Add support for advanced debug registers
From: Dave Kleikamp <[email protected]>
Based on patches originally written by Torez Smith.
-----------------------------------------
I meet a kernel panic problem while running 'usermode-agent' on PowerPC
----------------------------------------
Oops: Exception in kernel mode, sig: 5 [#1]
PREEMPT LTT NESTING LEVEL : 0
MPC8536 DS
last sysfs file:
/sys/devices/f3000000.soc/f3003100.i2c/i2c-1/i2c-dev/i2c-1/dev
Modules linked in:
NIP: c00081a0 LR: c03a9560 CTR: c003547c
REGS: ef11bf10 TRAP: 2002   Not tainted  (2.6.34.6-WR4.0.0.0_standard)
MSR: 00021000 <ME,CE>  CR: 44000624  XER: 00000000
TASK = efc1de00[752] 'usermode-agent' THREAD: ef63e000
GPR00: cc00cc00 ef63fe60 efc1de00 efc1de00 efc1f700 c04c8000 00258560 ffffffff
GPR08: ffda8a00 40000000 00001fda c0500000 49eaebbd 1008b654 3ff8a900 00000000
GPR16: 00000000 eed84c40 c03b4570 c04ee4d0 c04ca870 ef63e03c 00000000 00000000
GPR24: c04f7ee8 c04ee4c0 00000004 c04ca440 ef63e000 efc1f700 c04ca440 efc1de00
NIP [c00081a0] __switch_to+0xac/0x104
LR [c03a9560] schedule+0x20c/0x3f4
Call Trace:
[ef63fe60] [efc1f700] 0xefc1f700 (unreliable)
[ef63fe70] [c03a9560] schedule+0x20c/0x3f4
[ef63fec0] [c00429e0] do_wait+0x1a4/0x278
[ef63fef0] [c0042b44] sys_wait4+0x90/0xf8
[ef63ff40] [c00106d4] ret_from_syscall+0x0/0x4
------------------------------------------
Actually, this problem is caused by enabling On Chip Debugging, when On Chip Debugging is enabled, we enable MSR_DE as below:
#define MSR_KERNEL (MSR_ME|MSR_RI|MSR_CE|MSR_DE)
If I comment out "mtspr(SPRN_DBCR0, thread->dbcr0);" in prime_debug_regs() function,
then it will be ok.
Here is my analysis for this problem:
Run 'usermode-agent' application will set Internal Debug Mode(IDM) and Instruction Complete Debug Event(ICMP)flags for thread.
As MSR_DE is enabled, when execute context switching in prime_debug_regs(), thread->dbcr0 would write to SPRN_DBCR0 register.
So this will enable Instruction Complete Debug Event interrupt, and it will cause a kernel-mode
exception right now, it will be handled in native_DebugException(), then kernel detected
this exception not happens in user-mode, lastly kernel call die() and kill current process.

Quoted 3 lines

So my question is could I just comment out "mtspr(SPRN_DBCR0, thread->dbcr0);" in prime_debug_regs()?
I'm sure whether or not it will impose a bad impact on debugging.

I believe it would have such an impact. I don't see that user-mode debugging would be enabled at all.

Maybe something like this untested patch:

arch/powerpc/kernel/process.c +7 -0

index 84906d3..0e7d1cf 100644
@@ -323,6 +323,13 @@ static void set_debug_reg_defaults(struct thread_struct *thread)
 
 static void prime_debug_regs(struct thread_struct *thread)
 {
+	/*
+	 * If we're setting up debug events for user space, make sure they
+	 * don't fire in kernel space before we get to user space
+	 */
+	if (thread->dbcr0 & DBCR0_IDM)
+		mtmsr(mfmsr() & ~MSR_DE);
+
 	mtspr(SPRN_IAC1, thread->iac1);
 	mtspr(SPRN_IAC2, thread->iac2);
 #if CONFIG_PPC_ADV_DEBUG_IACS > 2

Signature · 2 lines

Dave Kleikamp
IBM Linux Technology Center

xufeng zhang

author

2010-12-08 01:20 UTC #2 lore raw

Quoted 82 lines · Dave Kleikamp

Quoted 61 lines · xufeng zhang
Hi Dave,
I have a question with the below patch you made before:
----------------------------------------
powerpc/booke: Add support for advanced debug registers
From: Dave Kleikamp<[email protected]>
Based on patches originally written by Torez Smith.
-----------------------------------------
I meet a kernel panic problem while running 'usermode-agent' on PowerPC
----------------------------------------
Oops: Exception in kernel mode, sig: 5 [#1]
PREEMPT LTT NESTING LEVEL : 0
MPC8536 DS
last sysfs file:
/sys/devices/f3000000.soc/f3003100.i2c/i2c-1/i2c-dev/i2c-1/dev
Modules linked in:
NIP: c00081a0 LR: c03a9560 CTR: c003547c
REGS: ef11bf10 TRAP: 2002   Not tainted  (2.6.34.6-WR4.0.0.0_standard)
MSR: 00021000<ME,CE>   CR: 44000624  XER: 00000000
TASK = efc1de00[752] 'usermode-agent' THREAD: ef63e000
GPR00: cc00cc00 ef63fe60 efc1de00 efc1de00 efc1f700 c04c8000 00258560 ffffffff
GPR08: ffda8a00 40000000 00001fda c0500000 49eaebbd 1008b654 3ff8a900 00000000
GPR16: 00000000 eed84c40 c03b4570 c04ee4d0 c04ca870 ef63e03c 00000000 00000000
GPR24: c04f7ee8 c04ee4c0 00000004 c04ca440 ef63e000 efc1f700 c04ca440 efc1de00
NIP [c00081a0] __switch_to+0xac/0x104
LR [c03a9560] schedule+0x20c/0x3f4
Call Trace:
[ef63fe60] [efc1f700] 0xefc1f700 (unreliable)
[ef63fe70] [c03a9560] schedule+0x20c/0x3f4
[ef63fec0] [c00429e0] do_wait+0x1a4/0x278
[ef63fef0] [c0042b44] sys_wait4+0x90/0xf8
[ef63ff40] [c00106d4] ret_from_syscall+0x0/0x4
------------------------------------------
Actually, this problem is caused by enabling On Chip Debugging, when On Chip Debugging is enabled, we enable MSR_DE as below:
#define MSR_KERNEL (MSR_ME|MSR_RI|MSR_CE|MSR_DE)
If I comment out "mtspr(SPRN_DBCR0, thread->dbcr0);" in prime_debug_regs() function,
then it will be ok.
Here is my analysis for this problem:
Run 'usermode-agent' application will set Internal Debug Mode(IDM) and Instruction Complete Debug Event(ICMP)flags for thread.
As MSR_DE is enabled, when execute context switching in prime_debug_regs(), thread->dbcr0 would write to SPRN_DBCR0 register.
So this will enable Instruction Complete Debug Event interrupt, and it will cause a kernel-mode
exception right now, it will be handled in native_DebugException(), then kernel detected
this exception not happens in user-mode, lastly kernel call die() and kill current process.
Quoted 4 lines
So my question is could I just comment out "mtspr(SPRN_DBCR0, thread->dbcr0);" in prime_debug_regs()?
I'm sure whether or not it will impose a bad impact on debugging.
I believe it would have such an impact. I don't see that user-mode debugging would be enabled at all.
Maybe something like this untested patch:
arch/powerpc/kernel/process.c +0 -0
index 84906d3..0e7d1cf 100644
@@ -323,6 +323,13 @@ static void set_debug_reg_defaults(struct thread_struct *thread)
 
  static void prime_debug_regs(struct thread_struct *thread)
  {

arch/powerpc/kernel/process.c static void set_debug_reg_defaults(struct thread_struct *thread) · line 335

Quoted 10 lines

arch/powerpc/kernel/process.c +7 -0

+	/*
+	 * If we're setting up debug events for user space, make sure they
+	 * don't fire in kernel space before we get to user space
+	 */
+	if (thread->dbcr0&  DBCR0_IDM)
+		mtmsr(mfmsr()&  ~MSR_DE);
+
  	mtspr(SPRN_IAC1, thread->iac1);
  	mtspr(SPRN_IAC2, thread->iac2);
  #if CONFIG_PPC_ADV_DEBUG_IACS>  2

Thanks for your reply, Dave, I know where the problem is.

Thanks,
Xufeng Zhang

Benjamin Herrenschmidt

2010-12-09 03:26 UTC #3 lore raw

Quoted 11 lines · xufeng zhang

Quoted 11 lines
I believe it would have such an impact. I don't see that user-mode debugging would be enabled at all.
Maybe something like this untested patch:
arch/powerpc/kernel/process.c +0 -0
index 84906d3..0e7d1cf 100644
@@ -323,6 +323,13 @@ static void set_debug_reg_defaults(struct thread_struct *thread)
 

Quoted 15 lines

Quoted 4 lines
arch/powerpc/kernel/process.c +0 -0
  static void prime_debug_regs(struct thread_struct *thread)
  {
arch/powerpc/kernel/process.c static void set_debug_reg_defaults(struct thread_struct *thread)
Quoted 10 lines
arch/powerpc/kernel/process.c +7 -0
+	/*
+	 * If we're setting up debug events for user space, make sure they
+	 * don't fire in kernel space before we get to user space
+	 */
+	if (thread->dbcr0&  DBCR0_IDM)
+		mtmsr(mfmsr()&  ~MSR_DE);
+
  	mtspr(SPRN_IAC1, thread->iac1);
  	mtspr(SPRN_IAC2, thread->iac2);
  #if CONFIG_PPC_ADV_DEBUG_IACS>  2
Thanks for your reply, Dave, I know where the problem is.

So is there a kernel bug we need to fix ?

Cheers,
Ben.