Re: Random crashes with 2.6.27-rc3 on PPC

Started by Andreas Schwab on Aug 24, 2008 · 3 messages from 3 authors · Last reply Aug 24, 2008

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Re: Random crashes with 2.6.27-rc3 on PPC

From: Andreas Schwab <hidden>
Date: 2008-08-24 14:46:50 

Michael Buesch [off-list ref] writes:

The following workaround seems to fix the crashes on powerpc.
However, this patch is clearly not what we want for other architectures,
as they might need -fno-omit-frame-pointer to function properly.
This has a better chance to be accepted. :-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 8b5a7d3..f9a2e48 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -394,7 +394,7 @@ config LOCKDEP
 	bool
 	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
 	select STACKTRACE
-	select FRAME_POINTER if !X86 && !MIPS
+	select FRAME_POINTER if !X86 && !MIPS && !PPC
 	select KALLSYMS
 	select KALLSYMS_ALL
quoted hunk
Index: linux-2.6/kernel/Makefile
===================================================================
--- linux-2.6.orig/kernel/Makefile	2008-08-24 11:50:23.000000000 +0200
+++ linux-2.6/kernel/Makefile	2008-08-24 12:15:54.000000000 +0200
@@ -92,13 +92,13 @@ obj-$(CONFIG_SMP) += sched_cpupri.o
 ifneq ($(CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER),y)
 # According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is
 # needed for x86 only.  Why this used to be enabled for all architectures is beyond
 # me.  I suspect most platforms don't need this, but until we know that for sure
 # I turn this off for IA-64 only.  Andreas Schwab says it's also needed on m68k
 # to get a correct value for the wait-channel (WCHAN in ps). --davidm
-CFLAGS_sched.o := $(PROFILING) -fno-omit-frame-pointer
+CFLAGS_sched.o := $(PROFILING)
CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER is already enabled on powerpc.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: Random crashes with 2.6.27-rc3 on PPC

From: Michael Buesch <hidden>
Date: 2008-08-24 15:01:02 

On Sunday 24 August 2008 16:46:38 Andreas Schwab wrote:
quoted hunk
Michael Buesch [off-list ref] writes:
quoted
The following workaround seems to fix the crashes on powerpc.
However, this patch is clearly not what we want for other architectures,
as they might need -fno-omit-frame-pointer to function properly.
This has a better chance to be accepted. :-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 8b5a7d3..f9a2e48 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -394,7 +394,7 @@ config LOCKDEP
 	bool
 	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
 	select STACKTRACE
-	select FRAME_POINTER if !X86 && !MIPS
+	select FRAME_POINTER if !X86 && !MIPS && !PPC
 	select KALLSYMS
 	select KALLSYMS_ALL
This is not what my patch is doing.
Your patch always forces FRAME_POINTER off. At least as far as lockdep is concerned.
What about other parts of the kernel that enable FRAME_POINTER?

I think this should be fixed in the makefile by substitution of
-fno-omit-frame-pointer on PPC (and probably depending on the compiler
version).

Otherwise, if somebody else decides to do select FRAME_POINTER in some other
code, the bug will reappear.
I'm also not sure if it's desired to always force FRAME_POINTER off.

-- 
Greetings Michael.

Re: Random crashes with 2.6.27-rc3 on PPC

From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: 2008-08-24 22:40:18 

On Sun, 2008-08-24 at 16:46 +0200, Andreas Schwab wrote:
Michael Buesch [off-list ref] writes:
quoted
The following workaround seems to fix the crashes on powerpc.
However, this patch is clearly not what we want for other architectures,
as they might need -fno-omit-frame-pointer to function properly.
This has a better chance to be accepted. :-)
Unfortunately, that won't solve the FTRACE problem.

Ben.
quoted hunk
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 8b5a7d3..f9a2e48 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -394,7 +394,7 @@ config LOCKDEP
 	bool
 	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
 	select STACKTRACE
-	select FRAME_POINTER if !X86 && !MIPS
+	select FRAME_POINTER if !X86 && !MIPS && !PPC
 	select KALLSYMS
 	select KALLSYMS_ALL
quoted
Index: linux-2.6/kernel/Makefile
===================================================================
--- linux-2.6.orig/kernel/Makefile	2008-08-24 11:50:23.000000000 +0200
+++ linux-2.6/kernel/Makefile	2008-08-24 12:15:54.000000000 +0200
@@ -92,13 +92,13 @@ obj-$(CONFIG_SMP) += sched_cpupri.o
 ifneq ($(CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER),y)
 # According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is
 # needed for x86 only.  Why this used to be enabled for all architectures is beyond
 # me.  I suspect most platforms don't need this, but until we know that for sure
 # I turn this off for IA-64 only.  Andreas Schwab says it's also needed on m68k
 # to get a correct value for the wait-channel (WCHAN in ps). --davidm
-CFLAGS_sched.o := $(PROFILING) -fno-omit-frame-pointer
+CFLAGS_sched.o := $(PROFILING)
CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER is already enabled on powerpc.

Andreas.
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