Commit 43c09ce7 authored May 10, 2007 by Hirokazu Takata Committed by Linus Torvalds May 11, 2007

m32r: fix switch_to macro to push/pop frame pointer if needed



This patch fixes a rarely-happened but severe scheduling problem of
the recent m32r kernel of 2.6.17-rc3 or later.

In the following previous m32r patch, the switch_to macro was
modified not to do unnecessary push/pop operations for tuning.
> [PATCH] m32r: update switch_to macro for tuning
> 4127272c

In this modification, only 'lr' and 'sp' registers are push/pop'ed,
assuming that the m32r kernel is always compiled with
-fomit-frame-pointer option.

However, in 2.6 kernel, kernel/sched.c is irregularly compiled
with -fno-omit-frame-pointer if CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER
is not defined.

 -- kernel/Makefile --
   :
 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
 endif
   :
 ---

Therefore, for the recent m32r kernel, we have to push/pop 'fp'
(frame pointer) if CONFIG_FRAME_POINTER is defined or
CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER is not defined.

Signed-off-by: Hitoshi Yamamoto <hitoshiy@linux-m32r.org>
Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 44316634

arch/m32r/Kconfig

+4 −0

Original line number	Diff line number	Diff line
		@@ -241,6 +241,10 @@ config GENERIC_CALIBRATE_DELAY
		bool
		default y

		config SCHED_NO_NO_OMIT_FRAME_POINTER
		bool
		default y

		config PREEMPT
		bool "Preemptible Kernel"
		help

include/asm-m32r/system.h

+11 −0

Original line number	Diff line number	Diff line
		@@ -21,12 +21,22 @@
		* `next' and `prev' should be struct task_struct, but it isn't always defined
		*/

		#if defined(CONFIG_FRAME_POINTER) \|\| \
		!defined(CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER)
		#define M32R_PUSH_FP " push fp\n"
		#define M32R_POP_FP " pop fp\n"
		#else
		#define M32R_PUSH_FP ""
		#define M32R_POP_FP ""
		#endif

		#define switch_to(prev, next, last) do { \
		__asm__ __volatile__ ( \
		" seth lr, #high(1f) \n" \
		" or3 lr, lr, #low(1f) \n" \
		" st lr, @%4 ; store old LR \n" \
		" ld lr, @%5 ; load new LR \n" \
		M32R_PUSH_FP \
		" st sp, @%2 ; store old SP \n" \
		" ld sp, @%3 ; load new SP \n" \
		" push %1 ; store `prev' on new stack \n" \
		@@ -34,6 +44,7 @@
		" .fillinsn \n" \
		"1: \n" \
		" pop %0 ; restore `__last' from new stack \n" \
		M32R_POP_FP \
		: "=r" (last) \
		: "0" (prev), \
		"r" (&(prev->thread.sp)), "r" (&(next->thread.sp)), \

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