Re: RFC: remove set_fs for m68k

[Christoph Hellwig <hch@xxxxxx>]

Hi Michael,

from looking at your patches I suspect the 040 traps might be able
to be called witha different fc.  Can you check if the below patch,
which is a cut down version of your changes makes all the issues
go away?

diff --git a/arch/m68k/include/asm/processor.h b/arch/m68k/include/asm/processor.h
index debb4537eab5..a554e529fd26 100644
--- a/arch/m68k/include/asm/processor.h
+++ b/arch/m68k/include/asm/processor.h
@@ -94,6 +94,13 @@ static inline void set_fc(unsigned long val)
 			      "movec %0,%/dfc\n\t"
 			      : /* no outputs */ : "r" (val) : "memory");
 }
+static inline unsigned long get_fc(void)
+{
+	unsigned long val;
+	__asm__ ("movec %/dfc,%0":"=r" (val):);
+	WARN_ON_ONCE(val != USER_DATA);
+	return val;
+}
 #else
 static inline void set_fc(unsigned long val)
 {
diff --git a/arch/m68k/kernel/traps.c b/arch/m68k/kernel/traps.c
index c5e0a4f93bd5..1b073299fa55 100644
--- a/arch/m68k/kernel/traps.c
+++ b/arch/m68k/kernel/traps.c
@@ -181,6 +181,7 @@ static inline void access_error060 (struct frame *fp)
 static inline unsigned long probe040(int iswrite, unsigned long addr, int wbs)
 {
 	unsigned long mmusr;
+	unsigned long old_fc = get_fc();
 
 	set_fc(wbs);
 
@@ -191,7 +192,7 @@ static inline unsigned long probe040(int iswrite, unsigned long addr, int wbs)
 
 	asm volatile (".chip 68040; movec %%mmusr,%0; .chip 68k" : "=r" (mmusr));
 
-	set_fc(USER_DATA);
+	set_fc(old_fc);
 
 	return mmusr;
 }
@@ -200,6 +201,7 @@ static inline int do_040writeback1(unsigned short wbs, unsigned long wba,
 				   unsigned long wbd)
 {
 	int res = 0;
+	unsigned long old_fc = get_fc();
 
 	set_fc(wbs);
 
@@ -215,7 +217,7 @@ static inline int do_040writeback1(unsigned short wbs, unsigned long wba,
 		break;
 	}
 
-	set_fc(USER_DATA);
+	set_fc(old_fc);
 
 	pr_debug("do_040writeback1, res=%d\n", res);