[patch 08/37] uml: fix unreasonably long udelay

[Greg KH]

-stable review patch.  If anyone has any objections, please let us know.

------------------
From: "Paolo 'Blaisorblade' Giarrusso" <blaisorblade@xxxxxxxx>

Currently we have a confused udelay implementation.

* __const_udelay does not accept usecs but xloops in i386 and x86_64
* our implementation requires usecs as arg
* it gets a xloops count when called by asm/arch/delay.h

Bugs related to this (extremely long shutdown times) where reported by some
x86_64 users, especially using Device Mapper.

To hit this bug, a compile-time constant time parameter must be passed - that's
why UML seems to work most times.
Fix this with a simple udelay implementation.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 arch/um/sys-i386/delay.c   |   11 -----------
 arch/um/sys-x86_64/delay.c |   11 -----------
 include/asm-um/delay.h     |   17 ++++++++++++++---
 3 files changed, 14 insertions(+), 25 deletions(-)

--- a/arch/um/sys-i386/delay.c
+++ b/arch/um/sys-i386/delay.c
@@ -27,14 +27,3 @@ void __udelay(unsigned long usecs)
 }
 
 EXPORT_SYMBOL(__udelay);
-
-void __const_udelay(unsigned long usecs)
-{
-	int i, n;
-
-	n = (loops_per_jiffy * HZ * usecs) / MILLION;
-        for(i=0;i<n;i++)
-                cpu_relax();
-}
-
-EXPORT_SYMBOL(__const_udelay);
--- a/arch/um/sys-x86_64/delay.c
+++ b/arch/um/sys-x86_64/delay.c
@@ -28,14 +28,3 @@ void __udelay(unsigned long usecs)
 }
 
 EXPORT_SYMBOL(__udelay);
-
-void __const_udelay(unsigned long usecs)
-{
-	unsigned long i, n;
-
-	n = (loops_per_jiffy * HZ * usecs) / MILLION;
-        for(i=0;i<n;i++)
-                cpu_relax();
-}
-
-EXPORT_SYMBOL(__const_udelay);
--- a/include/asm-um/delay.h
+++ b/include/asm-um/delay.h
@@ -1,9 +1,20 @@
 #ifndef __UM_DELAY_H
 #define __UM_DELAY_H
 
-#include "asm/arch/delay.h"
-#include "asm/archparam.h"
-
 #define MILLION 1000000
 
+/* Undefined on purpose */
+extern void __bad_udelay(void);
+
+extern void __udelay(unsigned long usecs);
+extern void __delay(unsigned long loops);
+
+#define udelay(n) ((__builtin_constant_p(n) && (n) > 20000) ? \
+	__bad_udelay() : __udelay(n))
+
+/* It appears that ndelay is not used at all for UML, and has never been
+ * implemented. */
+extern void __unimplemented_ndelay(void);
+#define ndelay(n) __unimplemented_ndelay()
+
 #endif

-- 
-
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