avoid overflows in kernel/time.c

When the conversion factor between jiffies and milli- or microseconds is
not a single multiply or divide, as for the case of HZ == 300, we currently
do a multiply followed by a divide.  The intervening result, however, is
subject to overflows, especially since the fraction is not simplified (for
HZ == 300, we multiply by 300 and divide by 1000).

This is exposed to the user when passing a large timeout to poll(), for
example.

This patch replaces the multiply-divide with a reciprocal multiplication on
32-bit platforms.  When the input is an unsigned long, there is no portable
way to do this on 64-bit platforms there is no portable way to do this
since it requires a 128-bit intermediate result (which gcc does support on
64-bit platforms but may generate libgcc calls, e.g.  on 64-bit s390), but
since the output is a 32-bit integer in the cases affected, just simplify
the multiply-divide (*3/10 instead of *300/1000).

The reciprocal multiply used can have off-by-one errors in the upper half
of the valid output range.  This could be avoided at the expense of having
to deal with a potential 65-bit intermediate result.  Since the intent is
to avoid overflow problems and most of the other time conversions are only
semiexact, the off-by-one errors were considered an acceptable tradeoff.

At Ralf Baechle's suggestion, this version uses a Perl script to compute
the necessary constants.  We already have dependencies on Perl for kernel
compiles.  This does, however, require the Perl module Math::BigInt, which
is included in the standard Perl distribution starting with version 5.8.0.
In order to support older versions of Perl, include a table of canned
constants in the script itself, and structure the script so that
Math::BigInt isn't required if pulling values from said table.

Running the script requires that the HZ value is available from the
Makefile.  Thus, this patch also adds the Kconfig variable CONFIG_HZ to the
architectures which didn't already have it (alpha, cris, frv, h8300, m32r,
m68k, m68knommu, sparc, v850, and xtensa.) It does *not* touch the sh or
sh64 architectures, since Paul Mundt has dealt with those separately in the
sh tree.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Ralf Baechle <ralf@linux-mips.org>,
Cc: Sam Ravnborg <sam@ravnborg.org>,
Cc: Paul Mundt <lethal@linux-sh.org>,
Cc: Richard Henderson <rth@twiddle.net>,
Cc: Michael Starvik <starvik@axis.com>,
Cc: David Howells <dhowells@redhat.com>,
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>,
Cc: Hirokazu Takata <takata@linux-m32r.org>,
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
Cc: Roman Zippel <zippel@linux-m68k.org>,
Cc: William L. Irwin <sparclinux@vger.kernel.org>,
Cc: Chris Zankel <chris@zankel.net>,
Cc: H. Peter Anvin <hpa@zytor.com>,
Cc: Jan Engelhardt <jengelh@computergmbh.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/alpha/Kconfig

@@ -615,6 +615,11 @@ config VERBOSE_MCHECK_ON
 
 	  Take the default (1) unless you want more control or more info.
 
+config HZ
+	int
+	default 1200 if ALPHA_RAWHIDE
+	default 1024
+
 source "drivers/pci/Kconfig"
 source "drivers/eisa/Kconfig"
 

arch/cris/Kconfig

@@ -55,6 +55,10 @@ config CRIS
 	bool
 	default y
 
+config HZ
+	int
+	default 100
+
 source "init/Kconfig"
 
 menu "General setup"

arch/frv/Kconfig

@@ -57,6 +57,10 @@ config ARCH_HAS_ILOG2_U64
 	bool
 	default y
 
+config HZ
+	int
+	default 1000
+
 mainmenu "Fujitsu FR-V Kernel Configuration"
 
 source "init/Kconfig"

arch/h8300/Kconfig

@@ -82,6 +82,10 @@ config PCI
 	bool
 	default n
 
+config HZ
+	int
+	default 100
+
 source "init/Kconfig"
 
 source "arch/h8300/Kconfig.cpu"

arch/m32r/Kconfig

@@ -38,6 +38,10 @@ config NO_DMA
 config ARCH_SUPPORTS_AOUT
 	def_bool y
 
+config HZ
+	int
+	default 100
+
 source "init/Kconfig"
 
 

arch/m68k/Kconfig

@@ -55,6 +55,10 @@ config NO_DMA
 config ARCH_SUPPORTS_AOUT
 	def_bool y
 
+config HZ
+	int
+	default 100
+
 mainmenu "Linux/68k Kernel Configuration"
 
 source "init/Kconfig"

arch/m68knommu/Kconfig

@@ -525,6 +525,11 @@ config 4KSTACKS
 	  running more threads on a system and also reduces the pressure
 	  on the VM subsystem for higher order allocations.
 
+config HZ
+	int
+	default 1000 if CLEOPATRA
+	default 100
+
 comment "RAM configuration"
 
 config RAMBASE

arch/sparc/Kconfig

@@ -30,6 +30,10 @@ config OF
 config ARCH_SUPPORTS_AOUT
 	def_bool y
 
+config HZ
+	int
+	default 100
+
 source "init/Kconfig"
 
 menu "General machine setup"

arch/v850/Kconfig

@@ -215,6 +215,13 @@ menu "Processor type and features"
    	  bool
 	  default !V850E_CACHE && !V850E2_CACHE
 
+   # HZ depends on the platform
+   config HZ
+	  int
+	  default 24  if V850E_SIM || V850E2_SIM85E2
+	  default 122 if V850E2_FPGA85E2C
+	  default 100
+
    #### Misc config
 
    config ROM_KERNEL

arch/xtensa/Kconfig

@@ -49,6 +49,10 @@ config ARCH_HAS_ILOG2_U64
 config NO_IOPORT
 	def_bool y
 
+config HZ
+	int
+	default 100
+
 source "init/Kconfig"
 
 menu "Processor type and features"

include/asm-alpha/param.h

@@ -5,15 +5,7 @@
    hardware ignores reprogramming.  We also need userland buy-in to the 
    change in HZ, since this is visible in the wait4 resources etc.  */
 
-
-#ifndef HZ
-# ifndef CONFIG_ALPHA_RAWHIDE
-#  define HZ	1024
-# else
-#  define HZ	1200
-# endif
-#endif
-
+#define HZ		CONFIG_HZ
 #define USER_HZ		HZ
 
 #define EXEC_PAGESIZE	8192

include/asm-cris/param.h

@@ -3,7 +3,7 @@
 
 /* Currently we assume that HZ=100 is good for CRIS. */
 #ifdef __KERNEL__
-# define HZ		100		/* Internal kernel timer frequency */
+# define HZ		CONFIG_HZ	/* Internal kernel timer frequency */
 # define USER_HZ	100		/* .. some user interfaces are in "ticks" */
 # define CLOCKS_PER_SEC	(USER_HZ)	/* like times() */
 #endif

include/asm-frv/param.h

@@ -2,7 +2,7 @@
 #define _ASM_PARAM_H
 
 #ifdef __KERNEL__
-#define HZ		1000		/* Internal kernel timer frequency */
+#define HZ		CONFIG_HZ	/* Internal kernel timer frequency */
 #define USER_HZ		100		/* .. some user interfaces are in "ticks" */
 #define CLOCKS_PER_SEC	(USER_HZ)	/* like times() */
 #endif

include/asm-h8300/param.h

@@ -3,7 +3,7 @@
 
 
 #ifndef HZ
-#define HZ 100
+#define HZ CONFIG_HZ
 #endif
 
 #ifdef __KERNEL__

include/asm-m32r/param.h

@@ -2,7 +2,7 @@
 #define _ASM_M32R_PARAM_H
 
 #ifdef __KERNEL__
-# define HZ		100		/* Internal kernel timer frequency */
+# define HZ		CONFIG_HZ	/* Internal kernel timer frequency */
 # define USER_HZ	100		/* .. some user interfaces are in "ticks" */
 # define CLOCKS_PER_SEC	(USER_HZ)	/* like times() */
 #endif

include/asm-m68k/param.h

@@ -2,7 +2,7 @@
 #define _M68K_PARAM_H
 
 #ifdef __KERNEL__
-# define HZ		100		/* Internal kernel timer frequency */
+# define HZ		CONFIG_HZ	/* Internal kernel timer frequency */
 # define USER_HZ	100		/* .. some user interfaces are in "ticks" */
 # define CLOCKS_PER_SEC	(USER_HZ)	/* like times() */
 #endif

include/asm-m68knommu/param.h

 #ifndef _M68KNOMMU_PARAM_H
 #define _M68KNOMMU_PARAM_H
 
-
-#if defined(CONFIG_CLEOPATRA)
-#define	HZ 1000
-#endif
-#ifndef HZ
-#define	HZ 100
-#endif
+#define HZ CONFIG_HZ
 
 #ifdef __KERNEL__
 #define	USER_HZ		HZ

include/asm-sparc/param.h

@@ -3,7 +3,7 @@
 #define _ASMSPARC_PARAM_H
 
 #ifdef __KERNEL__
-# define HZ		100	/* Internal kernel timer frequency */
+# define HZ		CONFIG_HZ	/* Internal kernel timer frequency */
 # define USER_HZ	100	/* .. some user interfaces are in "ticks" */
 # define CLOCKS_PER_SEC (USER_HZ)
 #endif

include/asm-v850/anna.h

@@ -134,10 +134,4 @@ extern void anna_uart_pre_configure (unsigned chan,
 #define V850E_TIMER_D_TMCD_CS_MIN	1 /* min 2^1 divider */
 
 
-/* For <asm/param.h> */
-#ifndef HZ
-#define HZ	100
-#endif
-
-
 #endif /* __V850_ANNA_H__ */

include/asm-v850/as85ep1.h

@@ -149,10 +149,4 @@ extern void as85ep1_uart_pre_configure (unsigned chan,
 #define V850E_TIMER_D_TMCD_CS_MIN	2 /* min 2^2 divider */
 
 
-/* For <asm/param.h> */
-#ifndef HZ
-#define HZ	100
-#endif
-
-
 #endif /* __V850_AS85EP1_H__ */