[PATCH 1/3] futex: remove duplicated code

[PATCH 1/3] futex: remove duplicated code

[Jiri Slaby]

There is code duplicated over all architecture's headers for
futex_atomic_op_inuser. Namely op decoding, access_ok check for uaddr,
and comparison of the result.

Remove this duplication and leave up to the arches only the needed
assembly which is now in arch_futex_atomic_op_inuser.

Note that s390 removed access_ok check in d12a29703 ("s390/uaccess:
remove pointless access_ok() checks") as access_ok there returns true.
We introduce it back to the helper for the sake of simplicity (it gets
optimized away anyway).

Signed-off-by: Jiri Slaby <jslaby at suse.cz>
Cc: Richard Henderson <rth at twiddle.net>
Cc: Ivan Kokshaysky <ink at jurassic.park.msu.ru>
Cc: Matt Turner <mattst88 at gmail.com>
Cc: Vineet Gupta <vgupta at synopsys.com>
Cc: Russell King <linux at armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will.deacon at arm.com>
Cc: Richard Kuo <rkuo at codeaurora.org>
Cc: Tony Luck <tony.luck at intel.com>
Cc: Fenghua Yu <fenghua.yu at intel.com>
Cc: Michal Simek <monstr at monstr.eu>
Cc: Ralf Baechle <ralf at linux-mips.org>
Cc: Jonas Bonn <jonas at southpole.se>
Cc: Stefan Kristiansson <stefan.kristiansson at saunalahti.fi>
Cc: Stafford Horne <shorne at gmail.com>
Cc: "James E.J. Bottomley" <jejb at parisc-linux.org>
Cc: Helge Deller <deller at gmx.de>
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Paul Mackerras <paulus at samba.org>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Martin Schwidefsky <schwidefsky at de.ibm.com>
Cc: Heiko Carstens <heiko.carstens at de.ibm.com>
Cc: Yoshinori Sato <ysato at users.sourceforge.jp>
Cc: Rich Felker <dalias at libc.org>
Cc: "David S. Miller" <davem at davemloft.net>
Cc: Chris Metcalf <cmetcalf at mellanox.com>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Ingo Molnar <mingo at redhat.com>
Cc: "H. Peter Anvin" <hpa at zytor.com>
Cc: Chris Zankel <chris at zankel.net>
Cc: Max Filippov <jcmvbkbc at gmail.com>
Cc: Arnd Bergmann <arnd at arndb.de>
Cc: <x86 at kernel.org>
Cc: <linux-alpha at vger.kernel.org>
Cc: <linux-kernel at vger.kernel.org>
Cc: <linux-snps-arc at lists.infradead.org>
Cc: <linux-arm-kernel at lists.infradead.org>
Cc: <linux-hexagon at vger.kernel.org>
Cc: <linux-ia64 at vger.kernel.org>
Cc: <linux-mips at linux-mips.org>
Cc: <openrisc at lists.librecores.org>
Cc: <linux-parisc at vger.kernel.org>
Cc: <linuxppc-dev at lists.ozlabs.org>
Cc: <linux-s390 at vger.kernel.org>
Cc: <linux-sh at vger.kernel.org>
Cc: <sparclinux at vger.kernel.org>
Cc: <linux-xtensa at linux-xtensa.org>
Cc: <linux-arch at vger.kernel.org>
---
 arch/alpha/include/asm/futex.h      | 26 ++++---------------
 arch/arc/include/asm/futex.h        | 40 ++++-------------------------
 arch/arm/include/asm/futex.h        | 26 +++----------------
 arch/arm64/include/asm/futex.h      | 26 +++----------------
 arch/frv/include/asm/futex.h        |  3 ++-
 arch/frv/kernel/futex.c             | 27 +++-----------------
 arch/hexagon/include/asm/futex.h    | 38 +++-------------------------
 arch/ia64/include/asm/futex.h       | 25 +++----------------
 arch/microblaze/include/asm/futex.h | 38 +++-------------------------
 arch/mips/include/asm/futex.h       | 25 +++----------------
 arch/openrisc/include/asm/futex.h   | 39 +++--------------------------
 arch/parisc/include/asm/futex.h     | 26 +++----------------
 arch/powerpc/include/asm/futex.h    | 26 ++++---------------
 arch/s390/include/asm/futex.h       | 23 ++++-------------
 arch/sh/include/asm/futex.h         | 26 +++----------------
 arch/sparc/include/asm/futex_64.h   | 26 ++++---------------
 arch/tile/include/asm/futex.h       | 40 ++++-------------------------
 arch/x86/include/asm/futex.h        | 40 ++++-------------------------
 arch/xtensa/include/asm/futex.h     | 27 ++++----------------
 include/asm-generic/futex.h         | 50 +++++++------------------------------
 kernel/futex.c                      | 36 ++++++++++++++++++++++++++
 21 files changed, 127 insertions(+), 506 deletions(-)

diff --git a/arch/alpha/include/asm/futex.h b/arch/alpha/include/asm/futex.h
index f939794363ac..56474690e685 100644
--- a/arch/alpha/include/asm/futex.h
+++ b/arch/alpha/include/asm/futex.h
@@ -29,18 +29,10 @@
 	:	"r" (uaddr), "r"(oparg)				\
 	:	"memory")
 
-static inline int futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
+static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
+		u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, ret;
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
-		return -EFAULT;
 
 	pagefault_disable();
 
@@ -66,17 +58,9 @@ static inline int futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
 
 	pagefault_enable();
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
-		case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
-		case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
-		case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
-		case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
-		case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
-		default: ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
+
 	return ret;
 }
 
diff --git a/arch/arc/include/asm/futex.h b/arch/arc/include/asm/futex.h
index 11e1b1f3acda..eb887dd13e74 100644
--- a/arch/arc/include/asm/futex.h
+++ b/arch/arc/include/asm/futex.h
@@ -73,20 +73,11 @@
 
 #endif
 
-static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
+static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
+		u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, ret;
 
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
-		return -EFAULT;
-
 #ifndef CONFIG_ARC_HAS_LLSC
 	preempt_disable();	/* to guarantee atomic r-m-w of futex op */
 #endif
@@ -118,30 +109,9 @@ static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
 	preempt_enable();
 #endif
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ:
-			ret = (oldval == cmparg);
-			break;
-		case FUTEX_OP_CMP_NE:
-			ret = (oldval != cmparg);
-			break;
-		case FUTEX_OP_CMP_LT:
-			ret = (oldval < cmparg);
-			break;
-		case FUTEX_OP_CMP_GE:
-			ret = (oldval >= cmparg);
-			break;
-		case FUTEX_OP_CMP_LE:
-			ret = (oldval <= cmparg);
-			break;
-		case FUTEX_OP_CMP_GT:
-			ret = (oldval > cmparg);
-			break;
-		default:
-			ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
+
 	return ret;
 }
 
diff --git a/arch/arm/include/asm/futex.h b/arch/arm/include/asm/futex.h
index 6795368ad023..cc414382dab4 100644
--- a/arch/arm/include/asm/futex.h
+++ b/arch/arm/include/asm/futex.h
@@ -128,20 +128,10 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 #endif /* !SMP */
 
 static inline int
-futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
+arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, ret, tmp;
 
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
-		return -EFAULT;
-
 #ifndef CONFIG_SMP
 	preempt_disable();
 #endif
@@ -172,17 +162,9 @@ futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
 	preempt_enable();
 #endif
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
-		case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
-		case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
-		case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
-		case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
-		case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
-		default: ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
+
 	return ret;
 }
 
diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h
index 85c4a8981d47..5bb2fd4674e7 100644
--- a/arch/arm64/include/asm/futex.h
+++ b/arch/arm64/include/asm/futex.h
@@ -48,20 +48,10 @@ do {									\
 } while (0)
 
 static inline int
-futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
+arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, ret, tmp;
 
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
-		return -EFAULT;
-
 	pagefault_disable();
 
 	switch (op) {
@@ -91,17 +81,9 @@ futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
 
 	pagefault_enable();
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
-		case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
-		case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
-		case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
-		case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
-		case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
-		default: ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
+
 	return ret;
 }
 
diff --git a/arch/frv/include/asm/futex.h b/arch/frv/include/asm/futex.h
index 2e1da71e27a4..ab346f5f8820 100644
--- a/arch/frv/include/asm/futex.h
+++ b/arch/frv/include/asm/futex.h
@@ -7,7 +7,8 @@
 #include <asm/errno.h>
 #include <linux/uaccess.h>
 
-extern int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr);
+extern int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
+		u32 __user *uaddr);
 
 static inline int
 futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
diff --git a/arch/frv/kernel/futex.c b/arch/frv/kernel/futex.c
index d155ca9e5098..37f7b2bf7f73 100644
--- a/arch/frv/kernel/futex.c
+++ b/arch/frv/kernel/futex.c
@@ -186,20 +186,10 @@ static inline int atomic_futex_op_xchg_xor(int oparg, u32 __user *uaddr, int *_o
 /*
  * do the futex operations
  */
-int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
+int arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, ret;
 
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
-		return -EFAULT;
-
 	pagefault_disable();
 
 	switch (op) {
@@ -225,18 +215,9 @@ int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
 
 	pagefault_enable();
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
-		case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
-		case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
-		case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
-		case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
-		case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
-		default: ret = -ENOSYS; break;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
 
 	return ret;
 
-} /* end futex_atomic_op_inuser() */
+} /* end arch_futex_atomic_op_inuser() */
diff --git a/arch/hexagon/include/asm/futex.h b/arch/hexagon/include/asm/futex.h
index 7e597f8434da..c607b77c8215 100644
--- a/arch/hexagon/include/asm/futex.h
+++ b/arch/hexagon/include/asm/futex.h
@@ -31,18 +31,9 @@
 
 
 static inline int
-futex_atomic_op_inuser(int encoded_op, int __user *uaddr)
+arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, ret;
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
-		return -EFAULT;
 
 	pagefault_disable();
 
@@ -72,30 +63,9 @@ futex_atomic_op_inuser(int encoded_op, int __user *uaddr)
 
 	pagefault_enable();
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ:
-			ret = (oldval == cmparg);
-			break;
-		case FUTEX_OP_CMP_NE:
-			ret = (oldval != cmparg);
-			break;
-		case FUTEX_OP_CMP_LT:
-			ret = (oldval < cmparg);
-			break;
-		case FUTEX_OP_CMP_GE:
-			ret = (oldval >= cmparg);
-			break;
-		case FUTEX_OP_CMP_LE:
-			ret = (oldval <= cmparg);
-			break;
-		case FUTEX_OP_CMP_GT:
-			ret = (oldval > cmparg);
-			break;
-		default:
-			ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
+
 	return ret;
 }
 
diff --git a/arch/ia64/include/asm/futex.h b/arch/ia64/include/asm/futex.h
index 76acbcd5c060..6d67dc1eaf2b 100644
--- a/arch/ia64/include/asm/futex.h
+++ b/arch/ia64/include/asm/futex.h
@@ -45,18 +45,9 @@ do {									\
 } while (0)
 
 static inline int
-futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
+arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, ret;
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (! access_ok (VERIFY_WRITE, uaddr, sizeof(u32)))
-		return -EFAULT;
 
 	pagefault_disable();
 
@@ -84,17 +75,9 @@ futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
 
 	pagefault_enable();
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
-		case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
-		case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
-		case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
-		case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
-		case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
-		default: ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
+
 	return ret;
 }
 
diff --git a/arch/microblaze/include/asm/futex.h b/arch/microblaze/include/asm/futex.h
index 01848f056f43..a9dad9e5e132 100644
--- a/arch/microblaze/include/asm/futex.h
+++ b/arch/microblaze/include/asm/futex.h
@@ -29,18 +29,9 @@
 })
 
 static inline int
-futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
+arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, ret;
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
-		return -EFAULT;
 
 	pagefault_disable();
 
@@ -66,30 +57,9 @@ futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
 
 	pagefault_enable();
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ:
-			ret = (oldval == cmparg);
-			break;
-		case FUTEX_OP_CMP_NE:
-			ret = (oldval != cmparg);
-			break;
-		case FUTEX_OP_CMP_LT:
-			ret = (oldval < cmparg);
-			break;
-		case FUTEX_OP_CMP_GE:
-			ret = (oldval >= cmparg);
-			break;
-		case FUTEX_OP_CMP_LE:
-			ret = (oldval <= cmparg);
-			break;
-		case FUTEX_OP_CMP_GT:
-			ret = (oldval > cmparg);
-			break;
-		default:
-			ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
+
 	return ret;
 }
 
diff --git a/arch/mips/include/asm/futex.h b/arch/mips/include/asm/futex.h
index 1de190bdfb9c..a9e61ea54ca9 100644
--- a/arch/mips/include/asm/futex.h
+++ b/arch/mips/include/asm/futex.h
@@ -83,18 +83,9 @@
 }
 
 static inline int
-futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
+arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, ret;
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (! access_ok (VERIFY_WRITE, uaddr, sizeof(u32)))
-		return -EFAULT;
 
 	pagefault_disable();
 
@@ -125,17 +116,9 @@ futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
 
 	pagefault_enable();
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
-		case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
-		case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
-		case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
-		case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
-		case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
-		default: ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
+
 	return ret;
 }
 
diff --git a/arch/openrisc/include/asm/futex.h b/arch/openrisc/include/asm/futex.h
index 778087341977..8fed278a24b8 100644
--- a/arch/openrisc/include/asm/futex.h
+++ b/arch/openrisc/include/asm/futex.h
@@ -30,20 +30,10 @@
 })
 
 static inline int
-futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
+arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, ret;
 
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
-		return -EFAULT;
-
 	pagefault_disable();
 
 	switch (op) {
@@ -68,30 +58,9 @@ futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
 
 	pagefault_enable();
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ:
-			ret = (oldval == cmparg);
-			break;
-		case FUTEX_OP_CMP_NE:
-			ret = (oldval != cmparg);
-			break;
-		case FUTEX_OP_CMP_LT:
-			ret = (oldval < cmparg);
-			break;
-		case FUTEX_OP_CMP_GE:
-			ret = (oldval >= cmparg);
-			break;
-		case FUTEX_OP_CMP_LE:
-			ret = (oldval <= cmparg);
-			break;
-		case FUTEX_OP_CMP_GT:
-			ret = (oldval > cmparg);
-			break;
-		default:
-			ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
+
 	return ret;
 }
 
diff --git a/arch/parisc/include/asm/futex.h b/arch/parisc/include/asm/futex.h
index ac8bd586ace8..06a1a883c72f 100644
--- a/arch/parisc/include/asm/futex.h
+++ b/arch/parisc/include/asm/futex.h
@@ -32,22 +32,12 @@ _futex_spin_unlock_irqrestore(u32 __user *uaddr, unsigned long int *flags)
 }
 
 static inline int
-futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
+arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
 {
 	unsigned long int flags;
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval, ret;
 	u32 tmp;
 
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(*uaddr)))
-		return -EFAULT;
-
 	_futex_spin_lock_irqsave(uaddr, &flags);
 	pagefault_disable();
 
@@ -85,17 +75,9 @@ futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
 	pagefault_enable();
 	_futex_spin_unlock_irqrestore(uaddr, &flags);
 
-	if (ret == 0) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
-		case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
-		case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
-		case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
-		case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
-		case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
-		default: ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
+
 	return ret;
 }
 
diff --git a/arch/powerpc/include/asm/futex.h b/arch/powerpc/include/asm/futex.h
index eaada6c92344..719ed9b61ea7 100644
--- a/arch/powerpc/include/asm/futex.h
+++ b/arch/powerpc/include/asm/futex.h
@@ -29,18 +29,10 @@
 	: "b" (uaddr), "i" (-EFAULT), "r" (oparg) \
 	: "cr0", "memory")
 
-static inline int futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
+static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
+		u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, ret;
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (! access_ok (VERIFY_WRITE, uaddr, sizeof(u32)))
-		return -EFAULT;
 
 	pagefault_disable();
 
@@ -66,17 +58,9 @@ static inline int futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
 
 	pagefault_enable();
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
-		case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
-		case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
-		case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
-		case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
-		case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
-		default: ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
+
 	return ret;
 }
 
diff --git a/arch/s390/include/asm/futex.h b/arch/s390/include/asm/futex.h
index a4811aa0304d..8f8eec9e1198 100644
--- a/arch/s390/include/asm/futex.h
+++ b/arch/s390/include/asm/futex.h
@@ -21,17 +21,12 @@
 		: "0" (-EFAULT), "d" (oparg), "a" (uaddr),		\
 		  "m" (*uaddr) : "cc");
 
-static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
+static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
+		u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, newval, ret;
 
 	load_kernel_asce();
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
 
 	pagefault_disable();
 	switch (op) {
@@ -60,17 +55,9 @@ static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
 	}
 	pagefault_enable();
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
-		case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
-		case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
-		case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
-		case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
-		case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
-		default: ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
+
 	return ret;
 }
 
diff --git a/arch/sh/include/asm/futex.h b/arch/sh/include/asm/futex.h
index d0078747d308..8f8cf941a8cd 100644
--- a/arch/sh/include/asm/futex.h
+++ b/arch/sh/include/asm/futex.h
@@ -27,21 +27,12 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 	return atomic_futex_op_cmpxchg_inatomic(uval, uaddr, oldval, newval);
 }
 
-static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
+static inline int arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval,
+		u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	u32 oparg = (encoded_op << 8) >> 20;
-	u32 cmparg = (encoded_op << 20) >> 20;
 	u32 oldval, newval, prev;
 	int ret;
 
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
-		return -EFAULT;
-
 	pagefault_disable();
 
 	do {
@@ -80,17 +71,8 @@ static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
 
 	pagefault_enable();
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
-		case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
-		case FUTEX_OP_CMP_LT: ret = ((int)oldval < (int)cmparg); break;
-		case FUTEX_OP_CMP_GE: ret = ((int)oldval >= (int)cmparg); break;
-		case FUTEX_OP_CMP_LE: ret = ((int)oldval <= (int)cmparg); break;
-		case FUTEX_OP_CMP_GT: ret = ((int)oldval > (int)cmparg); break;
-		default: ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
 
 	return ret;
 }
diff --git a/arch/sparc/include/asm/futex_64.h b/arch/sparc/include/asm/futex_64.h
index 4e899b0dabf7..1cfd89d92208 100644
--- a/arch/sparc/include/asm/futex_64.h
+++ b/arch/sparc/include/asm/futex_64.h
@@ -29,22 +29,14 @@
 	: "r" (uaddr), "r" (oparg), "i" (-EFAULT)	\
 	: "memory")
 
-static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
+static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
+		u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, ret, tem;
 
-	if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
-		return -EFAULT;
 	if (unlikely((((unsigned long) uaddr) & 0x3UL)))
 		return -EINVAL;
 
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
 	pagefault_disable();
 
 	switch (op) {
@@ -69,17 +61,9 @@ static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
 
 	pagefault_enable();
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
-		case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
-		case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
-		case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
-		case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
-		case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
-		default: ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
+
 	return ret;
 }
 
diff --git a/arch/tile/include/asm/futex.h b/arch/tile/include/asm/futex.h
index e64a1b75fc38..83c1e639b411 100644
--- a/arch/tile/include/asm/futex.h
+++ b/arch/tile/include/asm/futex.h
@@ -106,12 +106,9 @@
 	lock = __atomic_hashed_lock((int __force *)uaddr)
 #endif
 
-static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
+static inline int arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval,
+		u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int uninitialized_var(val), ret;
 
 	__futex_prolog();
@@ -119,12 +116,6 @@ static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
 	/* The 32-bit futex code makes this assumption, so validate it here. */
 	BUILD_BUG_ON(sizeof(atomic_t) != sizeof(int));
 
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
-		return -EFAULT;
-
 	pagefault_disable();
 	switch (op) {
 	case FUTEX_OP_SET:
@@ -148,30 +139,9 @@ static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
 	}
 	pagefault_enable();
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ:
-			ret = (val == cmparg);
-			break;
-		case FUTEX_OP_CMP_NE:
-			ret = (val != cmparg);
-			break;
-		case FUTEX_OP_CMP_LT:
-			ret = (val < cmparg);
-			break;
-		case FUTEX_OP_CMP_GE:
-			ret = (val >= cmparg);
-			break;
-		case FUTEX_OP_CMP_LE:
-			ret = (val <= cmparg);
-			break;
-		case FUTEX_OP_CMP_GT:
-			ret = (val > cmparg);
-			break;
-		default:
-			ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = val;
+
 	return ret;
 }
 
diff --git a/arch/x86/include/asm/futex.h b/arch/x86/include/asm/futex.h
index b4c1f5453436..f4dc9b63bdda 100644
--- a/arch/x86/include/asm/futex.h
+++ b/arch/x86/include/asm/futex.h
@@ -41,20 +41,11 @@
 		       "+m" (*uaddr), "=&r" (tem)		\
 		     : "r" (oparg), "i" (-EFAULT), "1" (0))
 
-static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
+static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
+		u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, ret, tem;
 
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
-		return -EFAULT;
-
 	pagefault_disable();
 
 	switch (op) {
@@ -80,30 +71,9 @@ static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
 
 	pagefault_enable();
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ:
-			ret = (oldval == cmparg);
-			break;
-		case FUTEX_OP_CMP_NE:
-			ret = (oldval != cmparg);
-			break;
-		case FUTEX_OP_CMP_LT:
-			ret = (oldval < cmparg);
-			break;
-		case FUTEX_OP_CMP_GE:
-			ret = (oldval >= cmparg);
-			break;
-		case FUTEX_OP_CMP_LE:
-			ret = (oldval <= cmparg);
-			break;
-		case FUTEX_OP_CMP_GT:
-			ret = (oldval > cmparg);
-			break;
-		default:
-			ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
+
 	return ret;
 }
 
diff --git a/arch/xtensa/include/asm/futex.h b/arch/xtensa/include/asm/futex.h
index b39531babec0..eaaf1ebcc7a4 100644
--- a/arch/xtensa/include/asm/futex.h
+++ b/arch/xtensa/include/asm/futex.h
@@ -44,18 +44,10 @@
 	: "r" (uaddr), "I" (-EFAULT), "r" (oparg)	\
 	: "memory")
 
-static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
+static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
+		u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, ret;
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
-		return -EFAULT;
 
 #if !XCHAL_HAVE_S32C1I
 	return -ENOSYS;
@@ -89,19 +81,10 @@ static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
 
 	pagefault_enable();
 
-	if (ret)
-		return ret;
+	if (!ret)
+		*oval = oldval;
 
-	switch (cmp) {
-	case FUTEX_OP_CMP_EQ: return (oldval == cmparg);
-	case FUTEX_OP_CMP_NE: return (oldval != cmparg);
-	case FUTEX_OP_CMP_LT: return (oldval < cmparg);
-	case FUTEX_OP_CMP_GE: return (oldval >= cmparg);
-	case FUTEX_OP_CMP_LE: return (oldval <= cmparg);
-	case FUTEX_OP_CMP_GT: return (oldval > cmparg);
-	}
-
-	return -ENOSYS;
+	return ret;
 }
 
 static inline int
diff --git a/include/asm-generic/futex.h b/include/asm-generic/futex.h
index bf2d34c9d804..f0d8b1c51343 100644
--- a/include/asm-generic/futex.h
+++ b/include/asm-generic/futex.h
@@ -13,7 +13,7 @@
  */
 
 /**
- * futex_atomic_op_inuser() - Atomic arithmetic operation with constant
+ * arch_futex_atomic_op_inuser() - Atomic arithmetic operation with constant
  *			  argument and comparison of the previous
  *			  futex value with another constant.
  *
@@ -25,18 +25,11 @@
  * <0 - On error
  */
 static inline int
-futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
+arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval, ret;
 	u32 tmp;
 
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
 	preempt_disable();
 	pagefault_disable();
 
@@ -74,17 +67,9 @@ futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
 	pagefault_enable();
 	preempt_enable();
 
-	if (ret == 0) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
-		case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
-		case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
-		case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
-		case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
-		case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
-		default: ret = -ENOSYS;
-		}
-	}
+	if (ret == 0)
+		*oval = oldval;
+
 	return ret;
 }
 
@@ -126,18 +111,9 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 
 #else
 static inline int
-futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
+arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)
 {
-	int op = (encoded_op >> 28) & 7;
-	int cmp = (encoded_op >> 24) & 15;
-	int oparg = (encoded_op << 8) >> 20;
-	int cmparg = (encoded_op << 20) >> 20;
 	int oldval = 0, ret;
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
-		oparg = 1 << oparg;
-
-	if (! access_ok (VERIFY_WRITE, uaddr, sizeof(u32)))
-		return -EFAULT;
 
 	pagefault_disable();
 
@@ -153,17 +129,9 @@ futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
 
 	pagefault_enable();
 
-	if (!ret) {
-		switch (cmp) {
-		case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
-		case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
-		case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
-		case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
-		case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
-		case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
-		default: ret = -ENOSYS;
-		}
-	}
+	if (!ret)
+		*oval = oldval;
+
 	return ret;
 }
 
diff --git a/kernel/futex.c b/kernel/futex.c
index b687cb22301c..c5ff9850952f 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1457,6 +1457,42 @@ futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
 	return ret;
 }
 
+static int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
+{
+	int op = (encoded_op >> 28) & 7;
+	int cmp = (encoded_op >> 24) & 15;
+	int oparg = (encoded_op << 8) >> 20;
+	int cmparg = (encoded_op << 20) >> 20;
+	int oldval, ret;
+
+	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
+		oparg = 1 << oparg;
+
+	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
+		return -EFAULT;
+
+	ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
+	if (ret)
+		return ret;
+
+	switch (cmp) {
+	case FUTEX_OP_CMP_EQ:
+		return oldval == cmparg;
+	case FUTEX_OP_CMP_NE:
+		return oldval != cmparg;
+	case FUTEX_OP_CMP_LT:
+		return oldval < cmparg;
+	case FUTEX_OP_CMP_GE:
+		return oldval >= cmparg;
+	case FUTEX_OP_CMP_LE:
+		return oldval <= cmparg;
+	case FUTEX_OP_CMP_GT:
+		return oldval > cmparg;
+	default:
+		return -ENOSYS;
+	}
+}
+
 /*
  * Wake up all waiters hashed on the physical page that is mapped
  * to this virtual address:
-- 
2.12.0

[PATCH 1/3] futex: remove duplicated code

[Heiko Carstens]

On Fri, Mar 03, 2017@01:27:10PM +0100, Jiri Slaby wrote:
> There is code duplicated over all architecture's headers for
> futex_atomic_op_inuser. Namely op decoding, access_ok check for uaddr,
> and comparison of the result.
> 
> Remove this duplication and leave up to the arches only the needed
> assembly which is now in arch_futex_atomic_op_inuser.
> 
> Note that s390 removed access_ok check in d12a29703 ("s390/uaccess:
> remove pointless access_ok() checks") as access_ok there returns true.
> We introduce it back to the helper for the sake of simplicity (it gets
> optimized away anyway).
> 
> Signed-off-by: Jiri Slaby <jslaby at suse.cz>
> ---
>  arch/s390/include/asm/futex.h       | 23 ++++-------------
>  include/asm-generic/futex.h         | 50 +++++++------------------------------
>  kernel/futex.c                      | 36 ++++++++++++++++++++++++++

Looks good to me and still boots on s390. Therefore for the s390 bits:
Acked-by: Heiko Carstens <heiko.carstens at de.ibm.com>

Thanks!

[PATCH 1/3] futex: remove duplicated code

[Chris Metcalf]

On 3/3/2017 7:27 AM, Jiri Slaby wrote:
> There is code duplicated over all architecture's headers for
> futex_atomic_op_inuser. Namely op decoding, access_ok check for uaddr,
> and comparison of the result.
>
> Remove this duplication and leave up to the arches only the needed
> assembly which is now in arch_futex_atomic_op_inuser.
>
> Note that s390 removed access_ok check in d12a29703 ("s390/uaccess:
> remove pointless access_ok() checks") as access_ok there returns true.
> We introduce it back to the helper for the sake of simplicity (it gets
> optimized away anyway).
>
> Signed-off-by: Jiri Slaby<jslaby at suse.cz>

Acked-by: Chris Metcalf <cmetcalf at mellanox.com> [for tile]

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com

[PATCH 1/3] futex: remove duplicated code

[Michael Ellerman]

Jiri Slaby <jslaby at suse.cz> writes:

> There is code duplicated over all architecture's headers for
> futex_atomic_op_inuser. Namely op decoding, access_ok check for uaddr,
> and comparison of the result.
>
> Remove this duplication and leave up to the arches only the needed
> assembly which is now in arch_futex_atomic_op_inuser.

Looks OK and boots on powerpc. But I don't think anything's actually
calling those futex ops. Is there a test suite I should run?

Acked-by: Michael Ellerman <mpe at ellerman.id.au> (powerpc)

cheers

[PATCH 1/3] futex: remove duplicated code

[Russell King - ARM Linux]

On Fri, Mar 03, 2017@01:27:10PM +0100, Jiri Slaby wrote:
> diff --git a/arch/arm/include/asm/futex.h b/arch/arm/include/asm/futex.h
> index 6795368ad023..cc414382dab4 100644
> --- a/arch/arm/include/asm/futex.h
> +++ b/arch/arm/include/asm/futex.h
> @@ -128,20 +128,10 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
>  #endif /* !SMP */
>  
>  static inline int
> -futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
> +arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
>  {
> -	int op = (encoded_op >> 28) & 7;
> -	int cmp = (encoded_op >> 24) & 15;
> -	int oparg = (encoded_op << 8) >> 20;
> -	int cmparg = (encoded_op << 20) >> 20;
>  	int oldval = 0, ret, tmp;
>  
> -	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
> -		oparg = 1 << oparg;
> -
> -	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
> -		return -EFAULT;
> -
>  #ifndef CONFIG_SMP
>  	preempt_disable();
>  #endif
> @@ -172,17 +162,9 @@ futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
>  	preempt_enable();
>  #endif
>  
> -	if (!ret) {
> -		switch (cmp) {
> -		case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
> -		case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
> -		case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
> -		case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
> -		case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
> -		case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
> -		default: ret = -ENOSYS;
> -		}
> -	}
> +	if (!ret)
> +		*oval = oldval;
> +
>  	return ret;
>  }
>  
> diff --git a/kernel/futex.c b/kernel/futex.c
> index b687cb22301c..c5ff9850952f 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -1457,6 +1457,42 @@ futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
>  	return ret;
>  }
>  
> +static int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
> +{
> +	int op = (encoded_op >> 28) & 7;
> +	int cmp = (encoded_op >> 24) & 15;
> +	int oparg = (encoded_op << 8) >> 20;
> +	int cmparg = (encoded_op << 20) >> 20;

Hmm.  oparg and cmparg look like they're doing these shifts to get sign
extension of the 12-bit values by assuming that "int" is 32-bit -
probably worth a comment, or for safety, they should be "s32" so it's
not dependent on the bit-width of "int".

> +	int oldval, ret;
> +
> +	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
> +		oparg = 1 << oparg;

I guess it doesn't matter that oparg can be >= the bit size of oparg
(so large values produce an undefined result) as it's no different
from userspace trying to do the same with large shifts.

> +
> +	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
> +		return -EFAULT;
> +
> +	ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
> +	if (ret)
> +		return ret;
> +
> +	switch (cmp) {
> +	case FUTEX_OP_CMP_EQ:
> +		return oldval == cmparg;
> +	case FUTEX_OP_CMP_NE:
> +		return oldval != cmparg;
> +	case FUTEX_OP_CMP_LT:
> +		return oldval < cmparg;
> +	case FUTEX_OP_CMP_GE:
> +		return oldval >= cmparg;
> +	case FUTEX_OP_CMP_LE:
> +		return oldval <= cmparg;
> +	case FUTEX_OP_CMP_GT:
> +		return oldval > cmparg;
> +	default:
> +		return -ENOSYS;
> +	}
> +}
> +
>  /*
>   * Wake up all waiters hashed on the physical page that is mapped
>   * to this virtual address:

As it's no worse than our existing code, for the above,

Acked-by: Russell King <rmk+kernel at armlinux.org.uk>

Thanks.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.

[PATCH 1/3] futex: remove duplicated code

[H. Peter Anvin]

On 03/04/17 05:05, Russell King - ARM Linux wrote:
>>  
>> +static int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
>> +{
>> +	int op = (encoded_op >> 28) & 7;
>> +	int cmp = (encoded_op >> 24) & 15;
>> +	int oparg = (encoded_op << 8) >> 20;
>> +	int cmparg = (encoded_op << 20) >> 20;
> 
> Hmm.  oparg and cmparg look like they're doing these shifts to get sign
> extension of the 12-bit values by assuming that "int" is 32-bit -
> probably worth a comment, or for safety, they should be "s32" so it's
> not dependent on the bit-width of "int".
> 

For readability, perhaps we should make sign- and zero-extension an
explicit facility?

/*
 * Truncate an integer x to n bits, using sign- or
 * zero-extension, respectively.
 */
static inline __const_func__ s32 sex32(s32 x, int n)
{
  return (x << (32-n)) >> (32-n);
}

static inline __const_func__ s64 sex64(s64 x, int n)
{
  return (x << (64-n)) >> (64-n);
}

#define sex(x,y)						\
	((__typeof__(x))					\
	 (((__builtin_constant_p(y) && ((y) <= 32)) ||		\
	   (sizeof(x) <= sizeof(s32)))				\
	  ? sex32((x),(y)) : sex64((x),(y))))

static inline __const_func__ u32 zex32(u32 x, int n)
{
  return (x << (32-n)) >> (32-n);
}

static inline __const_func__ u64 zex64(u64 x, int n)
{
  return (x << (64-n)) >> (64-n);
}

#define zex(x,y)						\
	((__typeof__(x))					\
	 (((__builtin_constant_p(y) && ((y) <= 32)) ||		\
	   (sizeof(x) <= sizeof(u32)))				\
	  ? zex32((x),(y)) : zex64((x),(y))))

[PATCH 1/3] futex: remove duplicated code

[Stafford Horne]

On Sat, Mar 04, 2017@11:15:17AM -0800, H. Peter Anvin wrote:
> On 03/04/17 05:05, Russell King - ARM Linux wrote:
> >>  
> >> +static int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
> >> +{
> >> +	int op = (encoded_op >> 28) & 7;
> >> +	int cmp = (encoded_op >> 24) & 15;
> >> +	int oparg = (encoded_op << 8) >> 20;
> >> +	int cmparg = (encoded_op << 20) >> 20;
> > 
> > Hmm.  oparg and cmparg look like they're doing these shifts to get sign
> > extension of the 12-bit values by assuming that "int" is 32-bit -
> > probably worth a comment, or for safety, they should be "s32" so it's
> > not dependent on the bit-width of "int".
> > 
> 
> For readability, perhaps we should make sign- and zero-extension an
> explicit facility?

There is some of this in already here, 32 and 64 bit versions:

  include/linux/bitops.h

Do we really need zero extension? It seems the same.

Example implementation from bitops.h

static inline __s32 sign_extend32(__u32 value, int index)
{
        __u8 shift = 31 - index;
        return (__s32)(value << shift) >> shift;
}

> /*
>  * Truncate an integer x to n bits, using sign- or
>  * zero-extension, respectively.
>  */
> static inline __const_func__ s32 sex32(s32 x, int n)
> {
>   return (x << (32-n)) >> (32-n);
> }
> 
> static inline __const_func__ s64 sex64(s64 x, int n)
> {
>   return (x << (64-n)) >> (64-n);
> }
> 
> #define sex(x,y)						\
> 	((__typeof__(x))					\
> 	 (((__builtin_constant_p(y) && ((y) <= 32)) ||		\
> 	   (sizeof(x) <= sizeof(s32)))				\
> 	  ? sex32((x),(y)) : sex64((x),(y))))
> 
> static inline __const_func__ u32 zex32(u32 x, int n)
> {
>   return (x << (32-n)) >> (32-n);
> }
> 
> static inline __const_func__ u64 zex64(u64 x, int n)
> {
>   return (x << (64-n)) >> (64-n);
> }
> 
> #define zex(x,y)						\
> 	((__typeof__(x))					\
> 	 (((__builtin_constant_p(y) && ((y) <= 32)) ||		\
> 	   (sizeof(x) <= sizeof(u32)))				\
> 	  ? zex32((x),(y)) : zex64((x),(y))))
> 

[PATCH 1/3] futex: remove duplicated code

[H. Peter Anvin]

<davem at davemloft.net>,Chris Metcalf <cmetcalf at mellanox.com>,Thomas Gleixner <tglx at linutronix.de>,Ingo Molnar <mingo at redhat.com>,Chris Zankel <chris at zankel.net>,Max Filippov <jcmvbkbc at gmail.com>,Arnd Bergmann <arnd at arndb.de>,x86 at kernel.org,linux-alpha at vger.kernel.org,linux-snps-arc at lists.infradead.org,linux-arm-kernel at lists.infradead.org,linux-hexagon at vger.kernel.org,linux-ia64 at vger.kernel.org,linux-mips at linux-mips.org,openrisc at lists.librecores.org,linux-parisc at vger.kernel.org,linuxppc-dev at lists.ozlabs.org,linux-s390 at vger.kernel.org,linux-sh at vger.kernel.org,sparclinux at vger.kernel.org,linux-xtensa at linux-xtensa.org,linux-arch at vger.kernel.org
From: hpa@zytor.com
List-ID: <linux-snps-arc@lists.infradead.org>
To: linux-snps-arc@lists.infradead.org
Message-ID: <9B46AFA6-C422-41FD-8E8A-356E44A6DCD2 at zytor.com>

On March 4, 2017 1:38:05 PM PST, Stafford Horne <shorne@gmail.com> wrote:
>On Sat, Mar 04, 2017@11:15:17AM -0800, H. Peter Anvin wrote:
>> On 03/04/17 05:05, Russell King - ARM Linux wrote:
>> >>  
>> >> +static int futex_atomic_op_inuser(int encoded_op, u32 __user
>*uaddr)
>> >> +{
>> >> +	int op = (encoded_op >> 28) & 7;
>> >> +	int cmp = (encoded_op >> 24) & 15;
>> >> +	int oparg = (encoded_op << 8) >> 20;
>> >> +	int cmparg = (encoded_op << 20) >> 20;
>> > 
>> > Hmm.  oparg and cmparg look like they're doing these shifts to get
>sign
>> > extension of the 12-bit values by assuming that "int" is 32-bit -
>> > probably worth a comment, or for safety, they should be "s32" so
>it's
>> > not dependent on the bit-width of "int".
>> > 
>> 
>> For readability, perhaps we should make sign- and zero-extension an
>> explicit facility?
>
>There is some of this in already here, 32 and 64 bit versions:
>
>  include/linux/bitops.h
>
>Do we really need zero extension? It seems the same.
>
>Example implementation from bitops.h
>
>static inline __s32 sign_extend32(__u32 value, int index)
>{
>        __u8 shift = 31 - index;
>        return (__s32)(value << shift) >> shift;
>}
>
>> /*
>>  * Truncate an integer x to n bits, using sign- or
>>  * zero-extension, respectively.
>>  */
>> static inline __const_func__ s32 sex32(s32 x, int n)
>> {
>>   return (x << (32-n)) >> (32-n);
>> }
>> 
>> static inline __const_func__ s64 sex64(s64 x, int n)
>> {
>>   return (x << (64-n)) >> (64-n);
>> }
>> 
>> #define sex(x,y)						\
>> 	((__typeof__(x))					\
>> 	 (((__builtin_constant_p(y) && ((y) <= 32)) ||		\
>> 	   (sizeof(x) <= sizeof(s32)))				\
>> 	  ? sex32((x),(y)) : sex64((x),(y))))
>> 
>> static inline __const_func__ u32 zex32(u32 x, int n)
>> {
>>   return (x << (32-n)) >> (32-n);
>> }
>> 
>> static inline __const_func__ u64 zex64(u64 x, int n)
>> {
>>   return (x << (64-n)) >> (64-n);
>> }
>> 
>> #define zex(x,y)						\
>> 	((__typeof__(x))					\
>> 	 (((__builtin_constant_p(y) && ((y) <= 32)) ||		\
>> 	   (sizeof(x) <= sizeof(u32)))				\
>> 	  ? zex32((x),(y)) : zex64((x),(y))))
>> 

Signed versus unsigned...
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

[PATCH 1/3] futex: remove duplicated code

[H. Peter Anvin]

<davem at davemloft.net>,Chris Metcalf <cmetcalf at mellanox.com>,Thomas Gleixner <tglx at linutronix.de>,Ingo Molnar <mingo at redhat.com>,Chris Zankel <chris at zankel.net>,Max Filippov <jcmvbkbc at gmail.com>,Arnd Bergmann <arnd at arndb.de>,x86 at kernel.org,linux-alpha at vger.kernel.org,linux-snps-arc at lists.infradead.org,linux-arm-kernel at lists.infradead.org,linux-hexagon at vger.kernel.org,linux-ia64 at vger.kernel.org,linux-mips at linux-mips.org,openrisc at lists.librecores.org,linux-parisc at vger.kernel.org,linuxppc-dev at lists.ozlabs.org,linux-s390 at vger.kernel.org,linux-sh at vger.kernel.org,sparclinux at vger.kernel.org,linux-xtensa at linux-xtensa.org,linux-arch at vger.kernel.org
From: hpa@zytor.com
List-ID: <linux-snps-arc@lists.infradead.org>
To: linux-snps-arc@lists.infradead.org
Message-ID: <CF18535E-39E7-44D3-88D0-80B9961E6681 at zytor.com>

On March 4, 2017 1:38:05 PM PST, Stafford Horne <shorne@gmail.com> wrote:
>On Sat, Mar 04, 2017@11:15:17AM -0800, H. Peter Anvin wrote:
>> On 03/04/17 05:05, Russell King - ARM Linux wrote:
>> >>  
>> >> +static int futex_atomic_op_inuser(int encoded_op, u32 __user
>*uaddr)
>> >> +{
>> >> +	int op = (encoded_op >> 28) & 7;
>> >> +	int cmp = (encoded_op >> 24) & 15;
>> >> +	int oparg = (encoded_op << 8) >> 20;
>> >> +	int cmparg = (encoded_op << 20) >> 20;
>> > 
>> > Hmm.  oparg and cmparg look like they're doing these shifts to get
>sign
>> > extension of the 12-bit values by assuming that "int" is 32-bit -
>> > probably worth a comment, or for safety, they should be "s32" so
>it's
>> > not dependent on the bit-width of "int".
>> > 
>> 
>> For readability, perhaps we should make sign- and zero-extension an
>> explicit facility?
>
>There is some of this in already here, 32 and 64 bit versions:
>
>  include/linux/bitops.h
>
>Do we really need zero extension? It seems the same.
>
>Example implementation from bitops.h
>
>static inline __s32 sign_extend32(__u32 value, int index)
>{
>        __u8 shift = 31 - index;
>        return (__s32)(value << shift) >> shift;
>}
>
>> /*
>>  * Truncate an integer x to n bits, using sign- or
>>  * zero-extension, respectively.
>>  */
>> static inline __const_func__ s32 sex32(s32 x, int n)
>> {
>>   return (x << (32-n)) >> (32-n);
>> }
>> 
>> static inline __const_func__ s64 sex64(s64 x, int n)
>> {
>>   return (x << (64-n)) >> (64-n);
>> }
>> 
>> #define sex(x,y)						\
>> 	((__typeof__(x))					\
>> 	 (((__builtin_constant_p(y) && ((y) <= 32)) ||		\
>> 	   (sizeof(x) <= sizeof(s32)))				\
>> 	  ? sex32((x),(y)) : sex64((x),(y))))
>> 
>> static inline __const_func__ u32 zex32(u32 x, int n)
>> {
>>   return (x << (32-n)) >> (32-n);
>> }
>> 
>> static inline __const_func__ u64 zex64(u64 x, int n)
>> {
>>   return (x << (64-n)) >> (64-n);
>> }
>> 
>> #define zex(x,y)						\
>> 	((__typeof__(x))					\
>> 	 (((__builtin_constant_p(y) && ((y) <= 32)) ||		\
>> 	   (sizeof(x) <= sizeof(u32)))				\
>> 	  ? zex32((x),(y)) : zex64((x),(y))))
>> 

Also, i strongly believe that making it syntactically cumbersome encodes people to open-code it which is bad...
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

[PATCH 1/3] futex: remove duplicated code

[Rob Landley]

On 03/04/2017 07:05 AM, Russell King - ARM Linux wrote:
> On Fri, Mar 03, 2017@01:27:10PM +0100, Jiri Slaby wrote:
>> diff --git a/kernel/futex.c b/kernel/futex.c
>> index b687cb22301c..c5ff9850952f 100644
>> --- a/kernel/futex.c
>> +++ b/kernel/futex.c
>> @@ -1457,6 +1457,42 @@ futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
>>  	return ret;
>>  }
>>  
>> +static int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
>> +{
>> +	int op = (encoded_op >> 28) & 7;
>> +	int cmp = (encoded_op >> 24) & 15;
>> +	int oparg = (encoded_op << 8) >> 20;
>> +	int cmparg = (encoded_op << 20) >> 20;
> 
> Hmm.  oparg and cmparg look like they're doing these shifts to get sign
> extension of the 12-bit values by assuming that "int" is 32-bit -
> probably worth a comment, or for safety, they should be "s32" so it's
> not dependent on the bit-width of "int".

I thought Linux depended on the LP64 standard for all architectures?

Standard: http://www.unix.org/whitepapers/64bit.html
Rationale: http://www.unix.org/version2/whatsnew/lp64_wp.html

So int has a defined bit width (32) on linux?

Rob

[PATCH 1/3] futex: remove duplicated code

[H. Peter Anvin]

<cmetcalf at mellanox.com>,Thomas Gleixner <tglx at linutronix.de>,Ingo Molnar <mingo at redhat.com>,Chris Zankel <chris at zankel.net>,Max Filippov <jcmvbkbc at gmail.com>,Arnd Bergmann <arnd at arndb.de>,x86 at kernel.org,linux-alpha at vger.kernel.org,linux-snps-arc at lists.infradead.org,linux-arm-kernel at lists.infradead.org,linux-hexagon at vger.kernel.org,linux-ia64 at vger.kernel.org,linux-mips at linux-mips.org,openrisc at lists.librecores.org,linux-parisc at vger.kernel.org,linuxppc-dev at lists.ozlabs.org,linux-s390 at vger.kernel.org,linux-sh at vger.kernel.org,sparclinux at vger.kernel.org,linux-xtensa at linux-xtensa.org,linux-arch at vger.kernel.org
From: hpa@zytor.com
List-ID: <linux-snps-arc@lists.infradead.org>
To: linux-snps-arc@lists.infradead.org
Message-ID: <83324528-AAA1-4BED-B0C7-48426ECBA261 at zytor.com>

On March 8, 2017 8:16:49 PM PST, Rob Landley <rob@landley.net> wrote:
>On 03/04/2017 07:05 AM, Russell King - ARM Linux wrote:
>> On Fri, Mar 03, 2017@01:27:10PM +0100, Jiri Slaby wrote:
>>> diff --git a/kernel/futex.c b/kernel/futex.c
>>> index b687cb22301c..c5ff9850952f 100644
>>> --- a/kernel/futex.c
>>> +++ b/kernel/futex.c
>>> @@ -1457,6 +1457,42 @@ futex_wake(u32 __user *uaddr, unsigned int
>flags, int nr_wake, u32 bitset)
>>>  	return ret;
>>>  }
>>>  
>>> +static int futex_atomic_op_inuser(int encoded_op, u32 __user
>*uaddr)
>>> +{
>>> +	int op = (encoded_op >> 28) & 7;
>>> +	int cmp = (encoded_op >> 24) & 15;
>>> +	int oparg = (encoded_op << 8) >> 20;
>>> +	int cmparg = (encoded_op << 20) >> 20;
>> 
>> Hmm.  oparg and cmparg look like they're doing these shifts to get
>sign
>> extension of the 12-bit values by assuming that "int" is 32-bit -
>> probably worth a comment, or for safety, they should be "s32" so it's
>> not dependent on the bit-width of "int".
>
>I thought Linux depended on the LP64 standard for all architectures?
>
>Standard: http://www.unix.org/whitepapers/64bit.html
>Rationale: http://www.unix.org/version2/whatsnew/lp64_wp.html
>
>So int has a defined bit width (32) on linux?
>
>Rob

Linux is ILP32 on 32-bit architectures and LP64 on 64-bit architectures, but that doesn't inherently make this stuff clear.
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

[PATCH 1/3] futex: remove duplicated code

[Rich Felker]

On Fri, Mar 03, 2017@01:27:10PM +0100, Jiri Slaby wrote:
> There is code duplicated over all architecture's headers for
> futex_atomic_op_inuser. Namely op decoding, access_ok check for uaddr,
> and comparison of the result.
> 
> Remove this duplication and leave up to the arches only the needed
> assembly which is now in arch_futex_atomic_op_inuser.
> 
> Note that s390 removed access_ok check in d12a29703 ("s390/uaccess:
> remove pointless access_ok() checks") as access_ok there returns true.
> We introduce it back to the helper for the sake of simplicity (it gets
> optimized away anyway).

Overall I'm in favor of this patch, and it's close to what I had in
mind in the commit message for
00b73d8d1b7131da03aec73011a7286f566fe87f. But I'd actually like to see
it go further. These ops are mainly (only?) used for the (almost never
used) FUTEX_WAKE_OP operation, and there's very little sense in trying
to optimize them with dedicated arch-specific forms like "lock xadd".
Instead the entire logic should be in an arch-generic file, and all
the arch should need to provide is a cmpxchg-on-user-memory primitive
for it to use. On most archs, the same cmpxchg used in kernelspace
should also work for user addresses, meaning a huge amount of
unmaintained, largely untested, junk code can be removed.

Rich