[PATCH v2] treewide: get rid of HAVE_FUTEX_CMPXCHG

From: Max Filippov <jcmvbkbc@gmail.com>
To: LKML <linux-kernel@vger.kernel.org>
Cc: linux-arch@vger.kernel.org, Max Filippov <jcmvbkbc@gmail.com>,
	Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Paul Burton <paul.burton@mips.com>,
	Ralf Baechle <ralf@linux-mips.org>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: [PATCH v2] treewide: get rid of HAVE_FUTEX_CMPXCHG
Date: Fri, 25 Jan 2019 10:46:40 -0800	[thread overview]
Message-ID: <20190125184640.5174-1-jcmvbkbc@gmail.com> (raw)

CONFIG_HAVE_FUTEX_CMPXCHG is currently used to determine if
atomic_inatomic is always working or must be probed. For most
architectures it is either selected, or it is known that they always
have futex_atomic_cmpxchg_inatomic working.

Drop HAVE_FUTEX_CMPXCHG from the Kconfig and let architectures that may
not have it working define macro arch_have_futex_cmpxchg that probes
whether futex_atomic_cmpxchg_inatomic is working, otherwise assume that
it is working.

Implement arch_have_futex_cmpxchg for MIPS, Xtensa and for the users of
asm-generic/futex.h.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
Changes v1->v2:
- fix #ifdef/#ifndef logic in kernel/futex.c

 arch/arc/Kconfig                |  1 -
 arch/m68k/Kconfig               |  1 -
 arch/mips/include/asm/futex.h   |  2 ++
 arch/riscv/Kconfig              |  1 -
 arch/s390/Kconfig               |  1 -
 arch/sh/Kconfig                 |  1 -
 arch/um/Kconfig                 |  1 -
 arch/xtensa/Kconfig             |  1 -
 arch/xtensa/include/asm/futex.h |  4 ++++
 include/asm-generic/futex.h     |  2 ++
 init/Kconfig                    |  8 --------
 kernel/futex.c                  | 30 ++++++++----------------------
 12 files changed, 16 insertions(+), 37 deletions(-)

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 376366a7db81..01932be9f7e3 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -29,7 +29,6 @@ config ARC
 	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_DEBUG_STACKOVERFLOW
-	select HAVE_FUTEX_CMPXCHG if FUTEX
 	select HAVE_GENERIC_DMA_COHERENT
 	select HAVE_IOREMAP_PROT
 	select HAVE_KERNEL_GZIP
diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
index e173ea2ff395..09499af5d22a 100644
--- a/arch/m68k/Kconfig
+++ b/arch/m68k/Kconfig
@@ -20,7 +20,6 @@ config M68K
 	select GENERIC_STRNLEN_USER if MMU
 	select ARCH_WANT_IPC_PARSE_VERSION
 	select ARCH_USES_GETTIMEOFFSET if MMU && !COLDFIRE
-	select HAVE_FUTEX_CMPXCHG if MMU && FUTEX
 	select HAVE_MOD_ARCH_SPECIFIC
 	select MODULES_USE_ELF_REL
 	select MODULES_USE_ELF_RELA
diff --git a/arch/mips/include/asm/futex.h b/arch/mips/include/asm/futex.h
index c14d798f3888..f61221d080fc 100644
--- a/arch/mips/include/asm/futex.h
+++ b/arch/mips/include/asm/futex.h
@@ -122,6 +122,8 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
 	return ret;
 }
 
+#define arch_have_futex_cmpxchg() (cpu_has_llsc)
+
 static inline int
 futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 			      u32 oldval, u32 newval)
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index feeeaa60697c..074966cdd41d 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -31,7 +31,6 @@ config RISCV
 	select HAVE_ARCH_AUDITSYSCALL
 	select HAVE_MEMBLOCK_NODE_MAP
 	select HAVE_DMA_CONTIGUOUS
-	select HAVE_FUTEX_CMPXCHG if FUTEX
 	select HAVE_GENERIC_DMA_COHERENT
 	select HAVE_PERF_EVENTS
 	select HAVE_SYSCALL_TRACEPOINTS
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index ed554b09eb3f..6f3819275d08 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -146,7 +146,6 @@ config S390
 	select HAVE_FTRACE_MCOUNT_RECORD
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_TRACER
-	select HAVE_FUTEX_CMPXCHG if FUTEX
 	select HAVE_GCC_PLUGINS
 	select HAVE_KERNEL_BZIP2
 	select HAVE_KERNEL_GZIP
diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index a9c36f95744a..a04bc11c8819 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -50,7 +50,6 @@ config SUPERH
 	select OLD_SIGACTION
 	select PCI_DOMAINS if PCI
 	select HAVE_ARCH_AUDITSYSCALL
-	select HAVE_FUTEX_CMPXCHG if FUTEX
 	select HAVE_NMI
 	select NEED_SG_DMA_LENGTH
 
diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index ec9711d068b7..38c5ce3b64b1 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -10,7 +10,6 @@ config UML
 	select HAVE_ARCH_AUDITSYSCALL
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_UID16
-	select HAVE_FUTEX_CMPXCHG if FUTEX
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DEBUG_BUGVERBOSE
 	select GENERIC_IRQ_SHOW
diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index 7021d1e15909..a4d34de57809 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -25,7 +25,6 @@ config XTENSA
 	select HAVE_DMA_CONTIGUOUS
 	select HAVE_EXIT_THREAD
 	select HAVE_FUNCTION_TRACER
-	select HAVE_FUTEX_CMPXCHG if !MMU
 	select HAVE_HW_BREAKPOINT if PERF_EVENTS
 	select HAVE_IRQ_TIME_ACCOUNTING
 	select HAVE_OPROFILE
diff --git a/arch/xtensa/include/asm/futex.h b/arch/xtensa/include/asm/futex.h
index 505d09eff184..ac88d64f94e4 100644
--- a/arch/xtensa/include/asm/futex.h
+++ b/arch/xtensa/include/asm/futex.h
@@ -87,6 +87,10 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
 	return ret;
 }
 
+#if !XCHAL_HAVE_S32C1I
+#define arch_have_futex_cmpxchg() (0)
+#endif
+
 static inline int
 futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 			      u32 oldval, u32 newval)
diff --git a/include/asm-generic/futex.h b/include/asm-generic/futex.h
index fcb61b4659b3..deefe5b22b9b 100644
--- a/include/asm-generic/futex.h
+++ b/include/asm-generic/futex.h
@@ -136,6 +136,8 @@ arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)
 	return ret;
 }
 
+#define arch_have_futex_cmpxchg() (0)
+
 static inline int
 futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 			      u32 oldval, u32 newval)
diff --git a/init/Kconfig b/init/Kconfig
index 513fa544a134..351f4c93f932 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1338,14 +1338,6 @@ config FUTEX_PI
 	depends on FUTEX && RT_MUTEXES
 	default y
 
-config HAVE_FUTEX_CMPXCHG
-	bool
-	depends on FUTEX
-	help
-	  Architectures should select this if futex_atomic_cmpxchg_inatomic()
-	  is implemented and always working. This removes a couple of runtime
-	  checks.
-
 config EPOLL
 	bool "Enable eventpoll support" if EXPERT
 	default y
diff --git a/kernel/futex.c b/kernel/futex.c
index be3bff2315ff..1b3695c4c6cc 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -174,7 +174,11 @@
  * double_lock_hb() and double_unlock_hb(), respectively.
  */
 
-#ifdef CONFIG_HAVE_FUTEX_CMPXCHG
+/*
+ * Architectures should define this macro if futex_atomic_cmpxchg_inatomic()
+ * may not be always working.
+ */
+#ifndef arch_have_futex_cmpxchg
 #define futex_cmpxchg_enabled 1
 #else
 static int  __read_mostly futex_cmpxchg_enabled;
@@ -3842,26 +3846,6 @@ COMPAT_SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
 }
 #endif /* CONFIG_COMPAT_32BIT_TIME */
 
-static void __init futex_detect_cmpxchg(void)
-{
-#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
-	u32 curval;
-
-	/*
-	 * This will fail and we want it. Some arch implementations do
-	 * runtime detection of the futex_atomic_cmpxchg_inatomic()
-	 * functionality. We want to know that before we call in any
-	 * of the complex code paths. Also we want to prevent
-	 * registration of robust lists in that case. NULL is
-	 * guaranteed to fault and we get -EFAULT on functional
-	 * implementation, the non-functional ones will return
-	 * -ENOSYS.
-	 */
-	if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
-		futex_cmpxchg_enabled = 1;
-#endif
-}
-
 static int __init futex_init(void)
 {
 	unsigned int futex_shift;
@@ -3880,7 +3864,9 @@ static int __init futex_init(void)
 					       futex_hashsize, futex_hashsize);
 	futex_hashsize = 1UL << futex_shift;
 
-	futex_detect_cmpxchg();
+#ifdef arch_have_futex_cmpxchg
+	futex_cmpxchg_enabled = arch_have_futex_cmpxchg();
+#endif
 
 	for (i = 0; i < futex_hashsize; i++) {
 		atomic_set(&futex_queues[i].waiters, 0);
-- 
2.11.0

