Re: [PATCH 2/2] futex: remove futex_cmpxchg detection
From: Christian Borntraeger
Date: Tue Oct 26 2021 - 06:45:07 EST
Am 26.10.21 um 12:03 schrieb Arnd Bergmann:
From: Arnd Bergmann <arnd@xxxxxxxx>
Now that all architectures have a working futex implementation
in any configuration, remove the runtime detection code.
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
s390 part
Acked-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
---
arch/arc/Kconfig | 1 -
arch/arm/Kconfig | 1 -
arch/arm64/Kconfig | 1 -
arch/csky/Kconfig | 1 -
arch/m68k/Kconfig | 1 -
arch/riscv/Kconfig | 1 -
arch/s390/Kconfig | 1 -
arch/sh/Kconfig | 1 -
arch/um/Kconfig | 1 -
arch/um/kernel/skas/uaccess.c | 1 -
arch/xtensa/Kconfig | 1 -
init/Kconfig | 8 --------
kernel/futex/core.c | 35 -----------------------------------
kernel/futex/futex.h | 6 ------
kernel/futex/syscalls.c | 22 ----------------------
15 files changed, 82 deletions(-)
diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 248389278e8f..f9413041686f 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -31,7 +31,6 @@ config ARC
select HAVE_ARCH_TRANSPARENT_HUGEPAGE if ARC_MMU_V4
select HAVE_DEBUG_STACKOVERFLOW
select HAVE_DEBUG_KMEMLEAK
- select HAVE_FUTEX_CMPXCHG if FUTEX
select HAVE_IOREMAP_PROT
select HAVE_KERNEL_GZIP
select HAVE_KERNEL_LZMA
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index bb5d2c45477b..6448d311635d 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -93,7 +93,6 @@ config ARM
select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL && !CC_IS_CLANG
select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !(THUMB2_KERNEL && CC_IS_CLANG)
- select HAVE_FUTEX_CMPXCHG if FUTEX
select HAVE_GCC_PLUGINS
select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7)
select HAVE_IRQ_TIME_ACCOUNTING
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 0efc501f77aa..6c3c2ff5cef8 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -193,7 +193,6 @@ config ARM64
select HAVE_PERF_USER_STACK_DUMP
select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_FUNCTION_ARG_ACCESS_API
- select HAVE_FUTEX_CMPXCHG if FUTEX
select MMU_GATHER_RCU_TABLE_FREE
select HAVE_RSEQ
select HAVE_STACKPROTECTOR
diff --git a/arch/csky/Kconfig b/arch/csky/Kconfig
index 823d3d5a9e11..efd7c5feac8b 100644
--- a/arch/csky/Kconfig
+++ b/arch/csky/Kconfig
@@ -53,7 +53,6 @@ config CSKY
select HAVE_FUNCTION_TRACER
select HAVE_FUNCTION_GRAPH_TRACER
select HAVE_FUNCTION_ERROR_INJECTION
- select HAVE_FUTEX_CMPXCHG if FUTEX && SMP
select HAVE_FTRACE_MCOUNT_RECORD
select HAVE_KERNEL_GZIP
select HAVE_KERNEL_LZO
diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
index 0b50da08a9c5..15a793c5b2dc 100644
--- a/arch/m68k/Kconfig
+++ b/arch/m68k/Kconfig
@@ -20,7 +20,6 @@ config M68K
select HAVE_ASM_MODVERSIONS
select HAVE_DEBUG_BUGVERBOSE
select HAVE_EFFICIENT_UNALIGNED_ACCESS if !CPU_HAS_NO_UNALIGNED
- select HAVE_FUTEX_CMPXCHG if MMU && FUTEX
select HAVE_MOD_ARCH_SPECIFIC
select HAVE_UID16
select MMU_GATHER_NO_RANGE if MMU
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 77a088d0a7e9..037fea9fac14 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -84,7 +84,6 @@ config RISCV
select HAVE_DMA_CONTIGUOUS if MMU
select HAVE_EBPF_JIT if MMU
select HAVE_FUNCTION_ERROR_INJECTION
- select HAVE_FUTEX_CMPXCHG if FUTEX
select HAVE_GCC_PLUGINS
select HAVE_GENERIC_VDSO if MMU && 64BIT
select HAVE_IRQ_TIME_ACCOUNTING
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index f615c3f65f5a..1c9ecf619e04 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -164,7 +164,6 @@ config S390
select HAVE_FUNCTION_ERROR_INJECTION
select HAVE_FUNCTION_GRAPH_TRACER
select HAVE_FUNCTION_TRACER
- select HAVE_FUTEX_CMPXCHG if FUTEX
select HAVE_GCC_PLUGINS
select HAVE_GENERIC_VDSO
select HAVE_IOREMAP_PROT if PCI
diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index 6904f4bdbf00..93195d3368c0 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -34,7 +34,6 @@ config SUPERH
select HAVE_FAST_GUP if MMU
select HAVE_FUNCTION_GRAPH_TRACER
select HAVE_FUNCTION_TRACER
- select HAVE_FUTEX_CMPXCHG if FUTEX
select HAVE_FTRACE_MCOUNT_RECORD
select HAVE_HW_BREAKPOINT
select HAVE_IOREMAP_PROT if MMU && !X2TLB
diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index c18b45f75d41..c906250d4970 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -14,7 +14,6 @@ config UML
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ASM_MODVERSIONS
select HAVE_UID16
- select HAVE_FUTEX_CMPXCHG if FUTEX
select HAVE_DEBUG_KMEMLEAK
select HAVE_DEBUG_BUGVERBOSE
select NO_DMA if !UML_DMA_EMULATION
diff --git a/arch/um/kernel/skas/uaccess.c b/arch/um/kernel/skas/uaccess.c
index a509be911026..9e37a7c05990 100644
--- a/arch/um/kernel/skas/uaccess.c
+++ b/arch/um/kernel/skas/uaccess.c
@@ -348,7 +348,6 @@ EXPORT_SYMBOL(arch_futex_atomic_op_inuser);
* 0 - On success
* -EFAULT - User access resulted in a page fault
* -EAGAIN - Atomic operation was unable to complete due to contention
- * -ENOSYS - Function not implemented (only if !HAVE_FUTEX_CMPXCHG)
*/
int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index 0e56bad058fa..8ac599aa6d99 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -31,7 +31,6 @@ config XTENSA
select HAVE_DMA_CONTIGUOUS
select HAVE_EXIT_THREAD
select HAVE_FUNCTION_TRACER
- select HAVE_FUTEX_CMPXCHG if !MMU && FUTEX
select HAVE_HW_BREAKPOINT if PERF_EVENTS
select HAVE_IRQ_TIME_ACCOUNTING
select HAVE_PCI
diff --git a/init/Kconfig b/init/Kconfig
index c0f55ea5a71f..538688598f2f 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1597,14 +1597,6 @@ 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/core.c b/kernel/futex/core.c
index 25d8a88b32e5..926c2bb752bc 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -41,11 +41,6 @@
#include "futex.h"
#include "../locking/rtmutex_common.h"
-#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
-int __read_mostly futex_cmpxchg_enabled;
-#endif
-
-
/*
* The base of the bucket array and its size are always used together
* (after initialization only in futex_hash()), so ensure that they
@@ -776,9 +771,6 @@ static void exit_robust_list(struct task_struct *curr)
unsigned long futex_offset;
int rc;
- if (!futex_cmpxchg_enabled)
- return;
-
/*
* Fetch the list head (which was registered earlier, via
* sys_set_robust_list()):
@@ -874,9 +866,6 @@ static void compat_exit_robust_list(struct task_struct *curr)
compat_long_t futex_offset;
int rc;
- if (!futex_cmpxchg_enabled)
- return;
-
/*
* Fetch the list head (which was registered earlier, via
* sys_set_robust_list()):
@@ -950,8 +939,6 @@ static void exit_pi_state_list(struct task_struct *curr)
struct futex_hash_bucket *hb;
union futex_key key = FUTEX_KEY_INIT;
- if (!futex_cmpxchg_enabled)
- return;
/*
* We are a ZOMBIE and nobody can enqueue itself on
* pi_state_list anymore, but we have to be careful
@@ -1125,26 +1112,6 @@ void futex_exit_release(struct task_struct *tsk)
futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
}
-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 (futex_cmpxchg_value_locked(&curval, NULL, 0, 0) == -EFAULT)
- futex_cmpxchg_enabled = 1;
-#endif
-}
-
static int __init futex_init(void)
{
unsigned int futex_shift;
@@ -1163,8 +1130,6 @@ static int __init futex_init(void)
futex_hashsize, futex_hashsize);
futex_hashsize = 1UL << futex_shift;
- futex_detect_cmpxchg();
-
for (i = 0; i < futex_hashsize; i++) {
atomic_set(&futex_queues[i].waiters, 0);
plist_head_init(&futex_queues[i].chain);
diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
index 040ae4277cb0..c264cbeab71c 100644
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -27,12 +27,6 @@
#define FLAGS_CLOCKRT 0x02
#define FLAGS_HAS_TIMEOUT 0x04
-#ifdef CONFIG_HAVE_FUTEX_CMPXCHG
-#define futex_cmpxchg_enabled 1
-#else
-extern int __read_mostly futex_cmpxchg_enabled;
-#endif
-
#ifdef CONFIG_FAIL_FUTEX
extern bool should_fail_futex(bool fshared);
#else
diff --git a/kernel/futex/syscalls.c b/kernel/futex/syscalls.c
index 6f91a07a6a83..086a22d1adb7 100644
--- a/kernel/futex/syscalls.c
+++ b/kernel/futex/syscalls.c
@@ -29,8 +29,6 @@
SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
size_t, len)
{
- if (!futex_cmpxchg_enabled)
- return -ENOSYS;
/*
* The kernel knows only one size for now:
*/
@@ -56,9 +54,6 @@ SYSCALL_DEFINE3(get_robust_list, int, pid,
unsigned long ret;
struct task_struct *p;
- if (!futex_cmpxchg_enabled)
- return -ENOSYS;
-
rcu_read_lock();
ret = -ESRCH;
@@ -103,17 +98,6 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
return -ENOSYS;
}
- switch (cmd) {
- case FUTEX_LOCK_PI:
- case FUTEX_LOCK_PI2:
- case FUTEX_UNLOCK_PI:
- case FUTEX_TRYLOCK_PI:
- case FUTEX_WAIT_REQUEUE_PI:
- case FUTEX_CMP_REQUEUE_PI:
- if (!futex_cmpxchg_enabled)
- return -ENOSYS;
- }
-
switch (cmd) {
case FUTEX_WAIT:
val3 = FUTEX_BITSET_MATCH_ANY;
@@ -323,9 +307,6 @@ COMPAT_SYSCALL_DEFINE2(set_robust_list,
struct compat_robust_list_head __user *, head,
compat_size_t, len)
{
- if (!futex_cmpxchg_enabled)
- return -ENOSYS;
-
if (unlikely(len != sizeof(*head)))
return -EINVAL;
@@ -342,9 +323,6 @@ COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
unsigned long ret;
struct task_struct *p;
- if (!futex_cmpxchg_enabled)
- return -ENOSYS;
-
rcu_read_lock();
ret = -ESRCH;