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futex: Remove futex_cmpxchg detection
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Now that all architectures have a working futex implementation in any
configuration, remove the runtime detection code.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Acked-by: Vineet Gupta <vgupta@kernel.org>
Acked-by: Max Filippov <jcmvbkbc@gmail.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Link: https://lore.kernel.org/r/20211026100432.1730393-2-arnd@kernel.org
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@arndb @KAGA-KOKO
arndb authored and KAGA-KOKO committed Nov 24, 2021
1 parent 3f2beda commit 3297481
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Showing 15 changed files with 0 additions and 82 deletions.
1 change: 0 additions & 1 deletion arch/arc/Kconfig
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Expand Up @@ -32,7 +32,6 @@ 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
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1 change: 0 additions & 1 deletion arch/arm/Kconfig
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Expand Up @@ -92,7 +92,6 @@ 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
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1 change: 0 additions & 1 deletion arch/arm64/Kconfig
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Expand Up @@ -194,7 +194,6 @@ config ARM64
select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_POSIX_CPU_TIMERS_TASK_WORK
select HAVE_FUNCTION_ARG_ACCESS_API
select HAVE_FUTEX_CMPXCHG if FUTEX
select MMU_GATHER_RCU_TABLE_FREE
select HAVE_RSEQ
select HAVE_STACKPROTECTOR
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1 change: 0 additions & 1 deletion arch/csky/Kconfig
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Expand Up @@ -52,7 +52,6 @@ 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
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1 change: 0 additions & 1 deletion arch/m68k/Kconfig
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Expand Up @@ -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
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1 change: 0 additions & 1 deletion arch/riscv/Kconfig
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Expand Up @@ -83,7 +83,6 @@ 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
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1 change: 0 additions & 1 deletion arch/s390/Kconfig
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Expand Up @@ -165,7 +165,6 @@ 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
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1 change: 0 additions & 1 deletion arch/sh/Kconfig
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Expand Up @@ -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
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1 change: 0 additions & 1 deletion arch/um/Kconfig
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Expand Up @@ -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
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1 change: 0 additions & 1 deletion arch/um/kernel/skas/uaccess.c
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Expand Up @@ -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,
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1 change: 0 additions & 1 deletion arch/xtensa/Kconfig
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Expand Up @@ -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
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8 changes: 0 additions & 8 deletions init/Kconfig
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Expand Up @@ -1592,14 +1592,6 @@ 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
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35 changes: 0 additions & 35 deletions kernel/futex/core.c
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Expand Up @@ -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
Expand Down Expand Up @@ -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()):
Expand Down Expand Up @@ -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()):
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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;
Expand All @@ -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);
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6 changes: 0 additions & 6 deletions kernel/futex/futex.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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
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22 changes: 0 additions & 22 deletions kernel/futex/syscalls.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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:
*/
Expand All @@ -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;
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;

Expand All @@ -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;
Expand Down

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