From 4cca2ab319b9cea1a31d8e8b579946da549928dd Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Mon, 11 May 2015 17:52:17 +0200 Subject: [PATCH 12/14] futex: clarify that preemption doesn't have to be disabled Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.0/patches-4.0.4-rt1.tar.xz As arm64 and arc have no special implementations for !CONFIG_SMP, mutual exclusion doesn't seem to rely on preemption. Let's make it clear in the comments that preemption doesn't have to be disabled when accessing user space in the futex code, so we can remove preempt_disable() from pagefault_disable(). Signed-off-by: David Hildenbrand --- arch/arc/include/asm/futex.h | 10 +++++----- arch/arm64/include/asm/futex.h | 4 ++-- 2 files changed, 7 insertions(+), 7 deletions(-) --- a/arch/arc/include/asm/futex.h +++ b/arch/arc/include/asm/futex.h @@ -53,7 +53,7 @@ static inline int futex_atomic_op_inuser if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int))) return -EFAULT; - pagefault_disable(); /* implies preempt_disable() */ + pagefault_disable(); switch (op) { case FUTEX_OP_SET: @@ -75,7 +75,7 @@ static inline int futex_atomic_op_inuser ret = -ENOSYS; } - pagefault_enable(); /* subsumes preempt_enable() */ + pagefault_enable(); if (!ret) { switch (cmp) { @@ -104,7 +104,7 @@ static inline int futex_atomic_op_inuser return ret; } -/* Compare-xchg with preemption disabled. +/* Compare-xchg with pagefaults disabled. * Notes: * -Best-Effort: Exchg happens only if compare succeeds. * If compare fails, returns; leaving retry/looping to upper layers @@ -121,7 +121,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int))) return -EFAULT; - pagefault_disable(); /* implies preempt_disable() */ + pagefault_disable(); /* TBD : can use llock/scond */ __asm__ __volatile__( @@ -142,7 +142,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, : "r"(oldval), "r"(newval), "r"(uaddr), "ir"(-EFAULT) : "cc", "memory"); - pagefault_enable(); /* subsumes preempt_enable() */ + pagefault_enable(); *uval = val; return val; --- a/arch/arm64/include/asm/futex.h +++ b/arch/arm64/include/asm/futex.h @@ -58,7 +58,7 @@ futex_atomic_op_inuser (int encoded_op, if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))) return -EFAULT; - pagefault_disable(); /* implies preempt_disable() */ + pagefault_disable(); switch (op) { case FUTEX_OP_SET: @@ -85,7 +85,7 @@ futex_atomic_op_inuser (int encoded_op, ret = -ENOSYS; } - pagefault_enable(); /* subsumes preempt_enable() */ + pagefault_enable(); if (!ret) { switch (cmp) {