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