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Subject[PATCH v3 03/13] futex: Add helpers to get & cmpxchg futex value without lock
Date
Two new helper functions cmpxchg_futex_value() and get_futex_value()
are added to access and change the futex value without the hash
bucket lock. As a result, page fault is enabled and the page will
be faulted in if not present yet.

Signed-off-by: Waiman Long <Waiman.Long@hpe.com>
---
kernel/futex.c | 15 +++++++++++++++
1 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index f4e20ad..ebe59fa 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -794,6 +794,21 @@ static int get_futex_value_locked(u32 *dest, u32 __user *from)
return ret ? -EFAULT : 0;
}

+/*
+ * The equivalents of the above cmpxchg_futex_value_locked() and
+ * get_futex_value_locked which are called without the hash bucket lock
+ * and so can have page fault enabled.
+ */
+static inline int cmpxchg_futex_value(u32 *curval, u32 __user *uaddr,
+ u32 uval, u32 newval)
+{
+ return futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
+}
+
+static inline int get_futex_value(u32 *dest, u32 __user *from)
+{
+ return __get_user(*dest, from);
+}

/*
* PI code:
--
1.7.1
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