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Subject[patch v3 2/3] percpu_counter: fix code for 32bit systems for UP
percpu_counter.counter is a 's64'. Accessing it in 32-bit system is racing.
we need some locking to protect it otherwise some very wrong value could be
accessed.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
---
include/linux/percpu_counter.h | 37 ++++++++++++++++++++++++++-----------
1 file changed, 26 insertions(+), 11 deletions(-)

Index: linux/include/linux/percpu_counter.h
===================================================================
--- linux.orig/include/linux/percpu_counter.h 2011-04-14 08:50:45.000000000 +0800
+++ linux/include/linux/percpu_counter.h 2011-04-14 09:09:14.000000000 +0800
@@ -89,9 +89,20 @@ struct percpu_counter {
s64 count;
};

-static inline int percpu_counter_init(struct percpu_counter *fbc, s64 amount)
+static inline void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
{
+#if BITS_PER_LONG == 32
+ preempt_disable();
fbc->count = amount;
+ preempt_enable();
+#else
+ fbc->count = amount;
+#endif
+}
+
+static inline int percpu_counter_init(struct percpu_counter *fbc, s64 amount)
+{
+ percpu_counter_set(fbc, amount);
return 0;
}

@@ -99,16 +110,25 @@ static inline void percpu_counter_destro
{
}

-static inline void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
+static inline s64 percpu_counter_read(struct percpu_counter *fbc)
{
- fbc->count = amount;
+#if BITS_PER_LONG == 32
+ s64 count;
+ preempt_disable();
+ count = fbc->count;
+ preempt_enable();
+ return count;
+#else
+ return fbc->count;
+#endif
}

static inline int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs)
{
- if (fbc->count > rhs)
+ s64 count = percpu_counter_read(fbc);
+ if (count > rhs)
return 1;
- else if (fbc->count < rhs)
+ else if (count < rhs)
return -1;
else
return 0;
@@ -128,18 +148,13 @@ __percpu_counter_add(struct percpu_count
percpu_counter_add(fbc, amount);
}

-static inline s64 percpu_counter_read(struct percpu_counter *fbc)
-{
- return fbc->count;
-}
-
/*
* percpu_counter is intended to track positive number. In UP case, the number
* should never be negative.
*/
static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
{
- return fbc->count;
+ return percpu_counter_read(fbc);
}

static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)


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