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Subject[patch v2 3/4] percpu_counter: fix code for 32bit systems
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 | 48 ++++++++++++++++++++++++++++++-----------
1 file changed, 36 insertions(+), 12 deletions(-)

Index: linux/include/linux/percpu_counter.h
===================================================================
--- linux.orig/include/linux/percpu_counter.h 2011-04-13 13:21:21.000000000 +0800
+++ linux/include/linux/percpu_counter.h 2011-04-13 13:27:22.000000000 +0800
@@ -60,7 +60,16 @@ static inline s64 percpu_counter_sum(str

static inline s64 percpu_counter_read(struct percpu_counter *fbc)
{
+#if BITS_PER_LONG == 32
+ s64 count;
+ unsigned long flags;
+ spin_lock_irqsave(&fbc->lock, flags);
+ count = fbc->count;
+ spin_unlock_irqrestore(&fbc->lock, flags);
+ return count;
+#else
return fbc->count;
+#endif
}

/*
@@ -70,7 +79,7 @@ static inline s64 percpu_counter_read(st
*/
static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
{
- s64 ret = fbc->count;
+ s64 ret = percpu_counter_read(fbc);

barrier(); /* Prevent reloads of fbc->count */
if (ret >= 0)
@@ -89,9 +98,20 @@ 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 +119,25 @@ 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 +157,13 @@ __percpu_counter_add(struct percpu_count
percpu_counter_add(fbc, amount);
}

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

static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)


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