Messages in this thread Patch in this message | | | Subject | Re: [patch v3 2/3] percpu_counter: fix code for 32bit systems for UP | From | Shaohua Li <> | Date | Mon, 18 Apr 2011 15:41:32 +0800 |
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On Thu, 2011-04-14 at 10:54 +0800, Eric Dumazet wrote: > Le jeudi 14 avril 2011 à 10:44 +0800, Shaohua Li a écrit : > > that's true. I just want the code looks consistent and this doesn't > > really obfuscate the code to me. > > Doing so gives a false sense of security to user. > > percpu_counter_init() is unsafe by nature. I really don't think this matters, but since you insist, here is the updated the patch.
Subject: 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 | 31 +++++++++++++++++++++++-------- 1 file changed, 23 insertions(+), 8 deletions(-)
Index: linux/include/linux/percpu_counter.h =================================================================== --- linux.orig/include/linux/percpu_counter.h 2011-04-18 15:36:31.000000000 +0800 +++ linux/include/linux/percpu_counter.h 2011-04-18 15:37:35.000000000 +0800 @@ -101,14 +101,34 @@ static inline void percpu_counter_destro 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 s64 percpu_counter_read(struct percpu_counter *fbc) +{ +#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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