linux-ext4 - [PATCH] atomic: fix a typo in atomic_long

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Date:	Sun, 07 Dec 2008 23:24:29 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux kernel <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mingming Cao <cmm@...ibm.com>, "Theodore Ts'o" <tytso@....edu>,
	linux-ext4@...r.kernel.org
Subject: [PATCH] atomic: fix a typo in atomic_long_xchg()

Andrew Morton a écrit :
> We can do lots of things in 2.6.29.  Including just making ->counters
> an array of atomic_t.

I was playing with this idea this week (but using atomic_long_t),
and this is why I bother you with all this stuff : cleanup patches
before work for 2.6.29

My idea was using atomic_long_t so that 64bit arches dont need 
a spinlock any more, and new percpu_lcounter would be ok for
counters that dont need s64 but a plain long (nr_files, network
counters...)

struct percpu_lcounter {
        atomic_long_t count;
#ifdef CONFIG_SMP
#ifdef CONFIG_HOTPLUG_CPU
        struct list_head list;  /* All percpu_counters are on a list */
#endif
        atomic_long_t *counters;
#endif
};

void __percpu_lcounter_add(struct percpu_lcounter *fbc, long amount, s32 batch)
{
        long count;
        atomic_long_t *pcount;

        pcount = per_cpu_ptr(fbc->counters, get_cpu());
        count = atomic_long_add_return(amount, pcount);
        if (unlikely(count >= batch || count <= -batch)) {
                atomic_long_add(count, &fbc->count);
                atomic_long_sub(count, pcount);
        }
        put_cpu();
}


long percpu_lcounter_sum(struct percpu_lcounter *fbc)
{
        long accumulator = 0, val;
        int cpu;

        for_each_online_cpu(cpu) {
                atomic_long_t *pcount = per_cpu_ptr(fbc->counters, cpu);

                val = atomic_long_xchg(pcount, 0);
                accumulator += val;
        }
        return atomic_long_add_return(accumulator, &fbc->count);
}

Then I found the following typo :

[PATCH] atomic: fix a typo in atomic_long_xchg()

atomic_long_xchg() not correctly defined for 32bit arches.

Signed-off-by: Eric Dumazet <dada1@...mosbay.com>
---
diff --git a/include/asm-generic/atomic.h b/include/asm-generic/atomic.h
index 4ec0a29..7abdaa9 100644
--- a/include/asm-generic/atomic.h
+++ b/include/asm-generic/atomic.h
@@ -251,7 +251,7 @@ static inline long atomic_long_add_unless(atomic_long_t *l, long a, long u)
 #define atomic_long_cmpxchg(l, old, new) \
 	(atomic_cmpxchg((atomic_t *)(l), (old), (new)))
 #define atomic_long_xchg(v, new) \
-	(atomic_xchg((atomic_t *)(l), (new)))
+	(atomic_xchg((atomic_t *)(v), (new)))
 
 #endif  /*  BITS_PER_LONG == 64  */
 

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