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revert "percpu_counter: new function percpu_counter_sum_and_set"

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Revert

    commit e8ced39d5e
    Author: Mingming Cao <cmm@us.ibm.com>
    Date:   Fri Jul 11 19:27:31 2008 -0400

        percpu_counter: new function percpu_counter_sum_and_set

As described in

	revert "percpu counter: clean up percpu_counter_sum_and_set()"

the new percpu_counter_sum_and_set() is racy against updates to the
cpu-local accumulators on other CPUs.  Revert that change.

This means that ext4 will be slow again.  But correct.

Reported-by: Eric Dumazet <dada1@cosmosbay.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mingming Cao <cmm@us.ibm.com>
Cc: <linux-ext4@vger.kernel.org>
Cc: <stable@kernel.org>		[2.6.27.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrew Morton
2008-12-09 13:14:14 -08:00
committed by Linus Torvalds
parent 71c5576fbd
commit 02d2116887
3 changed files with 6 additions and 17 deletions
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7
lib/percpu_counter.c
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@@ -52,7 +52,7 @@ EXPORT_SYMBOL(__percpu_counter_add);
* Add up all the per-cpu counts, return the result. This is a more accurate
* but much slower version of percpu_counter_read_positive()
*/
s64 __percpu_counter_sum(struct percpu_counter *fbc, int set)
s64 __percpu_counter_sum(struct percpu_counter *fbc)
{
s64 ret;
int cpu;
@@ -62,12 +62,7 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc, int set)
for_each_online_cpu(cpu) {
s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
ret += *pcount;
if (set)
*pcount = 0;
}
if (set)
fbc->count = ret;
spin_unlock(&fbc->lock);
return ret;
}