Re: [PATCH] percpu: preemptless __per_cpu_counter_add

[Christoph Lameter <cl@linux.com>]

Suggested fixup. Return from slowpath and update percpu variable under
spinlock.

Signed-off-by: Christoph Lameter <cl@linux.com>

---
 lib/percpu_counter.c |    8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

Index: linux-2.6/lib/percpu_counter.c
===================================================================
--- linux-2.6.orig/lib/percpu_counter.c	2011-04-13 17:20:41.000000000 -0500
+++ linux-2.6/lib/percpu_counter.c	2011-04-13 17:21:33.000000000 -0500
@@ -82,13 +82,9 @@ void __percpu_counter_add(struct percpu_
 			spin_lock(&fbc->lock);
 			count = __this_cpu_read(*fbc->counters);
 			fbc->count += count + amount;
+			__this_cpu_write(*fbc->counters, 0);
 			spin_unlock(&fbc->lock);
-			/*
-			 * If cmpxchg fails then we need to subtract the amount that
-			 * we found in the percpu value.
-			 */
-			amount = -count;
-			new = 0;
+			return;
 		}

 	} while (this_cpu_cmpxchg(*fbc->counters, count, new) != count);

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