Fix wrap-around in memusage.

2 files changed, 10 insertions, 4 deletions

diff --git a/ChangeLog b/ChangeLog
index 25bb325..99088df 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2009-10-29  Andreas Schwab  <schwab@redhat.com>
+
+	* malloc/memusage.c (update_data): Fix index wraparound handling
+	so that buffer_cnt is actually reset.
+
 2009-10-29  Ulrich Drepper  <drepper@redhat.com>
 
 	[BZ #10784]
diff --git a/malloc/memusage.c b/malloc/memusage.c
index fcd58dc..382261c 100644
--- a/malloc/memusage.c
+++ b/malloc/memusage.c
@@ -163,15 +163,16 @@ update_data (struct header *result, size_t len, size_t old_len)
   if (fd != -1)
     {
       uatomic32_t idx = catomic_exchange_and_add (&buffer_cnt, 1);
-      if (idx >= 2 * buffer_size)
+      if (idx + 1 >= 2 * buffer_size)
 	{
 	  /* We try to reset the counter to the correct range.  If
 	     this fails because of another thread increasing the
 	     counter it does not matter since that thread will take
 	     care of the correction.  */
-	  uatomic32_t reset = idx % (2 * buffer_size);
-	  catomic_compare_and_exchange_val_acq (&buffer_cnt, reset, idx);
-	  idx = reset;
+	  uatomic32_t reset = (idx + 1) % (2 * buffer_size);
+	  catomic_compare_and_exchange_val_acq (&buffer_cnt, reset, idx + 1);
+	  if (idx >= 2 * buffer_size)
+	    idx = reset - 1;
 	}
       assert (idx < 2 * DEFAULT_BUFFER_SIZE);