Bdb(4.4 and 4.7) goes to infinite ride when used from 8 core box.

Question

We use bdb-4.7(This bug is reproducible with bdb-4.4 too) with subversion 1.5.
When we run 'svn log -g' in one window and 'commit in another window' we could see 'infinite' loop inside bdb code.
I could trace the infinite loop to the following code.
#define     SH_LIST_NEXT(elm, field, type)                         \
     ((elm)->field.sle_next == -1 ? NULL :                    \
     ((struct type *)(((u_int8_t *)(elm)) + (elm)->field.sle_next)))
In our execution context (elm)->field.sle_next happened to be 0.
And hence infinite loop.
I am not sure (elm)->field.sle_next need to be guarded at the population stage itself or at SH_LIST_NEXT.
This bug happens only with 8-core box with bdb data being from NFS.
I believe the following patch should fix this, but I am concerned about applying this patch to bdb code that used to work fine for so many years.
--- dbinc/shqueue.h     2008-08-28 19:26:54.000000000 +0530
+++ dbinc/shqueue.h     2008-08-28 19:28:28.000000000 +0530
@@ -70,7 +70,7 @@
     ((struct type *)(((u_int8_t *)(elm)) + (elm)->field.sle_next))
#define     SH_LIST_NEXT(elm, field, type)                         \
-     ((elm)->field.sle_next == -1 ? NULL :                    \
+     (((elm)->field.sle_next == -1) || ((elm)->field.sle_next == 0) ? NULL:\
     ((struct type *)(((u_int8_t *)(elm)) + (elm)->field.sle_next)))
I would like to know what Oracle thinks about this.
With regards
Kamesh Jayachandran

Answer 1

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