foreach() and list_delete() don't mix.

Fix crash when releasing duplicate entries in the encoding conversion cache
list, caused by releasing the current entry of the list being chased by
foreach().  We have a standard idiom for handling such cases, but this
loop wasn't using it.

This got broken in my recent rewrite of GUC assign hooks.  Not sure how
I missed this when testing the modified code, but I did.  Per report from
Peter.

diff --git a/src/backend/utils/mb/mbutils.c b/src/backend/utils/mb/mbutils.c
index 234bb0cf6e839ec3ee8f270e41a9ff9f2181a612..3cb7ce3269d384474ea2717cddf25660fa89ff77 100644 (file)
--- a/src/backend/utils/mb/mbutils.c
+++ b/src/backend/utils/mb/mbutils.c
@@ -189,6 +189,8 @@ SetClientEncoding(int encoding)
        int                     current_server_encoding;
        bool            found;
        ListCell   *lc;
+       ListCell   *prev;
+       ListCell   *next;
 
        if (!PG_VALID_FE_ENCODING(encoding))
                return -1;
@@ -222,10 +224,13 @@ SetClientEncoding(int encoding)
         * leak memory.
         */
        found = false;
-       foreach(lc, ConvProcList)
+       prev = NULL;
+       for (lc = list_head(ConvProcList); lc; lc = next)
        {
                ConvProcInfo *convinfo = (ConvProcInfo *) lfirst(lc);
 
+               next = lnext(lc);
+
                if (convinfo->s_encoding == current_server_encoding &&
                        convinfo->c_encoding == encoding)
                {
@@ -240,10 +245,13 @@ SetClientEncoding(int encoding)
                        else
                        {
                                /* Duplicate entry, release it */
-                               ConvProcList = list_delete_ptr(ConvProcList, convinfo);
+                               ConvProcList = list_delete_cell(ConvProcList, lc, prev);
                                pfree(convinfo);
+                               continue;               /* prev mustn't advance */
                        }
                }
+
+               prev = lc;
        }
 
        if (found)