Take buffer lock while inspecting btree index pages in contrib/pageinspect.

It's not safe to examine a shared buffer without any lock.

diff --git a/contrib/pageinspect/btreefuncs.c b/contrib/pageinspect/btreefuncs.c
index dbb2158ba8da458fd3b7d1bc6e062b054c4d7cfb..bc34af9b3c7960e39321bc8903f385a75eb2d8a3 100644 (file)
--- a/contrib/pageinspect/btreefuncs.c
+++ b/contrib/pageinspect/btreefuncs.c
@@ -156,9 +156,9 @@ GetBTPageStatistics(BlockNumber blkno, Buffer buffer, BTPageStat *stat)
 }
 
 /* -----------------------------------------------
- * bt_page()
+ * bt_page_stats()
  *
- * Usage: SELECT * FROM bt_page('t1_pkey', 1);
+ * Usage: SELECT * FROM bt_page_stats('t1_pkey', 1);
  * -----------------------------------------------
  */
 Datum
@@ -204,6 +204,7 @@ bt_page_stats(PG_FUNCTION_ARGS)
    CHECK_RELATION_BLOCK_RANGE(rel, blkno);
 
    buffer = ReadBuffer(rel, blkno);
+   LockBuffer(buffer, BUFFER_LOCK_SHARE);
 
    /* keep compiler quiet */
    stat.btpo_prev = stat.btpo_next = InvalidBlockNumber;
@@ -211,6 +212,9 @@ bt_page_stats(PG_FUNCTION_ARGS)
 
    GetBTPageStatistics(blkno, buffer, &stat);
 
+   UnlockReleaseBuffer(buffer);
+   relation_close(rel, AccessShareLock);
+
    /* Build a tuple descriptor for our result type */
    if (get_call_result_type(fcinfo, NULL, &tupleDesc) != TYPEFUNC_COMPOSITE)
        elog(ERROR, "return type must be a row type");
@@ -247,10 +251,6 @@ bt_page_stats(PG_FUNCTION_ARGS)
 
    result = HeapTupleGetDatum(tuple);
 
-   ReleaseBuffer(buffer);
-
-   relation_close(rel, AccessShareLock);
-
    PG_RETURN_DATUM(result);
 }
 
@@ -322,6 +322,7 @@ bt_page_items(PG_FUNCTION_ARGS)
        CHECK_RELATION_BLOCK_RANGE(rel, blkno);
 
        buffer = ReadBuffer(rel, blkno);
+       LockBuffer(buffer, BUFFER_LOCK_SHARE);
 
        /*
         * We copy the page into local storage to avoid holding pin on the
@@ -335,7 +336,7 @@ bt_page_items(PG_FUNCTION_ARGS)
        uargs->page = palloc(BLCKSZ);
        memcpy(uargs->page, BufferGetPage(buffer), BLCKSZ);
 
-       ReleaseBuffer(buffer);
+       UnlockReleaseBuffer(buffer);
        relation_close(rel, AccessShareLock);
 
        uargs->offset = FirstOffsetNumber;
@@ -466,6 +467,8 @@ bt_metap(PG_FUNCTION_ARGS)
                 errmsg("cannot access temporary tables of other sessions")));
 
    buffer = ReadBuffer(rel, 0);
+   LockBuffer(buffer, BUFFER_LOCK_SHARE);
+
    page = BufferGetPage(buffer);
    metad = BTPageGetMeta(page);
 
@@ -492,8 +495,7 @@ bt_metap(PG_FUNCTION_ARGS)
 
    result = HeapTupleGetDatum(tuple);
 
-   ReleaseBuffer(buffer);
-
+   UnlockReleaseBuffer(buffer);
    relation_close(rel, AccessShareLock);
 
    PG_RETURN_DATUM(result);