postgres.git / summary / log / commit / refs
commit c37ec840cfe80e8fde05bc87417ced2765ab17dd
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat Apr 20 20:59:27 2013 +0000
First released in: 9.3.0, 8.4.18, 9.0.14, 9.1.10, 9.2.5
Fix longstanding race condition in plancache.c.
When creating or manipulating a cached plan for a transaction control
command (particularly ROLLBACK), we must not perform any catalog accesses,
since we might be in an aborted transaction. However, plancache.c busily
saved or examined the search_path for every cached plan. If we were
unlucky enough to do this at a moment where the path's expansion into
schema OIDs wasn't already cached, we'd do some catalog accesses; and with
some more bad luck such as an ill-timed signal arrival, that could lead to
crashes or Assert failures, as exhibited in bug #8095 from Nachiket Vaidya.
Fortunately, there's no real need to consider the search path for such
commands, so we can just skip the relevant steps when the subject statement
is a TransactionStmt. This is somewhat related to bug #5269, though the
failure happens during initial cached-plan creation rather than
revalidation.
This bug has been there since the plan cache was invented, so back-patch
to all supported branches.
src/backend/utils/cache/plancache.c | 51 ++++++++++++++++++++++++++++++-------
1 file changed, 42 insertions(+), 9 deletions(-)
diff --git a/src/backend/utils/cache/plancache.c b/src/backend/utils/cache/plancache.c
index c46264f1c61..c2ad20c25c3 100644
--- a/src/backend/utils/cache/plancache.c
+++ b/src/backend/utils/cache/plancache.c
@@ -65,6 +65,14 @@
#include "utils/syscache.h"
+/*
+ * We must skip "overhead" operations that involve database access when the
+ * cached plan's subject statement is a transaction control command.
+ */
+#define IsTransactionStmtPlan(plansource) \
+ ((plansource)->raw_parse_tree && \
+ IsA((plansource)->raw_parse_tree, TransactionStmt))
+
/*
* This is the head of the backend's list of "saved" CachedPlanSources (i.e.,
* those that are in long-lived storage and are examined for sinval events).
@@ -352,9 +360,10 @@ CompleteCachedPlan(CachedPlanSource *plansource,
/*
* Use the planner machinery to extract dependencies. Data is saved in
* query_context. (We assume that not a lot of extra cruft is created by
- * this call.) We can skip this for one-shot plans.
+ * this call.) We can skip this for one-shot plans, and transaction
+ * control commands have no such dependencies anyway.
*/
- if (!plansource->is_oneshot)
+ if (!plansource->is_oneshot && !IsTransactionStmtPlan(plansource))
extract_query_dependencies((Node *) querytree_list,
&plansource->relationOids,
&plansource->invalItems);
@@ -384,9 +393,12 @@ CompleteCachedPlan(CachedPlanSource *plansource,
/*
* Fetch current search_path into dedicated context, but do any
- * recalculation work required in caller's context.
+ * recalculation work required in caller's context. We *must* skip this
+ * for transaction control commands, because this could result in catalog
+ * accesses.
*/
- plansource->search_path = GetOverrideSearchPath(source_context);
+ if (!IsTransactionStmtPlan(plansource))
+ plansource->search_path = GetOverrideSearchPath(source_context);
plansource->is_complete = true;
plansource->is_valid = true;
@@ -537,9 +549,11 @@ RevalidateCachedQuery(CachedPlanSource *plansource)
/*
* For one-shot plans, we do not support revalidation checking; it's
* assumed the query is parsed, planned, and executed in one transaction,
- * so that no lock re-acquisition is necessary.
+ * so that no lock re-acquisition is necessary. Also, there is never
+ * any need to revalidate plans for transaction control commands (and
+ * we mustn't risk any catalog accesses when handling those).
*/
- if (plansource->is_oneshot)
+ if (plansource->is_oneshot || IsTransactionStmtPlan(plansource))
{
Assert(plansource->is_valid);
return NIL;
@@ -859,7 +873,8 @@ BuildCachedPlan(CachedPlanSource *plansource, List *qlist,
* compared to parse analysis + planning, I'm not going to contort the
* code enough to avoid that.
*/
- PushOverrideSearchPath(plansource->search_path);
+ if (plansource->search_path)
+ PushOverrideSearchPath(plansource->search_path);
/*
* If a snapshot is already set (the normal case), we can just use that
@@ -894,7 +909,8 @@ BuildCachedPlan(CachedPlanSource *plansource, List *qlist,
PopActiveSnapshot();
/* Now we can restore current search path */
- PopOverrideSearchPath();
+ if (plansource->search_path)
+ PopOverrideSearchPath();
/*
* Normally we make a dedicated memory context for the CachedPlan and its
@@ -965,6 +981,9 @@ choose_custom_plan(CachedPlanSource *plansource, ParamListInfo boundParams)
/* Otherwise, never any point in a custom plan if there's no parameters */
if (boundParams == NULL)
return false;
+ /* ... nor for transaction control statements */
+ if (IsTransactionStmtPlan(plansource))
+ return false;
/* See if caller wants to force the decision */
if (plansource->cursor_options & CURSOR_OPT_GENERIC_PLAN)
@@ -1267,7 +1286,8 @@ CopyCachedPlan(CachedPlanSource *plansource)
newsource->resultDesc = CreateTupleDescCopy(plansource->resultDesc);
else
newsource->resultDesc = NULL;
- newsource->search_path = CopyOverrideSearchPath(plansource->search_path);
+ if (plansource->search_path)
+ newsource->search_path = CopyOverrideSearchPath(plansource->search_path);
newsource->context = source_context;
querytree_context = AllocSetContextCreate(source_context,
@@ -1619,6 +1639,10 @@ PlanCacheRelCallback(Datum arg, Oid relid)
if (!plansource->is_valid)
continue;
+ /* Never invalidate transaction control commands */
+ if (IsTransactionStmtPlan(plansource))
+ continue;
+
/*
* Check the dependency list for the rewritten querytree.
*/
@@ -1683,6 +1707,10 @@ PlanCacheFuncCallback(Datum arg, int cacheid, uint32 hashvalue)
if (!plansource->is_valid)
continue;
+ /* Never invalidate transaction control commands */
+ if (IsTransactionStmtPlan(plansource))
+ continue;
+
/*
* Check the dependency list for the rewritten querytree.
*/
@@ -1772,6 +1800,11 @@ ResetPlanCache(void)
* We *must not* mark transaction control statements as invalid,
* particularly not ROLLBACK, because they may need to be executed in
* aborted transactions when we can't revalidate them (cf bug #5269).
+ */
+ if (IsTransactionStmtPlan(plansource))
+ continue;
+
+ /*
* In general there is no point in invalidating utility statements
* since they have no plans anyway. So invalidate it only if it
* contains at least one non-utility statement, or contains a utility
[parent: e3a7675e6718]