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Fix longstanding race condition in plancache.c.

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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.
This commit is contained in:
Tom Lane 2013-04-20 16:59:27 -04:00
parent e3a7675e67
commit c37ec840cf
1 changed files with 42 additions and 9 deletions
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43
src/backend/utils/cache/plancache.c vendored
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@ -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);
@ -384,8 +393,11 @@ 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.
*/
if (!IsTransactionStmtPlan(plansource))
plansource->search_path = GetOverrideSearchPath(source_context);
plansource->is_complete = 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;
@ -859,6 +873,7 @@ BuildCachedPlan(CachedPlanSource *plansource, List *qlist,
* compared to parse analysis + planning, I'm not going to contort the
* code enough to avoid that.
*/
if (plansource->search_path)
PushOverrideSearchPath(plansource->search_path);
/*
@ -894,6 +909,7 @@ BuildCachedPlan(CachedPlanSource *plansource, List *qlist,
PopActiveSnapshot();
/* Now we can restore current search path */
if (plansource->search_path)
PopOverrideSearchPath();
/*
@ -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)
@ -1267,6 +1286,7 @@ CopyCachedPlan(CachedPlanSource *plansource)
newsource->resultDesc = CreateTupleDescCopy(plansource->resultDesc);
else
newsource->resultDesc = NULL;
if (plansource->search_path)
newsource->search_path = CopyOverrideSearchPath(plansource->search_path);
newsource->context = 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