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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.
This commit is contained in:
Tom Lane 2013-04-20 16:59:21 -04:00
parent 61b962345d
commit ac63dca607
1 changed files with 44 additions and 14 deletions
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58
src/backend/utils/cache/plancache.c vendored
View File

@ -68,6 +68,14 @@
#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).
@ -352,23 +360,27 @@ CompleteCachedPlan(CachedPlanSource *plansource,
plansource->query_context = querytree_context;
plansource->query_list = querytree_list;
/*
* 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.
*/
if (!plansource->is_oneshot)
if (!plansource->is_oneshot && !IsTransactionStmtPlan(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, and
* transaction control commands have no such dependencies anyway.
*/
extract_query_dependencies((Node *) querytree_list,
&plansource->relationOids,
&plansource->invalItems);
/*
* Also save the current search_path in the query_context. (This should
* not generate much extra cruft either, since almost certainly the path
* is already valid.) Again, don't really need it for one-shot plans.
*/
if (!plansource->is_oneshot)
/*
* Also save the current search_path in the query_context. (This
* should not generate much extra cruft either, since almost certainly
* the path is already valid.) Again, we don't really need this for
* one-shot plans; and we *must* skip this for transaction control
* commands, because this could result in catalog accesses.
*/
plansource->search_path = GetOverrideSearchPath(querytree_context);
}
/*
* Save the final parameter types (or other parameter specification data)
@ -542,9 +554,11 @@ 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;
@ -967,6 +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)
@ -1622,6 +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.
*/
@ -1686,6 +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.
*/
@ -1775,6 +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