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Commit35b039a

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Repair oversights in the mechanism used to store compiled plpgsql functions.
The original coding failed (tried to access deallocated memory) if there weretwo active call sites (fn_extra pointers) for the same function and thefunction definition was updated. Also, if an update of a recursive functionwas detected upon nested entry to the function, the existing compiled versionwas summarily deallocated, resulting in crash upon return to the outerinstance. Problem observed while studying a bug report from SergiyVyshnevetskiy.Bug does not exist before 8.1 since older versions just leaked the memory ofobsoleted compiled functions, rather than trying to reclaim it.
1 parent33d78c9 commit35b039a

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3 files changed

+115
-31
lines changed

3 files changed

+115
-31
lines changed

‎src/pl/plpgsql/src/pl_comp.c‎

Lines changed: 88 additions & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_comp.c,v 1.109 2007/01/05 22:20:02 momjian Exp $
11+
* $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_comp.c,v 1.110 2007/01/30 22:05:12 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -93,6 +93,7 @@ static const ExceptionLabelMap exception_label_map[] = {
9393
*/
9494
staticPLpgSQL_function*do_compile(FunctionCallInfofcinfo,
9595
HeapTupleprocTup,
96+
PLpgSQL_function*function,
9697
PLpgSQL_func_hashkey*hashkey,
9798
boolforValidator);
9899
staticPLpgSQL_row*build_row_from_class(OidclassOid);
@@ -130,6 +131,7 @@ plpgsql_compile(FunctionCallInfo fcinfo, bool forValidator)
130131
Form_pg_procprocStruct;
131132
PLpgSQL_function*function;
132133
PLpgSQL_func_hashkeyhashkey;
134+
boolfunction_valid= false;
133135
boolhashkey_valid= false;
134136

135137
/*
@@ -148,6 +150,7 @@ plpgsql_compile(FunctionCallInfo fcinfo, bool forValidator)
148150
*/
149151
function= (PLpgSQL_function*)fcinfo->flinfo->fn_extra;
150152

153+
recheck:
151154
if (!function)
152155
{
153156
/* Compute hashkey using function signature and actual arg types */
@@ -161,19 +164,43 @@ plpgsql_compile(FunctionCallInfo fcinfo, bool forValidator)
161164
if (function)
162165
{
163166
/* We have a compiled function, but is it still valid? */
164-
if (!(function->fn_xmin==HeapTupleHeaderGetXmin(procTup->t_data)&&
165-
function->fn_cmin==HeapTupleHeaderGetCmin(procTup->t_data)))
167+
if (function->fn_xmin==HeapTupleHeaderGetXmin(procTup->t_data)&&
168+
function->fn_cmin==HeapTupleHeaderGetCmin(procTup->t_data))
169+
function_valid= true;
170+
else
166171
{
167-
/* Nope, drop the function and associated storage */
172+
/*
173+
* Nope, so remove it from hashtable and try to drop associated
174+
* storage (if not done already).
175+
*/
168176
delete_function(function);
169-
function=NULL;
177+
/*
178+
* If the function isn't in active use then we can overwrite the
179+
* func struct with new data, allowing any other existing fn_extra
180+
* pointers to make use of the new definition on their next use.
181+
* If it is in use then just leave it alone and make a new one.
182+
* (The active invocations will run to completion using the
183+
* previous definition, and then the cache entry will just be
184+
* leaked; doesn't seem worth adding code to clean it up, given
185+
* what a corner case this is.)
186+
*
187+
* If we found the function struct via fn_extra then it's possible
188+
* a replacement has already been made, so go back and recheck
189+
* the hashtable.
190+
*/
191+
if (function->use_count!=0)
192+
{
193+
function=NULL;
194+
if (!hashkey_valid)
195+
gotorecheck;
196+
}
170197
}
171198
}
172199

173200
/*
174201
* If the function wasn't found or was out-of-date, we have to compile it
175202
*/
176-
if (!function)
203+
if (!function_valid)
177204
{
178205
/*
179206
* Calculate hashkey if we didn't already; we'll need it to store the
@@ -186,7 +213,8 @@ plpgsql_compile(FunctionCallInfo fcinfo, bool forValidator)
186213
/*
187214
* Do the hard part.
188215
*/
189-
function=do_compile(fcinfo,procTup,&hashkey,forValidator);
216+
function=do_compile(fcinfo,procTup,function,
217+
&hashkey,forValidator);
190218
}
191219

192220
ReleaseSysCache(procTup);
@@ -205,6 +233,9 @@ plpgsql_compile(FunctionCallInfo fcinfo, bool forValidator)
205233
/*
206234
* This is the slow part of plpgsql_compile().
207235
*
236+
* The passed-in "function" pointer is either NULL or an already-allocated
237+
* function struct to overwrite.
238+
*
208239
* While compiling a function, the CurrentMemoryContext is the
209240
* per-function memory context of the function we are compiling. That
210241
* means a palloc() will allocate storage with the same lifetime as
@@ -217,16 +248,19 @@ plpgsql_compile(FunctionCallInfo fcinfo, bool forValidator)
217248
* switch into a short-term context before calling into the
218249
* backend. An appropriate context for performing short-term
219250
* allocations is the compile_tmp_cxt.
251+
*
252+
* NB: this code is not re-entrant. We assume that nothing we do here could
253+
* result in the invocation of another plpgsql function.
220254
*/
221255
staticPLpgSQL_function*
222256
do_compile(FunctionCallInfofcinfo,
223257
HeapTupleprocTup,
258+
PLpgSQL_function*function,
224259
PLpgSQL_func_hashkey*hashkey,
225260
boolforValidator)
226261
{
227262
Form_pg_procprocStruct= (Form_pg_proc)GETSTRUCT(procTup);
228263
intfunctype=CALLED_AS_TRIGGER(fcinfo) ?T_TRIGGER :T_FUNCTION;
229-
PLpgSQL_function*function;
230264
Datumprosrcdatum;
231265
boolisnull;
232266
char*proc_source;
@@ -292,18 +326,31 @@ do_compile(FunctionCallInfo fcinfo,
292326
plpgsql_check_syntax=forValidator;
293327

294328
/*
295-
* Create the new function node. We allocate the function and all of its
296-
* compile-time storage (e.g. parse tree) in its own memory context. This
297-
* allows us to reclaim the function's storage cleanly.
329+
* Create the new function struct, if not done already. The function
330+
* structs are never thrown away, so keep them in TopMemoryContext.
331+
*/
332+
if (function==NULL)
333+
{
334+
function= (PLpgSQL_function*)
335+
MemoryContextAllocZero(TopMemoryContext,sizeof(PLpgSQL_function));
336+
}
337+
else
338+
{
339+
/* re-using a previously existing struct, so clear it out */
340+
memset(function,0,sizeof(PLpgSQL_function));
341+
}
342+
plpgsql_curr_compile=function;
343+
344+
/*
345+
* All the rest of the compile-time storage (e.g. parse tree) is kept in
346+
* its own memory context, so it can be reclaimed easily.
298347
*/
299348
func_cxt=AllocSetContextCreate(TopMemoryContext,
300349
"PL/PgSQL function context",
301350
ALLOCSET_DEFAULT_MINSIZE,
302351
ALLOCSET_DEFAULT_INITSIZE,
303352
ALLOCSET_DEFAULT_MAXSIZE);
304353
compile_tmp_cxt=MemoryContextSwitchTo(func_cxt);
305-
function=palloc0(sizeof(*function));
306-
plpgsql_curr_compile=function;
307354

308355
function->fn_name=pstrdup(NameStr(procStruct->proname));
309356
function->fn_oid=fcinfo->flinfo->fn_oid;
@@ -1990,19 +2037,32 @@ plpgsql_resolve_polymorphic_argtypes(int numargs,
19902037
}
19912038
}
19922039

2040+
/*
2041+
* delete_function - clean up as much as possible of a stale function cache
2042+
*
2043+
* We can't release the PLpgSQL_function struct itself, because of the
2044+
* possibility that there are fn_extra pointers to it. We can release
2045+
* the subsidiary storage, but only if there are no active evaluations
2046+
* in progress. Otherwise we'll just leak that storage. Since the
2047+
* case would only occur if a pg_proc update is detected during a nested
2048+
* recursive call on the function, a leak seems acceptable.
2049+
*
2050+
* Note that this can be called more than once if there are multiple fn_extra
2051+
* pointers to the same function cache. Hence be careful not to do things
2052+
* twice.
2053+
*/
19932054
staticvoid
19942055
delete_function(PLpgSQL_function*func)
19952056
{
1996-
/* remove function from hash table */
2057+
/* remove function from hash table(might be done already)*/
19972058
plpgsql_HashTableDelete(func);
19982059

1999-
/* release the function's storage */
2000-
MemoryContextDelete(func->fn_cxt);
2001-
2002-
/*
2003-
* Caller should be sure not to use passed-in pointer, as it now points to
2004-
* pfree'd storage
2005-
*/
2060+
/* release the function's storage if safe and not done already */
2061+
if (func->use_count==0&&func->fn_cxt)
2062+
{
2063+
MemoryContextDelete(func->fn_cxt);
2064+
func->fn_cxt=NULL;
2065+
}
20062066
}
20072067

20082068
/* exported so we can call it from plpgsql_init() */
@@ -2063,10 +2123,17 @@ plpgsql_HashTableDelete(PLpgSQL_function *function)
20632123
{
20642124
plpgsql_HashEnt*hentry;
20652125

2126+
/* do nothing if not in table */
2127+
if (function->fn_hashkey==NULL)
2128+
return;
2129+
20662130
hentry= (plpgsql_HashEnt*)hash_search(plpgsql_HashTable,
20672131
(void*)function->fn_hashkey,
20682132
HASH_REMOVE,
20692133
NULL);
20702134
if (hentry==NULL)
20712135
elog(WARNING,"trying to delete function that does not exist");
2136+
2137+
/* remove back link, which no longer points to allocated storage */
2138+
function->fn_hashkey=NULL;
20722139
}

‎src/pl/plpgsql/src/pl_handler.c‎

Lines changed: 24 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_handler.c,v 1.35 2007/01/28 16:15:49 tgl Exp $
11+
* $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_handler.c,v 1.36 2007/01/30 22:05:13 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -79,15 +79,30 @@ plpgsql_call_handler(PG_FUNCTION_ARGS)
7979
/* Find or compile the function */
8080
func=plpgsql_compile(fcinfo, false);
8181

82-
/*
83-
* Determine if called as function or trigger and call appropriate
84-
* subhandler
85-
*/
86-
if (CALLED_AS_TRIGGER(fcinfo))
87-
retval=PointerGetDatum(plpgsql_exec_trigger(func,
82+
/* Mark the function as busy, so it can't be deleted from under us */
83+
func->use_count++;
84+
85+
PG_TRY();
86+
{
87+
/*
88+
* Determine if called as function or trigger and call appropriate
89+
* subhandler
90+
*/
91+
if (CALLED_AS_TRIGGER(fcinfo))
92+
retval=PointerGetDatum(plpgsql_exec_trigger(func,
8893
(TriggerData*)fcinfo->context));
89-
else
90-
retval=plpgsql_exec_function(func,fcinfo);
94+
else
95+
retval=plpgsql_exec_function(func,fcinfo);
96+
}
97+
PG_CATCH();
98+
{
99+
/* Decrement use-count and propagate error */
100+
func->use_count--;
101+
PG_RE_THROW();
102+
}
103+
PG_END_TRY();
104+
105+
func->use_count--;
91106

92107
/*
93108
* Disconnect from SPI manager

‎src/pl/plpgsql/src/plpgsql.h‎

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/pl/plpgsql/src/plpgsql.h,v 1.83 2007/01/28 16:15:49 tgl Exp $
11+
* $PostgreSQL: pgsql/src/pl/plpgsql/src/plpgsql.h,v 1.84 2007/01/30 22:05:13 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -580,6 +580,8 @@ typedef struct PLpgSQL_function
580580
intndatums;
581581
PLpgSQL_datum**datums;
582582
PLpgSQL_stmt_block*action;
583+
584+
unsigned longuse_count;
583585
}PLpgSQL_function;
584586

585587

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