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Commita8b330f

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Fix dsa.c with different resource owners.
The comments in dsa.c suggested that areas were owned by resourceowners, but it was not in fact tracked explicitly. The DSM attachmentsheld by the dsa were owned by resource owners, but not the areaitself. That led to confusion if you used one resource owner toattach or create the area, but then switched to a different resourceowner before allocating or even just accessing the allocations in thearea with dsa_get_address(). The additional DSM segments associatedwith the area would get owned by a different resource owner than theinitial segment. To fix, add an explicit 'resowner' field todsa_area. It replaces the 'mapping_pinned' flag; resowner == NULL nowindicates that the mapping is pinned.This is arguably a bug fix, but I'm not backpatching because itdoesn't seem to be a live bug in the back branches. In 'master', it isa bug because commitb8bff07 made ResourceOwners more strict sothat you are no longer allowed to remember new resources in aResourceOwner after you have started to release it. Merely accessing adsa pointer might need to attach a new DSM segment, and before thiscommit it was temporarily remembered in the current owner for a verybrief period even if the DSA was pinned. And that could happen inAtEOXact_PgStat(), which is called after the owner is already released.Reported-by: Alexander LakhinReviewed-by: Alexander Lakhin, Thomas Munro, Andres FreundDiscussion:https://www.postgresql.org/message-id/11b70743-c5f3-3910-8e5b-dd6c115ff829%40gmail.com
1 parentf26c236 commita8b330f

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1 file changed

+25
-13
lines changed
  • src/backend/utils/mmgr

1 file changed

+25
-13
lines changed

‎src/backend/utils/mmgr/dsa.c

Lines changed: 25 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -59,6 +59,7 @@
5959
#include"utils/dsa.h"
6060
#include"utils/freepage.h"
6161
#include"utils/memutils.h"
62+
#include"utils/resowner.h"
6263

6364
/*
6465
* The size of the initial DSM segment that backs a dsa_area created by
@@ -368,8 +369,13 @@ struct dsa_area
368369
/* Pointer to the control object in shared memory. */
369370
dsa_area_control*control;
370371

371-
/* Has the mapping been pinned? */
372-
boolmapping_pinned;
372+
/*
373+
* All the mappings are owned by this. The dsa_area itself is not
374+
* directly tracked by the ResourceOwner, but the effect is the same. NULL
375+
* if the attachment has session lifespan, i.e if dsa_pin_mapping() has
376+
* been called.
377+
*/
378+
ResourceOwnerresowner;
373379

374380
/*
375381
* This backend's array of segment maps, ordered by segment index
@@ -645,12 +651,14 @@ dsa_pin_mapping(dsa_area *area)
645651
{
646652
inti;
647653

648-
Assert(!area->mapping_pinned);
649-
area->mapping_pinned= true;
654+
if (area->resowner!=NULL)
655+
{
656+
area->resowner=NULL;
650657

651-
for (i=0;i <=area->high_segment_index;++i)
652-
if (area->segment_maps[i].segment!=NULL)
653-
dsm_pin_mapping(area->segment_maps[i].segment);
658+
for (i=0;i <=area->high_segment_index;++i)
659+
if (area->segment_maps[i].segment!=NULL)
660+
dsm_pin_mapping(area->segment_maps[i].segment);
661+
}
654662
}
655663

656664
/*
@@ -1264,7 +1272,7 @@ create_internal(void *place, size_t size,
12641272
*/
12651273
area=palloc(sizeof(dsa_area));
12661274
area->control=control;
1267-
area->mapping_pinned=false;
1275+
area->resowner=CurrentResourceOwner;
12681276
memset(area->segment_maps,0,sizeof(dsa_segment_map)*DSA_MAX_SEGMENTS);
12691277
area->high_segment_index=0;
12701278
area->freed_segment_counter=0;
@@ -1320,7 +1328,7 @@ attach_internal(void *place, dsm_segment *segment, dsa_handle handle)
13201328
/* Build the backend-local area object. */
13211329
area=palloc(sizeof(dsa_area));
13221330
area->control=control;
1323-
area->mapping_pinned=false;
1331+
area->resowner=CurrentResourceOwner;
13241332
memset(&area->segment_maps[0],0,
13251333
sizeof(dsa_segment_map)*DSA_MAX_SEGMENTS);
13261334
area->high_segment_index=0;
@@ -1743,6 +1751,7 @@ get_segment_by_index(dsa_area *area, dsa_segment_index index)
17431751
dsm_handlehandle;
17441752
dsm_segment*segment;
17451753
dsa_segment_map*segment_map;
1754+
ResourceOwneroldowner;
17461755

17471756
/*
17481757
* If we are reached by dsa_free or dsa_get_address, there must be at
@@ -1761,11 +1770,12 @@ get_segment_by_index(dsa_area *area, dsa_segment_index index)
17611770
elog(ERROR,
17621771
"dsa_area could not attach to a segment that has been freed");
17631772

1773+
oldowner=CurrentResourceOwner;
1774+
CurrentResourceOwner=area->resowner;
17641775
segment=dsm_attach(handle);
1776+
CurrentResourceOwner=oldowner;
17651777
if (segment==NULL)
17661778
elog(ERROR,"dsa_area could not attach to segment");
1767-
if (area->mapping_pinned)
1768-
dsm_pin_mapping(segment);
17691779
segment_map=&area->segment_maps[index];
17701780
segment_map->segment=segment;
17711781
segment_map->mapped_address=dsm_segment_address(segment);
@@ -2067,6 +2077,7 @@ make_new_segment(dsa_area *area, size_t requested_pages)
20672077
size_tusable_pages;
20682078
dsa_segment_map*segment_map;
20692079
dsm_segment*segment;
2080+
ResourceOwneroldowner;
20702081

20712082
Assert(LWLockHeldByMe(DSA_AREA_LOCK(area)));
20722083

@@ -2151,12 +2162,13 @@ make_new_segment(dsa_area *area, size_t requested_pages)
21512162
}
21522163

21532164
/* Create the segment. */
2165+
oldowner=CurrentResourceOwner;
2166+
CurrentResourceOwner=area->resowner;
21542167
segment=dsm_create(total_size,0);
2168+
CurrentResourceOwner=oldowner;
21552169
if (segment==NULL)
21562170
returnNULL;
21572171
dsm_pin_segment(segment);
2158-
if (area->mapping_pinned)
2159-
dsm_pin_mapping(segment);
21602172

21612173
/* Store the handle in shared memory to be found by index. */
21622174
area->control->segment_handles[new_index]=

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