[postgis-tickets] [PostGIS] #4691: Segfault when creating an index on geography(Point, 4326) column that contains empty points

[PostGIS]

#4691: Segfault when creating an index on geography(Point, 4326) column that
contains empty points
----------------------+---------------------------
  Reporter:  aktiur   |      Owner:  Algunenano
      Type:  defect   |     Status:  new
  Priority:  blocker  |  Milestone:  PostGIS 2.5.5
 Component:  postgis  |    Version:  2.5.x
Resolution:           |   Keywords:
----------------------+---------------------------

Comment (by Algunenano):

 Looking at Postgresql source code it appears that GIST uses random() in
 some cases to decide in which bucket to insert a tupe (when several of
 them are equally good) so finding a use minimal test case is going to be
 extremely hard.

 I'm going to retest the patch for a while to confirm I don't see any crash
 / invalid reads and push it that way.

 BTW, under valgrind it looks like this:
 {{{
  2020-07-29 18:21:34.532 CEST [205377] [raul @ postgis_crash] LOG:
 statement: CREATE INDEX crash_test_index ON crash_test USING gist (point);
  Invalid read of size 8
  at 0x6946AB: pfree (mcxt.c:1035)
  by 0x8525833: gserialized_gist_picksplit (gserialized_gist_nd.c:0)
  by 0x66B188: FunctionCall2Coll (fmgr.c:1162)
  by 0x211D27: gistUserPicksplit (gistsplit.c:433)
  by 0x2113F9: gistSplitByKey (gistsplit.c:697)
  by 0x208BE8: gistSplit (gist.c:1451)
  by 0x2081E0: gistplacetopage (gist.c:299)
  by 0x207DFA: gistinserttuples (gist.c:1269)
  by 0x207DFA: gistinserttuple (gist.c:1222)
  by 0x207DFA: gistdoinsert (gist.c:876)
  by 0x212E84: gistBuildCallback (gistbuild.c:489)
  by 0x22DCBA: heapam_index_build_range_scan (heapam_handler.c:1664)
  by 0x212BB4: table_index_build_scan (tableam.h:1522)
  by 0x212BB4: gistbuild (gistbuild.c:196)
  by 0x29BF4D: index_build (index.c:2912)
  Address 0x4028002200000008 is not stack'd, malloc'd or (recently) free'd


  Process terminating with default action of signal 11 (SIGSEGV): dumping
 core
  General Protection Fault
  at 0x6946AB: pfree (mcxt.c:1035)
  by 0x8525833: gserialized_gist_picksplit (gserialized_gist_nd.c:0)
  by 0x66B188: FunctionCall2Coll (fmgr.c:1162)
  by 0x211D27: gistUserPicksplit (gistsplit.c:433)
  by 0x2113F9: gistSplitByKey (gistsplit.c:697)
  by 0x208BE8: gistSplit (gist.c:1451)
  by 0x2081E0: gistplacetopage (gist.c:299)
  by 0x207DFA: gistinserttuples (gist.c:1269)
  by 0x207DFA: gistinserttuple (gist.c:1222)
  by 0x207DFA: gistdoinsert (gist.c:876)
  by 0x212E84: gistBuildCallback (gistbuild.c:489)
  by 0x22DCBA: heapam_index_build_range_scan (heapam_handler.c:1664)
  by 0x212BB4: table_index_build_scan (tableam.h:1522)
  by 0x212BB4: gistbuild (gistbuild.c:196)
  by 0x29BF4D: index_build (index.c:2912)
 }}}

-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/4691#comment:6>
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