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Commit29ddb54

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Fix inconsistent out-of-memory error reporting in dsa.c.
Commit16be2fd introduced the flag DSA_ALLOC_NO_OOM to control whetherthe DSA allocator would raise an error or return InvalidDsaPointer onfailure to allocate. One edge case was not handled correctly: if wefail to allocate an internal "span" object for a large allocation, wewould always return InvalidDsaPointer regardless of the flag; a callernot expecting that could then dereference a null pointer.This is a plausible explanation for a one-off report of a segfault.Remove a redundant pair of braces so that all three stanzas that handleDSA_ALLOC_NO_OOM match in style, for visual consistency.While fixing inconsistencies, if FreePageManagerGet() can't supply thepages that our book-keeping says it should be able to supply, then weshould always report a FATAL error. Previously we treated that as aregular allocation failure in one code path, but as a FATAL conditionin another.Back-patch to 10, where dsa.c landed.Author: Thomas MunroReported-by: Jakub GlapaDiscussion:https://postgr.es/m/CAEepm=2oPqXxyWQ-1o60tpOLrwkw=VpgNXqqF1VN2EyO9zKGQw@mail.gmail.com
1 parent9e138a4 commit29ddb54

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1 file changed

+16
-8
lines changed
  • src/backend/utils/mmgr

1 file changed

+16
-8
lines changed

‎src/backend/utils/mmgr/dsa.c

Lines changed: 16 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -693,7 +693,16 @@ dsa_allocate_extended(dsa_area *area, size_t size, int flags)
693693
/* Obtain a span object. */
694694
span_pointer=alloc_object(area,DSA_SCLASS_BLOCK_OF_SPANS);
695695
if (!DsaPointerIsValid(span_pointer))
696+
{
697+
/* Raise error unless asked not to. */
698+
if ((flags&DSA_ALLOC_NO_OOM)==0)
699+
ereport(ERROR,
700+
(errcode(ERRCODE_OUT_OF_MEMORY),
701+
errmsg("out of memory"),
702+
errdetail("Failed on DSA request of size %zu.",
703+
size)));
696704
returnInvalidDsaPointer;
705+
}
697706

698707
LWLockAcquire(DSA_AREA_LOCK(area),LW_EXCLUSIVE);
699708

@@ -790,12 +799,10 @@ dsa_allocate_extended(dsa_area *area, size_t size, int flags)
790799
{
791800
/* Raise error unless asked not to. */
792801
if ((flags&DSA_ALLOC_NO_OOM)==0)
793-
{
794802
ereport(ERROR,
795803
(errcode(ERRCODE_OUT_OF_MEMORY),
796804
errmsg("out of memory"),
797805
errdetail("Failed on DSA request of size %zu.",size)));
798-
}
799806
returnInvalidDsaPointer;
800807
}
801808

@@ -1669,13 +1676,14 @@ ensure_active_superblock(dsa_area *area, dsa_area_pool *pool,
16691676
return false;
16701677
}
16711678
}
1679+
/*
1680+
* This shouldn't happen: get_best_segment() or make_new_segment()
1681+
* promised that we can successfully allocate npages.
1682+
*/
16721683
if (!FreePageManagerGet(segment_map->fpm,npages,&first_page))
1673-
{
1674-
LWLockRelease(DSA_AREA_LOCK(area));
1675-
if (size_class!=DSA_SCLASS_BLOCK_OF_SPANS)
1676-
dsa_free(area,span_pointer);
1677-
return false;
1678-
}
1684+
elog(FATAL,
1685+
"dsa_allocate could not find %zu free pages for superblock",
1686+
npages);
16791687
LWLockRelease(DSA_AREA_LOCK(area));
16801688

16811689
/* Compute the start of the superblock. */

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