Fix incorrect sentinel byte logic in GenerationRealloc()
This only affects MEMORY_CONTEXT_CHECKING builds.
This fixes an off-by-one issue in GenerationRealloc() where the
fast-path code which tries to reuse the existing allocation if the
existing chunk is >= the new requested size. The code there thought it
was always ok to use the existing chunk, but when oldsize == size there
isn't enough space to store the sentinel byte. If both sizes matched
exactly set_sentinel() would overwrite the first byte beyond the chunk
and then subsequent GenerationRealloc() calls could then fail the
Assert(chunk->requested_size < oldsize) check which is trying to ensure
the chunk is large enough to store the sentinel.
The same issue does not exist in aset.c as the sentinel checking code
only adds a sentinel byte if there's enough space in the chunk.
Reported-by: Alexander Lakhin <[email protected]>
Discussion: https://postgr.es/m/[email protected]
Backpatch-through: 16, where the problem was introduced by 0e480385e
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/97651b0139cfa511eaf063b60c900c2ba81b8ba2
Modified Files
--------------
src/backend/utils/mmgr/generation.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
