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a8b330ffb6
The comments in dsa.c suggested that areas were owned by resource
owners, but it was not in fact tracked explicitly. The DSM attachments
held by the dsa were owned by resource owners, but not the area
itself. That led to confusion if you used one resource owner to
attach or create the area, but then switched to a different resource
owner before allocating or even just accessing the allocations in the
area with dsa_get_address(). The additional DSM segments associated
with the area would get owned by a different resource owner than the
initial segment. To fix, add an explicit 'resowner' field to
dsa_area. It replaces the 'mapping_pinned' flag; resowner == NULL now
indicates that the mapping is pinned.
This is arguably a bug fix, but I'm not backpatching because it
doesn't seem to be a live bug in the back branches. In 'master', it is
a bug because commit b8bff07daa made ResourceOwners more strict so
that you are no longer allowed to remember new resources in a
ResourceOwner after you have started to release it. Merely accessing a
dsa pointer might need to attach a new DSM segment, and before this
commit it was temporarily remembered in the current owner for a very
brief period even if the DSA was pinned. And that could happen in
AtEOXact_PgStat(), which is called after the owner is already released.
Reported-by: Alexander Lakhin
Reviewed-by: Alexander Lakhin, Thomas Munro, Andres Freund
Discussion: https://www.postgresql.org/message-id/11b70743-c5f3-3910-8e5b-dd6c115ff829%40gmail.com
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.