mirror of
https://github.com/postgres/postgres.git
synced 2025-05-12 16:21:30 +03:00
a73c8caea4
There's a very old race condition in our code to see whether a pre-existing shared memory segment is still in use by a conflicting postmaster: it's possible for the other postmaster to remove the segment in between our shmctl() and shmat() calls. It's a narrow window, and there's no risk unless both postmasters are using the same port number, but that's possible during parallelized "make check" tests. (Note that while the TAP tests take some pains to choose a randomized port number, pg_regress doesn't.) If it does happen, we treated that as an unexpected case and errored out. To fix, allow EINVAL to be treated as segment-not-present, and the same for EIDRM on Linux. AFAICS, the considerations here are basically identical to the checks for acceptable shmctl() failures, so I documented and coded it that way. While at it, adjust PGSharedMemoryAttach's API to remove its undocumented dependency on UsedShmemSegAddr in favor of passing the attach address explicitly. This makes it easier to be sure we're using a null shmaddr when probing for segment conflicts (thus avoiding questions about what EINVAL means). I don't think there was a bug there, but it required fragile assumptions about the state of UsedShmemSegAddr during PGSharedMemoryIsInUse. Commit c09850992 may have made this failure more probable by applying the conflicting-segment tests more often. Hence, back-patch to all supported branches, as that was. Discussion: https://postgr.es/m/22224.1557340366@sss.pgh.pa.us
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. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download 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 may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.