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It turns out that on some platforms (at least current macOS, NetBSD, OpenBSD) semget(2) will return EINVAL if there is a pre-existing semaphore set with the same key and too few semaphores. Our code expects EEXIST in that case and treats EINVAL as a hard failure, resulting in failure during initdb or postmaster start. POSIX does document EINVAL for too-few-semaphores-in-set, and is silent on its priority relative to EEXIST, so this behavior arguably conforms to spec. Nonetheless it's quite problematic because EINVAL is also documented to mean that nsems is greater than the system's limit on the number of semaphores per set (SEMMSL). If that is where the problem lies, retrying would just become an infinite loop. To resolve this contradiction, retry after EINVAL, but also install a loop limit that will make us give up regardless of the specific errno after trying 1000 different keys. (1000 is a pretty arbitrary number, but it seems like it should be sufficient.) I like this better than the previous infinite-looping behavior, since it will also keep us out of trouble if (say) we get EACCES due to a system-level permissions problem rather than anything to do with a specific semaphore set. This problem has only been observed in the field in PG 17, which uses a higher nsems value than other branches (cf.38da05346,810a8b1c8). That makes it possible to get the failure if a new v17 postmaster has a key collision with an existing postmaster of another branch. In principle though, we might see such a collision against a semaphore set created by some other application, in which case all branches are vulnerable on these platforms. Hence, backpatch. Reported-by: Gavin Panella <gavinpanella@gmail.com> Author: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/CALL7chmzY3eXHA7zHnODUVGZLSvK3wYCSP0RmcDFHJY8f28Q3g@mail.gmail.com Backpatch-through: 13
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/.