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We need to hold interrupts across most of the smgr.c/md.c functions, as otherwise interrupt processing, e.g. due to a < ERROR elog/ereport, can trigger procsignal processing, which in turn can trigger smgrreleaseall(). As the relevant code is not reentrant, we quickly end up in a bad situation. The only reason we haven't noticed this before is that there is only one non-error ereport called in affected routines, in register_dirty_segments(), and that one is extremely rarely reached. If one enables fd.c's FDDEBUG it's easy to reproduce crashes. It seems better to put the HOLD_INTERRUPTS()/RESUME_INTERRUPTS() in smgr.c, instead of trying to push them down to md.c where possible: For one, every smgr implementation would be vulnerable, for another, a good bit of smgr.c code itself is affected too. Eventually we might want a more targeted solution, allowing e.g. a networked smgr implementation to be interrupted, but many other, more complicated, problems would need to be fixed for that to be viable (e.g. smgr.c is often called with interrupts already held). One could argue this should be backpatched, but the existing < ERROR elog/ereports that can be reached with unmodified sources are unlikely to be reached. On balance the risk of backpatching seems higher than the gain - at least for now. Reviewed-by: Noah Misch <noah@leadboat.com> Reviewed-by: Thomas Munro <thomas.munro@gmail.com> Discussion: https://postgr.es/m/3vae7l5ozvqtxmd7rr7zaeq3qkuipz365u3rtim5t5wdkr6f4g@vkgf2fogjirl
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.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
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/.