Avoid calling proc_exit() in processes forked by system(). The SIGTERM handler for the startup process immediately calls proc_exit() for the duration of the restore_command, i.e., a call to system(). This system() call forks a new process to execute the shell command, and this child process inherits the parent's signal handlers. If both the parent and child processes receive SIGTERM, both will attempt to call proc_exit(). This can end badly. For example, both processes will try to remove themselves from the PGPROC shared array.
To fix this problem, this commit adds a check in StartupProcShutdownHandler() to see whether MyProcPid == getpid(). If they match, this is the parent process, and we can proc_exit() like before. If they do not match, this is a child process, and we just emit a message to STDERR (in a signal safe manner) and _exit(), thereby skipping any problematic exit callbacks. This commit also adds checks in proc_exit(), ProcKill(), and AuxiliaryProcKill() that verify they are not being called within such child processes. Suggested-by: Andres Freund Reviewed-by: Thomas Munro, Andres Freund Discussion: https://postgr.es/m/Y9nGDSgIm83FHcad%40paquier.xyz Discussion: https://postgr.es/m/20230223231503.GA743455%40nathanxps13 Backpatch-through: 11 Branch ------ REL_11_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/d0e7f95b48453703d7c740438198e47d03497cec Modified Files -------------- src/backend/postmaster/startup.c | 15 ++++++++++++++- src/backend/storage/ipc/ipc.c | 4 ++++ src/backend/storage/lmgr/proc.c | 8 ++++++++ src/backend/utils/error/elog.c | 28 ++++++++++++++++++++++++++++ src/include/utils/elog.h | 6 ++++++ 5 files changed, 60 insertions(+), 1 deletion(-)
