On Fri, 12 May 2023 15:24:19 GMT, Volker Simonis <simo...@openjdk.org> wrote:
> Since JDK13, executing commands in a sub-process defaults to the so called > `POSIX_SPAWN` launching mechanism (i.e. > `-Djdk.lang.Process.launchMechanism=POSIX_SPAWN`) on Linux. This works by > using `posix_spawn(3)` to firstly start a tiny helper program called > `jspawnhelper` in a subprocess. In a second step, `jspawnhelper` reads the > command data from the parent Java process over a Unix pipe and finally > executes (i.e. `execvp(3)`) the requested command. > > In cases where the parent process terminates abnormally before `jspawnhelper` > has read all the expected data from the pipe, `jspawnhelper` will block > indefinitely on the reading end of the pipe. This is especially harmful if > the parent process had open sockets, because in that case, the forked > `jspawnhelper` process will inherit them and keep all the corresponding ports > open effectively preventing other processes to bind to them. Notice that this > is not an abstract scenario. We've observed this regularly in production with > services which couldn't be restarted after a crash after migrating to JDK 17. > > The fix of the issue is rather trivial. `jspawnhelper` has to close its > writing end of the pipe which connects it with the parent Java process > *before* starting to read from that pipe such that reads from the pipe can > immediately return with EOF if the parent process terminates abnormally. > > Also did some cleanup: > - in `jspawnhelper.c` correctly chek the result of `readFully()` > - in `ProcessImpl_md.c` use `restartableWrite()` instead of `write()` to > write the command data from the parent process to `jspawnhelper` > - in `childproc.{c,h}` remove remaining traces of `MODE_CLONE` because > that's long gone. I wonder if @Martin-Buchholz is able to look at this one? My concern with changes like this is that they fix an issue but then have unexpected side-effects themselves. ------------- PR Comment: https://git.openjdk.org/jdk/pull/13956#issuecomment-1549138815