vmm: Avoid zombie sigwinch_listener processes #6208
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Ah sorry, I see you have subsystem: prefixes. I've added vmm: to match the other commits affecting vmm/src/sigwinch_listener.rs. (There doesn't seem to be any consistency about whether the summary line following the subsystem prefix has an initial capital or not, but capitalised seems to be slightly more prevalent so I went with that.) |
arachsys
changed the title
It's quite a handy trick if you genuinely don't need the exit status of any children. /bin/init on a POSIX system can just consist of signal(SIGCHLD, SIG_IGN);
pause();which is fun. :) |
When a guest running on a terminal reboots, the sigwinch_listener subprocess exits and a new one restarts. The parent never wait()s for children, so the old subprocess remains as a zombie. With further reboots, more and more zombies build up. As there are no other children for which we want the exit status, the easiest fix is to take advantage of the implicit reaping specified by POSIX when we set the disposition of SIGCHLD to SIG_IGN. For this to work, we also need to set the correct default exit signal of SIGCHLD when using clone3() CLONE_CLEAR_SIGHAND. Unlike the fallback fork() path, clone_args::default() initialises the exit signal to zero, which results in a child with non-standard reaping behaviour. Signed-off-by: Chris Webb <chris@arachsys.com>
When a guest running on a terminal reboots, the
sigwinch_listenersubprocess exits and a new one restarts. The parent never wait()s for children, so the old subprocess remains as a zombie. With further reboots, more and more zombies build up.As there are no other children whose exit status we want, the easiest fix is to take advantage of the implicit reaping specified by POSIX when we set the disposition of
SIGCHLDtoSIG_IGN.For this to work, we also need to set the correct default exit signal of
SIGCHLDwhen usingclone3() CLONE_CLEAR_SIGHAND. Unlike the fallbackfork()path,clone_args::default()initialises the exit signal to zero, which results in a child with non-standard reaping behaviour.