Messages in this thread Patch in this message | | | Date | Thu, 6 Feb 2003 17:40:47 -0500 | From | Daniel Jacobowitz <> | Subject | Ptrace updates: has_stopped_jobs [1/5] |
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I posted this patch a couple of weeks ago, here it is again. The basic problem it's solving is this: suppose you have GDB debugging an application, using the new PTRACE_EVENT_FORK. The application forks. There can be a point where GDB resumes the parent, which gets scheduled, and exits, before GDB gets a chance to resume the child. has_stopped_jobs causes the kernel to decide the still-stopped-in-GDB child (which will be an orphaned pgrp) is going to be lost, so it sends a SIGHUP and SIGCONT to it, confusing GDB terribly. Normally those signals wouldn't be sent.
The longer explanation:
POSIX has this terribly useful thing to say:
# If the exit of the process causes a process group to become orphaned, and if # any member of the newly-orphaned process group is stopped, then a SIGHUP # signal followed by a SIGCONT signal shall be sent to each process in the # newly-orphaned process group.
The Rationale is at least a little chattier. See
http://www.opengroup.org/onlinepubs/007904975/functions/exit.html#tag_03_131 if you want to read it.
Basically, this is so that a stopped process group won't unintentionally stay stopped when its shell no longer has a connection to it. For whatever that's worth.
I think this patch is well within the spirit of that definition. If a process is stopped, but there is a debugger attached to it and the stopping signal is not one that would normally stop the process, then don't count it as a stopped job. Without this, when you continue past a fork() call and the parent quickly exits, the child will get an unaccountable SIGHUP.
It's not perfect, of course - the application might be SIG_IGN'ing SIGTSTP, but stopped in the debugger for it anyway. It's not worth being that complicated here, though.
# -------------------------------------------- # 03/01/18 drow@nevyn.them.org 1.957 # Tweak has_stopped_jobs for use with debugging # --------------------------------------------
diff -Nru a/kernel/exit.c b/kernel/exit.c --- a/kernel/exit.c Thu Feb 6 16:57:39 2003 +++ b/kernel/exit.c Thu Feb 6 16:57:39 2003 @@ -203,6 +203,17 @@ for_each_task_pid(pgrp, PIDTYPE_PGID, p, l, pid) { if (p->state != TASK_STOPPED) continue; + + /* If p is stopped by a debugger on a signal that won't + stop it, then don't count p as stopped. This isn't + perfect but it's a good approximation. */ + if (unlikely (p->ptrace) + && p->exit_code != SIGSTOP + && p->exit_code != SIGTSTP + && p->exit_code != SIGTTOU + && p->exit_code != SIGTTIN) + continue; + retval = 1; break; } -- Daniel Jacobowitz MontaVista Software Debian GNU/Linux Developer - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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