Re: [PATCH v3 06/10] run-command: add clean_on_exit_handler

Am 01.08.2016 um 13:14 schrieb Lars Schneider:
 >> On 30 Jul 2016, at 11:50, Johannes Sixt <j6t@kdbg.org> wrote:
 >> Am 30.07.2016 um 01:37 schrieb larsxschneider@gmail.com:
 >>> static struct child_to_clean *children_to_clean;
 >>> @@ -30,6 +31,8 @@ static void cleanup_children(int sig, int in_signal)
 >>> {
 >>> 	while (children_to_clean) {
 >>> 		struct child_to_clean *p = children_to_clean;
 >>> +		if (p->clean_on_exit_handler)
 >>> +			p->clean_on_exit_handler(p->pid);
 >>
 >> This summons demons. cleanup_children() is invoked from a signal
 >> handler. In this case, it can call only async-signal-safe functions.
 >> It does not look like the handler that you are going to install
 >> later will take note of this caveat!
 >>
 >>> 		children_to_clean = p->next;
 >>> 		kill(p->pid, sig);
 >>> 		if (!in_signal)
 >>
 >> The condition that we see here in the context protects free(p)
 >> (which is not async-signal-safe). Perhaps the invocation of the new
 >> callback should be skipped in the same manner when this is called
 >> from a signal handler? 507d7804 (pager: don't use unsafe functions
 >> in signal handlers) may be worth a look.
 >
 > Thanks a lot of pointing this out to me!
 >
 > Do I get it right that after the signal "SIGTERM" I can do a cleanup
 > and don't need to worry about any function calls but if I get any
 > other signal then I can only perform async-signal-safe calls?

No. SIGTERM is not special.

Perhaps you were misled by the SIGTERM mentioned in cleanup_children_on_exit()? This function is invoked on regular exit (not from a signal). SIGTERM is used in this case to terminate children that are still lingering around.

 > If this is correct, then the following solution would work great:
 >
 > 		if (!in_signal && p->clean_on_exit_handler)
 > 			p->clean_on_exit_handler(p->pid);

This should work nevertheless because in_signal is set when the function is invoked from a signal handler (of any signal that is caught) via cleanup_children_on_signal().

-- Hannes