From: Johannes Sixt Date: Tue, 02 Aug 2016 05:53:31 GMT Subject: Re: [PATCH v3 06/10] run-command: add clean_on_exit_handler Message-ID: In-Reply-To: Am 01.08.2016 um 13:14 schrieb Lars Schneider: >> On 30 Jul 2016, at 11:50, Johannes Sixt 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