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# Rework SIGCHLD handler to anticipate multiple children dying while the
# handler is being executed.
#
# Without the patch if multiple SIGCHLD signals are received while the signal
# handler is being executed, the first will be left in pending state and the
# extra discarded. Due to the children processing logic in netplugd, the ones
# which were missed will never be waited, left as zombies.
#
# Implementation of the signal handler is following suggested handling in
# https://www.gnu.org/software/libc/manual/html_node/Merged-Signals.html
#
# The patch strives to change only the children wait logic in the signal
# handler, it doesn't try to enhance write call error handling or the unsafe
# call to exit/do_log. Also the formatting is left as it was in the original
# code.
--- a/main.c
+++ b/main.c
@@ -153,17 +153,29 @@ static int child_handler_pipe[2];
static void
child_handler(int sig, siginfo_t *info, void *v)
{
- struct child_exit ce;
- int ret;
- ssize_t s = 0;
+ int old_errno = errno;
assert(sig == SIGCHLD);
- ce.pid = info->si_pid;
- ret = waitpid(info->si_pid, &ce.status, 0);
- if (ret == info->si_pid)
+ while (1)
{
- s = write(child_handler_pipe[1], &ce, sizeof(ce));
+ pid_t pid;
+ int status;
+
+ do
+ {
+ errno = 0;
+ pid = waitpid(WAIT_ANY, &status, WNOHANG);
+ } while (pid <= 0 && errno == EINTR);
+
+ if (pid <= 0)
+ {
+ break;
+ }
+
+ struct child_exit ce = { .pid = pid, .status = status };
+
+ ssize_t s = write(child_handler_pipe[1], &ce, sizeof(ce));
if (s == -1)
{
@@ -171,6 +183,9 @@ child_handler(int sig, siginfo_t *info, void *v)
exit(1);
}
}
+
+ errno = old_errno;
+ return;
}
/* Poll the existing interface state, so we can catch any state
|
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