threads: backup commit for signal safe pthread_create

Knot.files

@@ -146,6 +146,8 @@ src/contrib/string.h
 src/contrib/strtonum.h
 src/contrib/time.c
 src/contrib/time.h
+src/contrib/threads.c
+src/contrib/threads.h
 src/contrib/toeplitz.h
 src/contrib/tolower.h
 src/contrib/trim.h

src/contrib/Makefile.inc

@@ -61,6 +61,8 @@ libcontrib_la_SOURCES = \
 	contrib/strtonum.h			\
 	contrib/time.c				\
 	contrib/time.h				\
+	contrib/threads.c			\
+	contrib/threads.h			\
 	contrib/toeplitz.h			\
 	contrib/tolower.h			\
 	contrib/trim.h				\

src/contrib/threads.c

@@ -0,0 +1,69 @@
+/*  Copyright (C) 2024 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include "contrib/threads.h"
+
+typedef struct {
+	const struct sigaction *sa;
+	const sigset_t *sm;
+	void *(*routine)(void *);
+	void *arg;
+	const int *signals;
+	int nsignals;
+} sigsafe_arg_t;
+
+static void *thread_create_sigsafe__impl(void *arg)
+{
+	sigsafe_arg_t *sarg = arg;
+
+	// first set handlers, then unblock - order matters!
+	for (int i = 0; i < sarg->nsignals; ++i) {
+		sigaction(sarg->signals[i], sarg->sa, NULL);
+	}
+	pthread_sigmask(SIG_SETMASK, sarg->sm, NULL);
+
+	return sarg->routine(sarg->arg);
+}
+
+int thread_create_sigsafe(pthread_t *restrict thr,
+			  const pthread_attr_t *restrict attr,
+			  const struct sigaction *sa,
+			  const sigset_t *sm,
+			  const int *signals,
+			  int nsignals,
+			  void *(*routine)(void *),
+			  void *restrict arg)
+{
+	sigset_t mask;
+	sigset_t oldmask;
+	sigfillset(&mask);
+	sigdelset(&mask, SIGBUS);
+	sigdelset(&mask, SIGFPE);
+	sigdelset(&mask, SIGILL);
+	sigdelset(&mask, SIGSEGV);
+
+	// block all blockable signals
+	pthread_sigmask(SIG_SETMASK, &mask, &oldmask);
+
+	// set desired sigmask and signal handler inside the thread through a wrapper function
+	sigsafe_arg_t sarg = { sa, sm, routine, arg, signals, nsignals };
+	int ret = pthread_create(thr, attr, thread_create_sigsafe__impl, &sarg);
+
+	// restore original sigmask
+	pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
+
+	return ret;
+}

src/contrib/threads.h

@@ -0,0 +1,43 @@
+/*  Copyright (C) 2024 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <pthread.h>
+#include <signal.h>
+
+/*!
+ * \brief Spawn a new thread with different signal handling parameters without
+ * risk of signal related race conditions.
+ *
+ * @param thr pthread_t structure
+ * @param attr pthread_attr_t structure
+ * @param sa struct sigaction handler to be used within the thread
+ * @param sm sigset_t signal mask to be used within the thread
+ * @param signals an array of signal numbers to which sigaction should be applied
+ * @param nsignals ARR_LEN(signals)
+ * @param routine thread entry function
+ * @param arg thread argument
+ * @returns return value of pthread_create
+ */
+int thread_create_sigsafe(pthread_t *restrict thr,
+			  const pthread_attr_t *restrict attr,
+			  const struct sigaction *sa,
+			  const sigset_t *sm,
+			  const int *signals,
+			  int nsignals,
+			  void *(*routine)(void *),
+			  void *restrict arg);