sig-monitor: handle SIGSEGV in backtrace

There was cases were the backtrace raised a segmentation
fault.

This commit also improves unblocking of signals in handler.

Change-Id: I09493d3ecc4b477660366ea213bf451c9ae7d517
Signed-off-by: José Bollo <jose.bollo@iot.bzh>

diff --git a/src/sig-monitor.c b/src/sig-monitor.c
index a92fc81..7598250 100644 (file)
--- a/src/sig-monitor.c
+++ b/src/sig-monitor.c
@@ -34,6 +34,7 @@
 
 /* local handler */
 static _Thread_local sigjmp_buf *error_handler;
+static _Thread_local int in_safe_dumpstack;
 
 /* local timers */
 static _Thread_local int thread_timer_set;
@@ -75,6 +76,24 @@ static void dumpstack(int crop, int signum)
        }
 }
 
+static void safe_dumpstack_cb(int signum, void *closure)
+{
+       int *args = closure;
+       if (signum)
+               ERROR("Can't provide backtrace: raised signal %s", strsignal(signum));
+       else
+               dumpstack(args[0], args[1]);
+}
+
+static void safe_dumpstack(int crop, int signum)
+{
+       int args[2] = { crop, signum };
+
+       in_safe_dumpstack = 1;
+       sig_monitor(0, safe_dumpstack_cb, args);
+       in_safe_dumpstack = 0;
+}
+
 /*
  * Creates a timer for the current thread
  *
@@ -146,9 +165,11 @@ static inline void timeout_delete()
 /* Handles signals that terminate the process */
 static void on_signal_terminate (int signum)
 {
-       ERROR("Terminating signal %d received: %s", signum, strsignal(signum));
-       if (signum == SIGABRT)
-               dumpstack(3, signum);
+       if (!in_safe_dumpstack) {
+               ERROR("Terminating signal %d received: %s", signum, strsignal(signum));
+               if (signum == SIGABRT)
+                       safe_dumpstack(3, signum);
+       }
        exit(1);
 }
 
@@ -157,19 +178,19 @@ static void on_signal_error(int signum)
 {
        sigset_t sigset;
 
+       if (in_safe_dumpstack)
+               longjmp(*error_handler, signum);
+
        ERROR("ALERT! signal %d received: %s", signum, strsignal(signum));
        if (error_handler == NULL && signum == SIG_FOR_TIMER)
                return;
 
-       dumpstack(3, signum);
+       safe_dumpstack(3, signum);
 
        // unlock signal to allow a new signal to come
-       if (error_handler != NULL) {
-               sigemptyset(&sigset);
-               sigaddset(&sigset, signum);
-               sigprocmask(SIG_UNBLOCK, &sigset, 0);
+       if (error_handler != NULL)
                longjmp(*error_handler, signum);
-       }
+
        ERROR("Unmonitored signal %d received: %s", signum, strsignal(signum));
        exit(2);
 }
@@ -178,9 +199,14 @@ static void on_signal_error(int signum)
 static int install(void (*handler)(int), int *signals)
 {
        int result = 1;
+       struct sigaction sa;
+
+       sa.sa_handler = handler;
+       sigemptyset(&sa.sa_mask);
+       sa.sa_flags = SA_NODEFER;
        while(*signals > 0) {
-               if (signal(*signals, handler) == SIG_ERR) {
-                       ERROR("failed to install signal handler for signal %s", strsignal(*signals));
+               if (sigaction(*signals, &sa, NULL) < 0) {
+                       ERROR("failed to install signal handler for signal %s: %m", strsignal(*signals));
                        result = 0;
                }
                signals++;