[ovs-dev] [PATCH] fatal-signal: Log backtrace when no monitor daemon.

William Tu u9012063 at gmail.com
Mon Mar 23 15:16:30 UTC 2020


Currently the backtrace logging is only available when monitor
daemon is running.  This patch enables backtrace logging when
no monitor daemon exists.  At signal handling context, it detects
whether monitor daemon exists.  If not, write directly the backtrace
to the vlog fd.  Note that using VLOG_* macro doesn't work due to
it's buffer I/O, so this patch directly issue write() syscall to
the file descriptor.

Signed-off-by: William Tu <u9012063 at gmail.com>
---
For some system we stop using monitor daemon and use systemd to monitor
ovs-vswitchd, thus need this patch. Example of ovs-vswitchd.log:
2020-03-23T14:42:12.949Z|00049|memory|INFO|175332 kB peak resident set size after 10.0 seconds
2020-03-23T14:42:12.949Z|00050|memory|INFO|handlers:2 ports:3 revalidators:2 rules:8 udpif keys:8
SIGSEGV detected, backtrace:
0x0000000000486969 <fatal_signal_handler+0x49>
0x00007f7f5e57f4b0 <killpg+0x40>
0x000000000047daa8 <pmd_thread_main+0x238>
0x0000000000504edd <ovsthread_wrapper+0x7d>
0x00007f7f5f0476ba <start_thread+0xca>
0x00007f7f5e65141d <clone+0x6d>
0x0000000000000000 <+0x0>

travis:
https://travis-ci.org/github/williamtu/ovs-travis/builds/665909423
---
 include/openvswitch/vlog.h |  3 +++
 lib/daemon-private.h       |  1 +
 lib/daemon-unix.c          |  2 +-
 lib/fatal-signal.c         | 22 +++++++++++++++++++++-
 lib/vlog.c                 |  6 ++++++
 5 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/include/openvswitch/vlog.h b/include/openvswitch/vlog.h
index 19da4ab62320..476bf3d6d5b4 100644
--- a/include/openvswitch/vlog.h
+++ b/include/openvswitch/vlog.h
@@ -143,6 +143,9 @@ void vlog_set_syslog_method(const char *method);
 /* Configure syslog target. */
 void vlog_set_syslog_target(const char *target);
 
+/* Return the log_fd. */
+int vlog_get_fd(void);
+
 /* Initialization. */
 void vlog_init(void);
 void vlog_enable_async(void);
diff --git a/lib/daemon-private.h b/lib/daemon-private.h
index 4e0667601001..2b90e004235c 100644
--- a/lib/daemon-private.h
+++ b/lib/daemon-private.h
@@ -20,6 +20,7 @@
 extern bool detach;
 extern char *pidfile;
 extern int daemonize_fd;
+extern bool monitor;
 
 char *make_pidfile_name(const char *name);
 
diff --git a/lib/daemon-unix.c b/lib/daemon-unix.c
index 7e48630f0e93..e073b894ab49 100644
--- a/lib/daemon-unix.c
+++ b/lib/daemon-unix.c
@@ -80,7 +80,7 @@ int daemonize_fd = -1;
 
 /* --monitor: Should a supervisory process monitor the daemon and restart it if
  * it dies due to an error signal? */
-static bool monitor;
+bool monitor;
 
 /* --user: Only root can use this option. Switch to new uid:gid after
  * initially running as root.  */
diff --git a/lib/fatal-signal.c b/lib/fatal-signal.c
index ba7f5bfd314d..35e26de97b84 100644
--- a/lib/fatal-signal.c
+++ b/lib/fatal-signal.c
@@ -187,7 +187,27 @@ send_backtrace_to_monitor(void) {
         dep++;
     }
 
-    ignore(write(daemonize_fd, unw_bt, dep * sizeof(struct unw_backtrace)));
+    if (monitor) {
+        ignore(write(daemonize_fd, unw_bt,
+                     dep * sizeof(struct unw_backtrace)));
+    } else {
+        /* Since there is no monitor daemon running, write backtrace
+         * in current process.  This is not asyn-signal-safe due to
+         * use of snprintf().
+         */
+        char str[] = "SIGSEGV detected, backtrace:\n";
+        ignore(write(vlog_get_fd(), str, strlen(str)));
+
+        for (int i = 0; i < dep; i++) {
+            char line[64];
+
+            snprintf(line, 64, "0x%016"PRIxPTR" <%s+0x%"PRIxPTR">\n",
+                     unw_bt[i].ip,
+                     unw_bt[i].func,
+                     unw_bt[i].offset);
+            ignore(write(vlog_get_fd(), line, strlen(line)));
+        }
+    }
 }
 #else
 static inline void
diff --git a/lib/vlog.c b/lib/vlog.c
index 559943d87937..502b33fc831e 100644
--- a/lib/vlog.c
+++ b/lib/vlog.c
@@ -612,6 +612,12 @@ vlog_set_syslog_target(const char *target)
     ovs_rwlock_unlock(&pattern_rwlock);
 }
 
+int
+vlog_get_fd(void)
+{
+    return log_fd;
+}
+
 /* Returns 'false' if 'facility' is not a valid string. If 'facility'
  * is a valid string, sets 'value' with the integer value of 'facility'
  * and returns 'true'. */
-- 
2.7.4



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