Hi there,
Got this while testing block migration in staging:
"""
Program terminated with signal 11, Segmentation fault.
#0 0x0000000000410cf9 in monitor_vprintf (mon=0x0, fmt=0x5ae5e7 "Start full
migration for %s\n",
ap=0x7fff1f830a40) at /home/lcapitulino/src/aliguori-queue/monitor.c:192
192 if (mon->mc && !mon->mc->print_enabled) {
"""
The problem here is that init_blk_migration() calls monitor_printf() with
a NULL 'mon' and the backtrace shows that this is true for the entire call
chain.
You probably didn't note it before because the lowest-level monitor
print function would just return if the 'mon' parameter was NULL.
A patch from me (4a29a in staging) changes a higher level monitor
function to touch 'mon' before passing it down and here's the segfault.
Now, the point is: I could give the old behavior back but I think we're
hiding a bug there. Why would you call monitor_printf() with a NULL 'mon'?
Anyways, the following patch adds the old behavior back just in case
you want to see it working...
commit 3575196202d4e54c1fc63a631ca5bd1a7778e30d
Author: Luiz Capitulino <lcapitul...@redhat.com>
Date: Thu Dec 3 15:49:16 2009 -0200
monitor: Fix block migration segfault
The monitor_vprintf() function now touches the 'mon' variable
before calling monitor_puts(), this causes block migration
to segfault as its functions call monitor_printf() with a
NULL 'mon'.
This is probably hiding the real bug, but for some reason this
has been the behavior for a long time.
We also change monitor_print_object() to use monitor_print(),
so that monitor_puts() is only called by monitor_vprintf().
Signed-off-by: Luiz Capitulino <lcapitul...@redhat.com>
diff --git a/monitor.c b/monitor.c
index b035e0b..6d0b1dd 100644
--- a/monitor.c
+++ b/monitor.c
@@ -171,9 +171,6 @@ static void monitor_puts(Monitor *mon, const char *str)
{
char c;
- if (!mon)
- return;
-
for(;;) {
c = *str++;
if (c == '\0')
@@ -189,6 +186,9 @@ static void monitor_puts(Monitor *mon, const char *str)
void monitor_vprintf(Monitor *mon, const char *fmt, va_list ap)
{
+ if (!mon)
+ return;
+
if (mon->mc && !mon->mc->print_enabled) {
qemu_error_new(QERR_UNDEFINED_ERROR);
} else {
@@ -269,7 +269,7 @@ static void monitor_print_qobject(Monitor *mon, const
QObject *data)
break;
}
- monitor_puts(mon, "\n");
+ monitor_printf(mon, "\n");
}
static void monitor_json_emitter(Monitor *mon, const QObject *data)
