The monitor_cur_hmp() function will acquire/release mutex locks, which
will trigger trace probes, which can in turn trigger qemu_log() calls.
vreport() calls monitor_cur() multiple times through its execution
both directly and indirectly via error_vprintf().
The result is that the prefix information printed by vreport() gets
interleaved with qemu_log() output, when run outside the context of
an HMP command dispatcher. This can be seen with:
$ qemu-system-x86_64 \
-msg timestamp=on,guest-name=on \
-display none \
-object tls-creds-x509,id=f,dir=fish \
-name fish \
-d trace:qemu_mutex*
2025-09-10T16:30:42.514374Z qemu_mutex_unlock released mutex 0x560b0339b4c0 (/var/home/berrange/src/virt/qemu/include/qemu/lockable.h:56)
2025-09-10T16:30:42.514400Z qemu_mutex_lock waiting on mutex 0x560b033983e0 (/var/home/berrange/src/virt/qemu/include/qemu/lockable.h:56)
2025-09-10T16:30:42.514402Z qemu_mutex_locked taken mutex 0x560b033983e0 (/var/home/berrange/src/virt/qemu/include/qemu/lockable.h:56)
2025-09-10T16:30:42.514404Z qemu_mutex_unlock released mutex 0x560b033983e0 (/var/home/berrange/src/virt/qemu/include/qemu/lockable.h:56)
2025-09-10T16:30:42.516716Z qemu_mutex_lock waiting on mutex 0x560b03398560 (../monitor/monitor.c:91)
2025-09-10T16:30:42.516723Z qemu_mutex_locked taken mutex 0x560b03398560 (../monitor/monitor.c:91)
2025-09-10T16:30:42.516726Z qemu_mutex_unlock released mutex 0x560b03398560 (../monitor/monitor.c:96)
2025-09-10T16:30:42.516728Z qemu_mutex_lock waiting on mutex 0x560b03398560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842057Z qemu_mutex_locked taken mutex 0x564f5e401560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842058Z qemu_mutex_unlock released mutex 0x564f5e401560 (../monitor/monitor.c:96)
2025-09-10T16:31:04.842055Z 2025-09-10T16:31:04.842060Z qemu_mutex_lock waiting on mutex 0x564f5e401560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842061Z qemu_mutex_locked taken mutex 0x564f5e401560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842062Z qemu_mutex_unlock released mutex 0x564f5e401560 (../monitor/monitor.c:96)
2025-09-10T16:31:04.842064Z qemu_mutex_lock waiting on mutex 0x564f5e401560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842065Z qemu_mutex_locked taken mutex 0x564f5e401560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842066Z qemu_mutex_unlock released mutex 0x564f5e401560 (../monitor/monitor.c:96)
fish 2025-09-10T16:31:04.842068Z qemu_mutex_lock waiting on mutex 0x564f5e401560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842069Z qemu_mutex_locked taken mutex 0x564f5e401560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842070Z qemu_mutex_unlock released mutex 0x564f5e401560 (../monitor/monitor.c:96)
2025-09-10T16:31:04.842072Z qemu_mutex_lock waiting on mutex 0x564f5e401560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842097Z qemu_mutex_locked taken mutex 0x564f5e401560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842099Z qemu_mutex_unlock released mutex 0x564f5e401560 (../monitor/monitor.c:96)
qemu-system-x86_64:2025-09-10T16:31:04.842100Z qemu_mutex_lock waiting on mutex 0x564f5e401560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842102Z qemu_mutex_locked taken mutex 0x564f5e401560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842103Z qemu_mutex_unlock released mutex 0x564f5e401560 (../monitor/monitor.c:96)
2025-09-10T16:31:04.842105Z qemu_mutex_lock waiting on mutex 0x564f5e401560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842106Z qemu_mutex_locked taken mutex 0x564f5e401560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842107Z qemu_mutex_unlock released mutex 0x564f5e401560 (../monitor/monitor.c:96)
Unable to access credentials fish/ca-cert.pem: No such file or directory2025-09-10T16:31:04.842109Z qemu_mutex_lock waiting on mutex 0x564f5e401560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842110Z qemu_mutex_locked taken mutex 0x564f5e401560 (../monitor/monitor.c:91)
2025-09-10T16:31:04.842111Z qemu_mutex_unlock released mutex 0x564f5e401560 (../monitor/monitor.c:96)
To avoid this interleaving (as well as reduce the huge number of
mutex lock/unlock calls) we need to ensure that monitor_cur_is_hmp()
is only called once at the start of vreport(), and if no HMP is
present, no further monitor APIs can be called.
This implies error_[v]printf() cannot be called from vreport().
Instead we must introduce error_[v]printf_mon() which accept a
pre-acquired Monitor object. In some cases, however, fprintf
can be called directly as output will never be directed to the
monitor.
$ qemu-system-x86_64 \
-msg timestamp=on,guest-name=on \
-display none \
-object tls-creds-x509,id=f,dir=fish \
-name fish \
-d trace:qemu_mutex*
2025-09-10T16:31:22.701691Z qemu_mutex_unlock released mutex 0x5626fd3b84c0 (/var/home/berrange/src/virt/qemu/include/qemu/lockable.h:56)
2025-09-10T16:31:22.701728Z qemu_mutex_lock waiting on mutex 0x5626fd3b53e0 (/var/home/berrange/src/virt/qemu/include/qemu/lockable.h:56)
2025-09-10T16:31:22.701730Z qemu_mutex_locked taken mutex 0x5626fd3b53e0 (/var/home/berrange/src/virt/qemu/include/qemu/lockable.h:56)
2025-09-10T16:31:22.701732Z qemu_mutex_unlock released mutex 0x5626fd3b53e0 (/var/home/berrange/src/virt/qemu/include/qemu/lockable.h:56)
2025-09-10T16:31:22.703989Z qemu_mutex_lock waiting on mutex 0x5626fd3b5560 (../monitor/monitor.c:91)
2025-09-10T16:31:22.703996Z qemu_mutex_locked taken mutex 0x5626fd3b5560 (../monitor/monitor.c:91)
2025-09-10T16:31:22.703999Z qemu_mutex_unlock released mutex 0x5626fd3b5560 (../monitor/monitor.c:96)
2025-09-10T16:31:22.704000Z fish qemu-system-x86_64: Unable to access credentials fish/ca-cert.pem: No such file or directory
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
util/error-report.c | 63 ++++++++++++++++++++++++++++++---------------
1 file changed, 42 insertions(+), 21 deletions(-)
diff --git a/util/error-report.c b/util/error-report.c
index f3aa24ec22..b34a2bc7bc 100644
--- a/util/error-report.c
+++ b/util/error-report.c
@@ -32,9 +32,9 @@ const char *error_guest_name;
/*
* Print to the current human monitor if we have one, else to stderr.
*/
-int error_vprintf(const char *fmt, va_list ap)
+static int G_GNUC_PRINTF(2, 0)
+error_vprintf_mon(Monitor *cur_mon, const char *fmt, va_list ap)
{
- Monitor *cur_mon = monitor_cur();
/*
* This will return -1 if 'cur_mon' is NULL, or is QMP.
* IOW this will only print if in HMP, otherwise we
@@ -47,13 +47,33 @@ int error_vprintf(const char *fmt, va_list ap)
return ret;
}
+/*
+ * Print to the current human monitor if we have one, else to stderr.
+ */
+static int G_GNUC_PRINTF(2, 3)
+error_printf_mon(Monitor *cur_mon, const char *fmt, ...)
+{
+ va_list ap;
+ int ret;
+
+ va_start(ap, fmt);
+ ret = error_vprintf_mon(cur_mon, fmt, ap);
+ va_end(ap);
+ return ret;
+}
+
+int error_vprintf(const char *fmt, va_list ap)
+{
+ return error_vprintf_mon(monitor_cur(), fmt, ap);
+}
+
int error_printf(const char *fmt, ...)
{
va_list ap;
int ret;
va_start(ap, fmt);
- ret = error_vprintf(fmt, ap);
+ ret = error_vprintf_mon(monitor_cur(), fmt, ap);
va_end(ap);
return ret;
}
@@ -156,34 +176,34 @@ void loc_set_file(const char *fname, int lno)
/*
* Print current location to current monitor if we have one, else to stderr.
*/
-static void print_loc(void)
+static void print_loc(Monitor *cur)
{
const char *sep = "";
int i;
const char *const *argp;
- if (!monitor_cur() && g_get_prgname()) {
- error_printf("%s:", g_get_prgname());
+ if (!cur && g_get_prgname()) {
+ fprintf(stderr, "%s:", g_get_prgname());
sep = " ";
}
switch (cur_loc->kind) {
case LOC_CMDLINE:
argp = cur_loc->ptr;
for (i = 0; i < cur_loc->num; i++) {
- error_printf("%s%s", sep, argp[i]);
+ error_printf_mon(cur, "%s%s", sep, argp[i]);
sep = " ";
}
- error_printf(": ");
+ error_printf_mon(cur, ": ");
break;
case LOC_FILE:
- error_printf("%s:", (const char *)cur_loc->ptr);
+ error_printf_mon(cur, "%s:", (const char *)cur_loc->ptr);
if (cur_loc->num) {
- error_printf("%d:", cur_loc->num);
+ error_printf_mon(cur, "%d:", cur_loc->num);
}
- error_printf(" ");
+ error_printf_mon(cur, " ");
break;
default:
- error_printf("%s", sep);
+ error_printf_mon(cur, "%s", sep);
}
}
@@ -204,34 +224,35 @@ real_time_iso8601(void)
G_GNUC_PRINTF(2, 0)
static void vreport(report_type type, const char *fmt, va_list ap)
{
+ Monitor *cur = monitor_cur();
gchar *timestr;
- if (message_with_timestamp && !monitor_cur()) {
+ if (message_with_timestamp && !cur) {
timestr = real_time_iso8601();
- error_printf("%s ", timestr);
+ fprintf(stderr, "%s ", timestr);
g_free(timestr);
}
/* Only prepend guest name if -msg guest-name and -name guest=... are set */
- if (error_with_guestname && error_guest_name && !monitor_cur()) {
- error_printf("%s ", error_guest_name);
+ if (error_with_guestname && error_guest_name && !cur) {
+ fprintf(stderr, "%s ", error_guest_name);
}
- print_loc();
+ print_loc(cur);
switch (type) {
case REPORT_TYPE_ERROR:
break;
case REPORT_TYPE_WARNING:
- error_printf("warning: ");
+ error_printf_mon(cur, "warning: ");
break;
case REPORT_TYPE_INFO:
- error_printf("info: ");
+ error_printf_mon(cur, "info: ");
break;
}
- error_vprintf(fmt, ap);
- error_printf("\n");
+ error_vprintf_mon(cur, fmt, ap);
+ error_printf_mon(cur, "\n");
}
/*
--
2.53.0