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_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 a decision about whether output will go to monitor_[v]printf()
or fprintf() must be made upfront, and then those functions called
directly.
$ 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
This change requires adding a stub for monitor_printf() since that
is now called directly by vreport(), where monitor_vprintf() was
only needed previously.
Signed-off-by: Daniel P. Berrangé <berra...@redhat.com>
---
stubs/monitor-core.c | 5 +++
tests/unit/test-util-sockets.c | 1 +
util/error-report.c | 60 ++++++++++++++++++++++++----------
3 files changed, 48 insertions(+), 18 deletions(-)
diff --git a/stubs/monitor-core.c b/stubs/monitor-core.c
index 1e0b11ec29..70b1f7a994 100644
--- a/stubs/monitor-core.c
+++ b/stubs/monitor-core.c
@@ -30,3 +30,8 @@ int monitor_vprintf(Monitor *mon, const char *fmt, va_list ap)
{
abort();
}
+
+int monitor_printf(Monitor *mon, const char *fmt, ...)
+{
+ abort();
+}
diff --git a/tests/unit/test-util-sockets.c b/tests/unit/test-util-sockets.c
index d40813c682..53733163dd 100644
--- a/tests/unit/test-util-sockets.c
+++ b/tests/unit/test-util-sockets.c
@@ -76,6 +76,7 @@ Monitor *monitor_cur_hmp(void) { return cur_mon; }
bool monitor_cur_is_qmp(void) { return false; }
Monitor *monitor_set_cur(Coroutine *co, Monitor *mon) { abort(); }
int monitor_vprintf(Monitor *mon, const char *fmt, va_list ap) { abort(); }
+int monitor_printf(Monitor *mon, const char *fmt, ...) { abort(); }
#ifndef _WIN32
static void test_socket_fd_pass_name_good(void)
diff --git a/util/error-report.c b/util/error-report.c
index c0fcf388de..6c887047e3 100644
--- a/util/error-report.c
+++ b/util/error-report.c
@@ -29,6 +29,9 @@ bool message_with_timestamp;
bool error_with_guestname;
const char *error_guest_name;
+typedef void (*error_print_func)(void *opaque, const char *fmt, ...);
+typedef void (*error_print_vfunc)(void *opaque, const char *fmt, va_list ap);
+
/*
* Print to current monitor if we have one, else to stderr.
*/
@@ -151,34 +154,34 @@ 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(bool cur, error_print_func print_func, void
*print_opaque)
{
const char *sep = "";
int i;
const char *const *argp;
- if (!monitor_cur_hmp() && g_get_prgname()) {
- error_printf("%s:", g_get_prgname());
+ if (!cur && g_get_prgname()) {
+ print_func(print_opaque, "%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]);
+ print_func(print_opaque, "%s%s", sep, argp[i]);
sep = " ";
}
- error_printf(": ");
+ print_func(print_opaque, ": ");
break;
case LOC_FILE:
- error_printf("%s:", (const char *)cur_loc->ptr);
+ print_func(print_opaque, "%s:", (const char *)cur_loc->ptr);
if (cur_loc->num) {
- error_printf("%d:", cur_loc->num);
+ print_func(print_opaque, "%d:", cur_loc->num);
}
- error_printf(" ");
+ print_func(print_opaque, " ");
break;
default:
- error_printf("%s", sep);
+ print_func(print_opaque, "%s", sep);
}
}
@@ -199,34 +202,55 @@ real_time_iso8601(void)
G_GNUC_PRINTF(2, 0)
static void vreport(report_type type, const char *fmt, va_list ap)
{
+ /*
+ * Calling monitor_cur_hmp() will acquire/release mutexes,
+ * which triggers trace probes, which can trigger
+ * qemu_log calls, which would interleave with output
+ * from this. Hence cache the monitor handle upfront
+ * so any tracing appears before we start outputting.
+ */
+ Monitor *cur = monitor_cur_hmp();
+ error_print_func print_func;
+ error_print_vfunc print_vfunc;
+ void *print_opaque;
gchar *timestr;
- if (message_with_timestamp && !monitor_cur_hmp()) {
+ if (cur) {
+ print_func = (error_print_func)monitor_printf;
+ print_vfunc = (error_print_vfunc)monitor_vprintf;
+ print_opaque = cur;
+ } else {
+ print_func = (error_print_func)fprintf;
+ print_vfunc = (error_print_vfunc)vfprintf;
+ print_opaque = stderr;
+ }
+
+ if (message_with_timestamp && !cur) {
timestr = real_time_iso8601();
- error_printf("%s ", timestr);
+ print_func(print_opaque, "%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_hmp()) {
- error_printf("%s ", error_guest_name);
+ if (error_with_guestname && error_guest_name && !cur) {
+ print_func(print_opaque, "%s ", error_guest_name);
}
- print_loc();
+ print_loc(!!cur, print_func, print_opaque);
switch (type) {
case REPORT_TYPE_ERROR:
break;
case REPORT_TYPE_WARNING:
- error_printf("warning: ");
+ print_func(print_opaque, "warning: ");
break;
case REPORT_TYPE_INFO:
- error_printf("info: ");
+ print_func(print_opaque, "info: ");
break;
}
- error_vprintf(fmt, ap);
- error_printf("\n");
+ print_vfunc(print_opaque, fmt, ap);
+ print_func(print_opaque, "\n");
}
/*
