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 c7f70bd95b..f666ca4149 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); } } @@ -203,34 +223,35 @@ char *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