Daniel P. Berrangé <[email protected]> writes:
> 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 <[email protected]>
> Signed-off-by: Daniel P. Berrangé <[email protected]>
> ---
> 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.
This is now misleading. Let's use
* Print to @cur_mon if non-null, 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.
Likewise.
> + */
> +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;
> +}
> +
Keep its function comment, i.e.
/*
* Print to the current human monitor if we have one, else to stderr.
*/
> +int error_vprintf(const char *fmt, va_list ap)
> +{
> + return error_vprintf_mon(monitor_cur(), fmt, ap);
> +}
> +
This one lost its function comment in commit 397d30e9401. Let's correct
that accident:
/*
* Print to the current human monitor if we have one, else to stderr.
*/
> 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;
> }
With these trivial touch-ups
Reviewed-by: Markus Armbruster <[email protected]>
[...]
