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[RFC 1/3] hmp: avoid the nested event loop in handle_hmp_command()
From: |
Stefan Hajnoczi |
Subject: |
[RFC 1/3] hmp: avoid the nested event loop in handle_hmp_command() |
Date: |
Wed, 6 Sep 2023 15:01:39 -0400 |
Coroutine HMP commands currently run to completion in a nested event
loop with the Big QEMU Lock (BQL) held. The call_rcu thread also uses
the BQL and cannot process work while the coroutine monitor command is
running. A deadlock occurs when monitor commands attempt to wait for
call_rcu work to finish.
This patch refactors the HMP monitor to use the existing event loop
instead of creating a nested event loop. This will allow the next
patches to rely on draining call_rcu work.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
monitor/hmp.c | 28 +++++++++++++++-------------
1 file changed, 15 insertions(+), 13 deletions(-)
diff --git a/monitor/hmp.c b/monitor/hmp.c
index 69c1b7e98a..6cff2810aa 100644
--- a/monitor/hmp.c
+++ b/monitor/hmp.c
@@ -1111,15 +1111,17 @@ typedef struct HandleHmpCommandCo {
Monitor *mon;
const HMPCommand *cmd;
QDict *qdict;
- bool done;
} HandleHmpCommandCo;
-static void handle_hmp_command_co(void *opaque)
+static void coroutine_fn handle_hmp_command_co(void *opaque)
{
HandleHmpCommandCo *data = opaque;
+
handle_hmp_command_exec(data->mon, data->cmd, data->qdict);
monitor_set_cur(qemu_coroutine_self(), NULL);
- data->done = true;
+ qobject_unref(data->qdict);
+ monitor_resume(data->mon);
+ g_free(data);
}
void handle_hmp_command(MonitorHMP *mon, const char *cmdline)
@@ -1157,20 +1159,20 @@ void handle_hmp_command(MonitorHMP *mon, const char
*cmdline)
Monitor *old_mon = monitor_set_cur(qemu_coroutine_self(),
&mon->common);
handle_hmp_command_exec(&mon->common, cmd, qdict);
monitor_set_cur(qemu_coroutine_self(), old_mon);
+ qobject_unref(qdict);
} else {
- HandleHmpCommandCo data = {
- .mon = &mon->common,
- .cmd = cmd,
- .qdict = qdict,
- .done = false,
- };
- Coroutine *co = qemu_coroutine_create(handle_hmp_command_co, &data);
+ HandleHmpCommandCo *data; /* freed by handle_hmp_command_co() */
+
+ data = g_new(HandleHmpCommandCo, 1);
+ data->mon = &mon->common;
+ data->cmd = cmd;
+ data->qdict = qdict; /* freed by handle_hmp_command_co() */
+
+ Coroutine *co = qemu_coroutine_create(handle_hmp_command_co, data);
+ monitor_suspend(&mon->common); /* resumed by handle_hmp_command_co() */
monitor_set_cur(co, &mon->common);
aio_co_enter(qemu_get_aio_context(), co);
- AIO_WAIT_WHILE_UNLOCKED(NULL, !data.done);
}
-
- qobject_unref(qdict);
}
static void cmd_completion(MonitorHMP *mon, const char *name, const char *list)
--
2.41.0
- [RFC 0/3] qmp: make qmp_device_add() a coroutine, Stefan Hajnoczi, 2023/09/06
- [RFC 1/3] hmp: avoid the nested event loop in handle_hmp_command(),
Stefan Hajnoczi <=
- Re: [RFC 1/3] hmp: avoid the nested event loop in handle_hmp_command(), Dr. David Alan Gilbert, 2023/09/06
- Re: [RFC 1/3] hmp: avoid the nested event loop in handle_hmp_command(), Stefan Hajnoczi, 2023/09/07
- Re: [RFC 1/3] hmp: avoid the nested event loop in handle_hmp_command(), Dr. David Alan Gilbert, 2023/09/07
- Re: [RFC 1/3] hmp: avoid the nested event loop in handle_hmp_command(), Stefan Hajnoczi, 2023/09/07
- Re: [RFC 1/3] hmp: avoid the nested event loop in handle_hmp_command(), Dr. David Alan Gilbert, 2023/09/07
- Re: [RFC 1/3] hmp: avoid the nested event loop in handle_hmp_command(), Stefan Hajnoczi, 2023/09/07
[RFC 3/3] qmp: make qmp_device_add() a coroutine, Stefan Hajnoczi, 2023/09/06
[RFC 2/3] rcu: add drain_call_rcu_co() API, Stefan Hajnoczi, 2023/09/06