We've been up until now cleaning up any file descriptors that have
been passed into QEMU and never duplicated[1,2]. A file descriptor
without duplicates indicates that no part of QEMU has made use of
it. This approach is starting to show some cracks now that we're
starting to consume fds from the migration code:
- Doing cleanup every time the last monitor connection closes works to
reap unused fds, but also has the side effect of forcing the
management layer to pass the file descriptors again in case of a
disconnect/re-connect, if that happened to be the only monitor
connection.
Another side effect is that removing an fd with qmp_remove_fd() is
effectively delayed until the last monitor connection closes.
The reliance on mon_refcount is also problematic because it's racy.
- Checking runstate_is_running() skips the cleanup unless the VM is
running and avoids premature cleanup of the fds, but also has the
side effect of blocking the legitimate removal of an fd via
qmp_remove_fd() if the VM happens to be in another state.
This affects qmp_remove_fd() and qmp_query_fdsets() in particular
because requesting a removal at a bad time (guest stopped) might
cause an fd to never be removed, or to be removed at a much later
point in time, causing the query command to continue showing the
supposedly removed fd/fdset.
Note that file descriptors that *have* been duplicated are owned by
the code that uses them and will be removed after qemu_close() is
called. Therefore we've decided that the best course of action to
avoid the undesired side-effects is to stop managing non-duplicated
file descriptors.
1- efb87c1697 ("monitor: Clean up fd sets on monitor disconnect")
2- ebe52b592d ("monitor: Prevent removing fd from set during init")
Signed-off-by: Fabiano Rosas <faro...@suse.de>
---
monitor/fds.c | 15 ++++++++-------
monitor/hmp.c | 2 --
monitor/monitor-internal.h | 1 -
monitor/qmp.c | 2 --
4 files changed, 8 insertions(+), 12 deletions(-)
diff --git a/monitor/fds.c b/monitor/fds.c
index 101e21720d..f7b98814fa 100644
--- a/monitor/fds.c
+++ b/monitor/fds.c
@@ -169,6 +169,11 @@ int monitor_get_fd(Monitor *mon, const char *fdname, Error
**errp)
static void monitor_fdset_free(MonFdset *mon_fdset)
{
+ /*
+ * Only remove an empty fdset. The fds are owned by the user and
+ * should have been removed with qmp_remove_fd(). The dup_fds are
+ * owned by QEMU and should have been removed with qemu_close().
+ */
if (QLIST_EMPTY(&mon_fdset->fds) && QLIST_EMPTY(&mon_fdset->dup_fds)) {
QLIST_REMOVE(mon_fdset, next);
g_free(mon_fdset);
@@ -189,9 +194,7 @@ static void monitor_fdset_cleanup(MonFdset *mon_fdset)
MonFdsetFd *mon_fdset_fd_next;
QLIST_FOREACH_SAFE(mon_fdset_fd, &mon_fdset->fds, next, mon_fdset_fd_next)
{
- if ((mon_fdset_fd->removed ||
- (QLIST_EMPTY(&mon_fdset->dup_fds) && mon_refcount == 0)) &&
- runstate_is_running()) {
+ if (mon_fdset_fd->removed) {
monitor_fdset_fd_free(mon_fdset_fd);
}
}
@@ -206,7 +209,7 @@ void monitor_fdsets_cleanup(void)
QEMU_LOCK_GUARD(&mon_fdsets_lock);
QLIST_FOREACH_SAFE(mon_fdset, &mon_fdsets, next, mon_fdset_next) {
- monitor_fdset_cleanup(mon_fdset);
+ monitor_fdset_free(mon_fdset);
}
}
@@ -479,9 +482,7 @@ void monitor_fdset_dup_fd_remove(int dup_fd)
if (mon_fdset_fd_dup->fd == dup_fd) {
QLIST_REMOVE(mon_fdset_fd_dup, next);
g_free(mon_fdset_fd_dup);
- if (QLIST_EMPTY(&mon_fdset->dup_fds)) {
- monitor_fdset_cleanup(mon_fdset);
- }
+ monitor_fdset_free(mon_fdset);
return;
}
}
diff --git a/monitor/hmp.c b/monitor/hmp.c
index 69c1b7e98a..460e8832f6 100644
--- a/monitor/hmp.c
+++ b/monitor/hmp.c
@@ -1437,11 +1437,9 @@ static void monitor_event(void *opaque, QEMUChrEvent
event)
monitor_resume(mon);
}
qemu_mutex_unlock(&mon->mon_lock);
- mon_refcount++;
break;
case CHR_EVENT_CLOSED:
- mon_refcount--;
monitor_fdsets_cleanup();
break;
diff --git a/monitor/monitor-internal.h b/monitor/monitor-internal.h
index 252de85681..cb628f681d 100644
--- a/monitor/monitor-internal.h
+++ b/monitor/monitor-internal.h
@@ -168,7 +168,6 @@ extern bool qmp_dispatcher_co_shutdown;
extern QmpCommandList qmp_commands, qmp_cap_negotiation_commands;
extern QemuMutex monitor_lock;
extern MonitorList mon_list;
-extern int mon_refcount;
extern HMPCommand hmp_cmds[];
diff --git a/monitor/qmp.c b/monitor/qmp.c
index a239945e8d..5e538f34c0 100644
--- a/monitor/qmp.c
+++ b/monitor/qmp.c
@@ -466,7 +466,6 @@ static void monitor_qmp_event(void *opaque, QEMUChrEvent
event)
data = qmp_greeting(mon);
qmp_send_response(mon, data);
qobject_unref(data);
- mon_refcount++;
break;
case CHR_EVENT_CLOSED:
/*
@@ -479,7 +478,6 @@ static void monitor_qmp_event(void *opaque, QEMUChrEvent
event)
json_message_parser_destroy(&mon->parser);
json_message_parser_init(&mon->parser, handle_qmp_command,
mon, NULL);
- mon_refcount--;
monitor_fdsets_cleanup();
break;
case CHR_EVENT_BREAK:
--
2.35.3
