From e69ee454b5f9dff3af48bcfc3d9691b3edb02fe2 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Mon, 5 Oct 2020 17:58:48 +0200 Subject: [PATCH] monitor: Make current monitor a per-coroutine property This way, a monitor command handler will still be able to access the current monitor, but when it yields, all other code code will correctly get NULL from monitor_cur(). This uses a hash table to map the coroutine pointer to the current monitor of that coroutine. Outside of coroutine context, we associate the current monitor with the leader coroutine of the current thread. Approaches to implement some form of coroutine local storage directly in the coroutine core code have been considered and discarded because they didn't end up being much more generic than the hash table and their performance impact on coroutines not using coroutine local storage was unclear. As the block layer uses a coroutine per I/O request, this is a fast path and we have to be careful. It's safest to just stay out of this path with code only used by the monitor. Signed-off-by: Kevin Wolf Reviewed-by: Eric Blake Message-Id: <20201005155855.256490-8-kwolf@redhat.com> Reviewed-by: Markus Armbruster Reviewed-by: Stefan Hajnoczi Signed-off-by: Markus Armbruster --- include/monitor/monitor.h | 2 +- monitor/hmp.c | 4 ++-- monitor/monitor.c | 34 +++++++++++++++++++++++++++------- qapi/qmp-dispatch.c | 4 ++-- stubs/monitor-core.c | 2 +- 5 files changed, 33 insertions(+), 13 deletions(-) diff --git a/include/monitor/monitor.h b/include/monitor/monitor.h index 543eafcb76..348bfad3d5 100644 --- a/include/monitor/monitor.h +++ b/include/monitor/monitor.h @@ -13,7 +13,7 @@ typedef struct MonitorOptions MonitorOptions; extern QemuOptsList qemu_mon_opts; Monitor *monitor_cur(void); -Monitor *monitor_set_cur(Monitor *mon); +Monitor *monitor_set_cur(Coroutine *co, Monitor *mon); bool monitor_cur_is_qmp(void); void monitor_init_globals(void); diff --git a/monitor/hmp.c b/monitor/hmp.c index 560ec98e7b..abaf939b2d 100644 --- a/monitor/hmp.c +++ b/monitor/hmp.c @@ -1081,9 +1081,9 @@ void handle_hmp_command(MonitorHMP *mon, const char *cmdline) } /* old_mon is non-NULL when called from qmp_human_monitor_command() */ - old_mon = monitor_set_cur(&mon->common); + old_mon = monitor_set_cur(qemu_coroutine_self(), &mon->common); cmd->cmd(&mon->common, qdict); - monitor_set_cur(old_mon); + monitor_set_cur(qemu_coroutine_self(), old_mon); qobject_unref(qdict); } diff --git a/monitor/monitor.c b/monitor/monitor.c index 099c164c6d..ef68ca9d21 100644 --- a/monitor/monitor.c +++ b/monitor/monitor.c @@ -58,29 +58,48 @@ IOThread *mon_iothread; /* Bottom half to dispatch the requests received from I/O thread */ QEMUBH *qmp_dispatcher_bh; -/* Protects mon_list, monitor_qapi_event_state, monitor_destroyed. */ +/* + * Protects mon_list, monitor_qapi_event_state, coroutine_mon, + * monitor_destroyed. + */ QemuMutex monitor_lock; static GHashTable *monitor_qapi_event_state; +static GHashTable *coroutine_mon; /* Maps Coroutine* to Monitor* */ MonitorList mon_list; int mon_refcount; static bool monitor_destroyed; -static __thread Monitor *cur_monitor; - Monitor *monitor_cur(void) { - return cur_monitor; + Monitor *mon; + + qemu_mutex_lock(&monitor_lock); + mon = g_hash_table_lookup(coroutine_mon, qemu_coroutine_self()); + qemu_mutex_unlock(&monitor_lock); + + return mon; } /** * Sets a new current monitor and returns the old one. + * + * If a non-NULL monitor is set for a coroutine, another call + * resetting it to NULL is required before the coroutine terminates, + * otherwise a stale entry would remain in the hash table. */ -Monitor *monitor_set_cur(Monitor *mon) +Monitor *monitor_set_cur(Coroutine *co, Monitor *mon) { - Monitor *old_monitor = cur_monitor; + Monitor *old_monitor = monitor_cur(); + + qemu_mutex_lock(&monitor_lock); + if (mon) { + g_hash_table_replace(coroutine_mon, co, mon); + } else { + g_hash_table_remove(coroutine_mon, co); + } + qemu_mutex_unlock(&monitor_lock); - cur_monitor = mon; return old_monitor; } @@ -623,6 +642,7 @@ void monitor_init_globals_core(void) { monitor_qapi_event_init(); qemu_mutex_init(&monitor_lock); + coroutine_mon = g_hash_table_new(NULL, NULL); /* * The dispatcher BH must run in the main loop thread, since we diff --git a/qapi/qmp-dispatch.c b/qapi/qmp-dispatch.c index 2fdbc0fba4..5677ba92ca 100644 --- a/qapi/qmp-dispatch.c +++ b/qapi/qmp-dispatch.c @@ -154,11 +154,11 @@ QDict *qmp_dispatch(const QmpCommandList *cmds, QObject *request, } assert(monitor_cur() == NULL); - monitor_set_cur(cur_mon); + monitor_set_cur(qemu_coroutine_self(), cur_mon); cmd->fn(args, &ret, &err); - monitor_set_cur(NULL); + monitor_set_cur(qemu_coroutine_self(), NULL); qobject_unref(args); if (err) { /* or assert(!ret) after reviewing all handlers: */ diff --git a/stubs/monitor-core.c b/stubs/monitor-core.c index dc1748bf13..d058a2a00d 100644 --- a/stubs/monitor-core.c +++ b/stubs/monitor-core.c @@ -8,7 +8,7 @@ Monitor *monitor_cur(void) return NULL; } -Monitor *monitor_set_cur(Monitor *mon) +Monitor *monitor_set_cur(Coroutine *co, Monitor *mon) { return NULL; }