The first thread to issue a client RPC request will own the event
loop execution, sitting in the virNetClientIOEventLoop function.
It releases the client lock while running:
virNetClientUnlock()
g_main_loop_run()
virNetClientLock()
If a second thread arrives with an RPC request, it will queue it
for the first thread to process. To inform the first thread that
there's a new request it calls g_main_loop_quit() to break it out
of the main loop.
This works if the first thread is in g_main_loop_run() at that
time. There is a small window of opportunity, however, where
the first thread has released the client lock, but not yet got
into g_main_loop_run(). If that happens, the wakeup from the
second thread is lost.
This patch deals with that by changing the way the wakeup is
performed. Instead of directly calling g_main_loop_quit(), the
second thread creates an idle source to run the quit function
from within the first thread. This guarantees that the first
thread will see the wakeup.
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
src/rpc/virnetclient.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/src/rpc/virnetclient.c b/src/rpc/virnetclient.c
index 4ab8af68c5..68098b1c8d 100644
--- a/src/rpc/virnetclient.c
+++ b/src/rpc/virnetclient.c
@@ -1848,6 +1848,15 @@ static void virNetClientIOUpdateCallback(virNetClient *client,
}
+static gboolean virNetClientIOWakeup(gpointer opaque)
+{
+ GMainLoop *loop = opaque;
+
+ g_main_loop_quit(loop);
+
+ return G_SOURCE_REMOVE;
+}
+
/*
* This function sends a message to remote server and awaits a reply
*
@@ -1925,7 +1934,9 @@ static int virNetClientIO(virNetClient *client,
/* Check to see if another thread is dispatching */
if (client->haveTheBuck) {
/* Force other thread to wakeup from poll */
- g_main_loop_quit(client->eventLoop);
+ GSource *wakeup = g_idle_source_new();
+ g_source_set_callback(wakeup, virNetClientIOWakeup, client->eventLoop, NULL);
+ g_source_attach(wakeup, client->eventCtx);
/* If we are non-blocking, detach the thread and keep the call in the
* queue. */
--
2.43.0
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On 12/18/23 13:23, Daniel P. Berrangé wrote: > The first thread to issue a client RPC request will own the event > loop execution, sitting in the virNetClientIOEventLoop function. > > It releases the client lock while running: > > virNetClientUnlock() > g_main_loop_run() > virNetClientLock() > > If a second thread arrives with an RPC request, it will queue it > for the first thread to process. To inform the first thread that > there's a new request it calls g_main_loop_quit() to break it out > of the main loop. > > This works if the first thread is in g_main_loop_run() at that > time. There is a small window of opportunity, however, where > the first thread has released the client lock, but not yet got > into g_main_loop_run(). If that happens, the wakeup from the > second thread is lost. > > This patch deals with that by changing the way the wakeup is > performed. Instead of directly calling g_main_loop_quit(), the > second thread creates an idle source to run the quit function > from within the first thread. This guarantees that the first > thread will see the wakeup. > > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> > --- > > src/rpc/virnetclient.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff --git a/src/rpc/virnetclient.c b/src/rpc/virnetclient.c > index 4ab8af68c5..68098b1c8d 100644 > --- a/src/rpc/virnetclient.c > +++ b/src/rpc/virnetclient.c > @@ -1848,6 +1848,15 @@ static void virNetClientIOUpdateCallback(virNetClient *client, > } > > > +static gboolean virNetClientIOWakeup(gpointer opaque) > +{ > + GMainLoop *loop = opaque; > + > + g_main_loop_quit(loop); > + > + return G_SOURCE_REMOVE; > +} > + > /* > * This function sends a message to remote server and awaits a reply > * > @@ -1925,7 +1934,9 @@ static int virNetClientIO(virNetClient *client, > /* Check to see if another thread is dispatching */ > if (client->haveTheBuck) { > /* Force other thread to wakeup from poll */ > - g_main_loop_quit(client->eventLoop); > + GSource *wakeup = g_idle_source_new(); > + g_source_set_callback(wakeup, virNetClientIOWakeup, client->eventLoop, NULL); > + g_source_attach(wakeup, client->eventCtx); > > /* If we are non-blocking, detach the thread and keep the call in the > * queue. */ Reviewed-by: Denis V. Lunev <den@openvz.org> _______________________________________________ Devel mailing list -- devel@lists.libvirt.org To unsubscribe send an email to devel-leave@lists.libvirt.org
Hello, Your patch works on our stand without any freezing. Tested by: Fima Shevrin <efim.shevrin@virtuozzo.com> ________________________________ From: Daniel P. Berrangé <berrange@redhat.com> Sent: Monday, December 18, 2023 20:23 To: devel@lists.libvirt.org <devel@lists.libvirt.org> Cc: Efim Shevrin <efim.shevrin@virtuozzo.com>; Denis V. Lunev <den@openvz.org>; Daniel P. Berrangé <berrange@redhat.com> Subject: [PATCH] rpc: fix race in waking up client event loop [You don't often get email from berrange@redhat.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ] The first thread to issue a client RPC request will own the event loop execution, sitting in the virNetClientIOEventLoop function. It releases the client lock while running: virNetClientUnlock() g_main_loop_run() virNetClientLock() If a second thread arrives with an RPC request, it will queue it for the first thread to process. To inform the first thread that there's a new request it calls g_main_loop_quit() to break it out of the main loop. This works if the first thread is in g_main_loop_run() at that time. There is a small window of opportunity, however, where the first thread has released the client lock, but not yet got into g_main_loop_run(). If that happens, the wakeup from the second thread is lost. This patch deals with that by changing the way the wakeup is performed. Instead of directly calling g_main_loop_quit(), the second thread creates an idle source to run the quit function from within the first thread. This guarantees that the first thread will see the wakeup. Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> --- src/rpc/virnetclient.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/src/rpc/virnetclient.c b/src/rpc/virnetclient.c index 4ab8af68c5..68098b1c8d 100644 --- a/src/rpc/virnetclient.c +++ b/src/rpc/virnetclient.c @@ -1848,6 +1848,15 @@ static void virNetClientIOUpdateCallback(virNetClient *client, } +static gboolean virNetClientIOWakeup(gpointer opaque) +{ + GMainLoop *loop = opaque; + + g_main_loop_quit(loop); + + return G_SOURCE_REMOVE; +} + /* * This function sends a message to remote server and awaits a reply * @@ -1925,7 +1934,9 @@ static int virNetClientIO(virNetClient *client, /* Check to see if another thread is dispatching */ if (client->haveTheBuck) { /* Force other thread to wakeup from poll */ - g_main_loop_quit(client->eventLoop); + GSource *wakeup = g_idle_source_new(); + g_source_set_callback(wakeup, virNetClientIOWakeup, client->eventLoop, NULL); + g_source_attach(wakeup, client->eventCtx); /* If we are non-blocking, detach the thread and keep the call in the * queue. */ -- 2.43.0 _______________________________________________ Devel mailing list -- devel@lists.libvirt.org To unsubscribe send an email to devel-leave@lists.libvirt.org
On 12/18/23 13:23, Daniel P. Berrangé wrote: > The first thread to issue a client RPC request will own the event > loop execution, sitting in the virNetClientIOEventLoop function. > > It releases the client lock while running: > > virNetClientUnlock() > g_main_loop_run() > virNetClientLock() > > If a second thread arrives with an RPC request, it will queue it > for the first thread to process. To inform the first thread that > there's a new request it calls g_main_loop_quit() to break it out > of the main loop. > > This works if the first thread is in g_main_loop_run() at that > time. There is a small window of opportunity, however, where > the first thread has released the client lock, but not yet got > into g_main_loop_run(). If that happens, the wakeup from the > second thread is lost. > > This patch deals with that by changing the way the wakeup is > performed. Instead of directly calling g_main_loop_quit(), the > second thread creates an idle source to run the quit function > from within the first thread. This guarantees that the first > thread will see the wakeup. > > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> > --- > > src/rpc/virnetclient.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > Reviewed-by: Michal Privoznik <mprivozn@redhat.com> Michal _______________________________________________ Devel mailing list -- devel@lists.libvirt.org To unsubscribe send an email to devel-leave@lists.libvirt.org
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