From: Maxim Levitsky <mlevitsk@redhat.com>
To: Markus Armbruster <armbru@redhat.com>
Cc: "Fam Zheng" <fam@euphon.net>,
"Daniel P.Berrangé" <berrange@redhat.com>,
"Eduardo Habkost" <ehabkost@redhat.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
qemu-devel@nongnu.org, "Paolo Bonzini" <pbonzini@redhat.com>
Subject: Re: [PATCH v2 2/7] Implement drain_call_rcu and use it in hmp_device_del
Date: Thu, 09 Jul 2020 14:56:41 +0300 [thread overview]
Message-ID: <36fae287a2b5e06c35facf22e5d9c16fbbf9908e.camel@redhat.com> (raw)
In-Reply-To: <87wo3csyn4.fsf@dusky.pond.sub.org>
On Thu, 2020-07-09 at 13:42 +0200, Markus Armbruster wrote:
> Maxim Levitsky <mlevitsk@redhat.com> writes:
>
> > This allows to preserve the semantics of hmp_device_del,
> > that the device is deleted immediatly which was changed by previos
> > patch that delayed this to RCU callback
> >
> > Suggested-by: Stefan Hajnoczi <stefanha@gmail.com>
> > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> > ---
> > include/qemu/rcu.h | 1 +
> > qdev-monitor.c | 3 +++
> > util/rcu.c | 33 +++++++++++++++++++++++++++++++++
> > 3 files changed, 37 insertions(+)
> >
> > diff --git a/include/qemu/rcu.h b/include/qemu/rcu.h
> > index 570aa603eb..0e375ebe13 100644
> > --- a/include/qemu/rcu.h
> > +++ b/include/qemu/rcu.h
> > @@ -133,6 +133,7 @@ struct rcu_head {
> > };
> >
> > extern void call_rcu1(struct rcu_head *head, RCUCBFunc *func);
> > +extern void drain_call_rcu(void);
> >
> > /* The operands of the minus operator must have the same type,
> > * which must be the one that we specify in the cast.
> > diff --git a/qdev-monitor.c b/qdev-monitor.c
> > index 56cee1483f..70877840a2 100644
> > --- a/qdev-monitor.c
> > +++ b/qdev-monitor.c
> > @@ -812,6 +812,8 @@ void qmp_device_add(QDict *qdict, QObject **ret_data, Error **errp)
> > return;
> > }
> > dev = qdev_device_add(opts, &local_err);
> > + drain_call_rcu();
> > +
> > if (!dev) {
> > error_propagate(errp, local_err);
> > qemu_opts_del(opts);
> > @@ -904,6 +906,7 @@ void qmp_device_del(const char *id, Error **errp)
> > }
> >
> > qdev_unplug(dev, errp);
> > + drain_call_rcu();
> > }
> > }
> >
>
> Subject claims "in hmp_device_del", code has it in qmp_device_add() and
> qmp_device_del(). Please advise.
I added it in both, because addition of a device can fail and trigger removal,
which can also be now delayed due to RCU.
Since both device_add and device_del aren't used often, the overhead won't
be a problem IMHO.
Best regards,
Maxim Levitsky
>
> [...]
next prev parent reply other threads:[~2020-07-09 11:57 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-11 16:09 [PATCH v2 0/7] RFC/WIP: Fix scsi devices plug/unplug races w.r.t virtio-scsi iothread Maxim Levitsky
2020-05-11 16:09 ` [PATCH v2 1/7] scsi/scsi_bus: switch search direction in scsi_device_find Maxim Levitsky
2020-05-27 12:53 ` Stefan Hajnoczi
2020-05-11 16:09 ` [PATCH v2 2/7] Implement drain_call_rcu and use it in hmp_device_del Maxim Levitsky
2020-05-27 13:11 ` Stefan Hajnoczi
2020-07-09 9:34 ` Maxim Levitsky
2020-07-09 11:42 ` Markus Armbruster
2020-07-09 11:56 ` Maxim Levitsky [this message]
2020-07-09 12:02 ` Paolo Bonzini
2020-05-11 16:09 ` [PATCH v2 3/7] device-core: use RCU for list of childs of a bus Maxim Levitsky
2020-05-27 14:45 ` Stefan Hajnoczi
2020-07-09 9:40 ` Maxim Levitsky
2020-05-11 16:09 ` [PATCH v2 4/7] device-core: use atomic_set on .realized property Maxim Levitsky
2020-05-27 15:00 ` Stefan Hajnoczi
2020-07-09 10:24 ` Maxim Levitsky
2020-05-11 16:09 ` [PATCH v2 5/7] virtio-scsi: don't touch scsi devices that are not yet realized or about to be un-realized Maxim Levitsky
2020-05-27 15:08 ` Stefan Hajnoczi
2020-05-11 16:09 ` [PATCH v2 6/7] scsi: Add scsi_device_get Maxim Levitsky
2020-05-27 15:27 ` Stefan Hajnoczi
2020-07-09 10:35 ` Maxim Levitsky
2020-05-11 16:09 ` [PATCH v2 7/7] virtio-scsi: use scsi_device_get Maxim Levitsky
2020-05-27 15:50 ` Stefan Hajnoczi
2020-07-09 10:43 ` Maxim Levitsky
2020-05-27 15:50 ` Stefan Hajnoczi
2020-05-11 18:03 ` [PATCH v2 0/7] RFC/WIP: Fix scsi devices plug/unplug races w.r.t virtio-scsi iothread no-reply
2020-05-11 18:03 ` no-reply
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