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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1772627353; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=uUO9apoCTG6e/J+8/LyzATgtyfuwsHJ40yHagC1ufac=; b=ZtsHOhQHOT/XGtniN/dCJtE1qf/nucARfGyMLwL6f5nCR033amNCIbx7nHIYfMRmVDn8eS MqJa/NbFF2KVi6R2eDlFAnrHc5bxLK896DUSUTsRD+muTtpH3xzM7GBoAnmz8ETsC/tDeI +3Lqn+/EHRq8a46IGzjvwjSJy41JvH0= X-MC-Unique: El0SvASCNzaITr0Js0zjBQ-1 X-Mimecast-MFC-AGG-ID: El0SvASCNzaITr0Js0zjBQ_1772627350 From: Kevin Wolf To: qemu-block@nongnu.org Cc: kwolf@redhat.com, hreitz@redhat.com, xeor@yandex-team.ru, vsementsov@yandex-team.ru, pkrempa@redhat.com, qemu-devel@nongnu.org, qemu-stable@nongnu.org Subject: [PATCH v2] block: Never drop BLOCK_IO_ERROR with action=stop for rate limiting Date: Wed, 4 Mar 2026 13:28:00 +0100 Message-ID: <20260304122800.51923-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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charset="utf-8" Commit 2155d2dd introduced rate limiting for BLOCK_IO_ERROR to emit an event only once a second. This makes sense for cases in which the guest keeps running and can submit more requests that would possibly also fail because there is a problem with the backend. However, if the error policy is configured so that the VM is stopped on errors, this is both unnecessary because stopping the VM means that the guest can't issue more requests and in fact harmful because stopping the VM is an important state change that management tools need to keep track of even if it happens more than once in a given second. If an event is dropped, the management tool would see a VM randomly going to paused state without an associated error, so it has a hard time deciding how to handle the situation. This patch disables rate limiting for action=3Dstop by not relying on the event type alone any more in monitor_qapi_event_queue_no_reenter(), but checking action for BLOCK_IO_ERROR, too. If the error is reported to the guest or ignored, the rate limiting stays in place. Fixes: 2155d2dd7f73 ('block-backend: per-device throttling of BLOCK_IO_ERRO= R reports') Signed-off-by: Kevin Wolf --- qapi/block-core.json | 2 +- monitor/monitor.c | 21 ++++++++++++++++++++- 2 files changed, 21 insertions(+), 2 deletions(-) diff --git a/qapi/block-core.json b/qapi/block-core.json index b66bf316e2f..da0b36a3751 100644 --- a/qapi/block-core.json +++ b/qapi/block-core.json @@ -5794,7 +5794,7 @@ # .. note:: If action is "stop", a `STOP` event will eventually follow # the `BLOCK_IO_ERROR` event. # -# .. note:: This event is rate-limited. +# .. note:: This event is rate-limited, except if action is "stop". # # Since: 0.13 # diff --git a/monitor/monitor.c b/monitor/monitor.c index 1273eb72605..37fa674cfe6 100644 --- a/monitor/monitor.c +++ b/monitor/monitor.c @@ -367,14 +367,33 @@ monitor_qapi_event_queue_no_reenter(QAPIEvent event, = QDict *qdict) { MonitorQAPIEventConf *evconf; MonitorQAPIEventState *evstate; + bool throttled; =20 assert(event < QAPI_EVENT__MAX); evconf =3D &monitor_qapi_event_conf[event]; trace_monitor_protocol_event_queue(event, qdict, evconf->rate); + throttled =3D evconf->rate; + + /* + * Rate limit BLOCK_IO_ERROR only for action !=3D "stop". + * + * If the VM is stopped after an I/O error, this is important informat= ion + * for the management tool to keep track of the state of QEMU and we c= an't + * merge any events. At the same time, stopping the VM means that the = guest + * can't send additional requests and the number of events is already + * limited, so we can do without rate limiting. + */ + if (event =3D=3D QAPI_EVENT_BLOCK_IO_ERROR) { + QDict *data =3D qobject_to(QDict, qdict_get(qdict, "data")); + const char *action =3D qdict_get_str(data, "action"); + if (!strcmp(action, "stop")) { + throttled =3D false; + } + } =20 QEMU_LOCK_GUARD(&monitor_lock); =20 - if (!evconf->rate) { + if (!throttled) { /* Unthrottled event */ monitor_qapi_event_emit(event, qdict); } else { --=20 2.53.0