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The following QMP command leads to a crash when iothreads are used:
{ 'execute': 'device_del', 'arguments': {'id': 'data'} }
The backtrace involves the queue restart coroutine where
tgm->throttle_state is a NULL pointer because
throttle_group_unregister_tgm() has already been called:
(gdb) bt full
#0 0x00005585a7a3b378 in qemu_mutex_lock_impl (mutex=0xffffffffffffffd0, file=0x5585a7bb3d54 "block/throttle-groups.c", line=412) at util/qemu-thread-posix.c:64
err = <optimized out>
__PRETTY_FUNCTION__ = "qemu_mutex_lock_impl"
__func__ = "qemu_mutex_lock_impl"
#1 0x00005585a79be074 in throttle_group_restart_queue_entry (opaque=0x5585a9de4eb0) at block/throttle-groups.c:412
_f = <optimized out>
data = 0x5585a9de4eb0
tgm = 0x5585a9079440
ts = 0x0
tg = 0xffffffffffffff98
is_write = false
empty_queue = 255
This coroutine should not execute in the iothread after the throttle
group member has been unregistered!
The root cause is that the device_del code path schedules the restart
coroutine in the iothread while holding the AioContext lock. Therefore
the iothread cannot execute the coroutine until after device_del
releases the lock - by this time it's too late.
This patch adds a reference count to ThrottleGroupMember so we can
synchronously wait for restart coroutines to complete. Once they are
done it is safe to unregister the ThrottleGroupMember.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 20190114133257.30299-2-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
91 lines
3.2 KiB
C
91 lines
3.2 KiB
C
/*
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* QEMU block throttling group infrastructure
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*
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* Copyright (C) Nodalink, EURL. 2014
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* Copyright (C) Igalia, S.L. 2015
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*
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* Authors:
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* Benoît Canet <benoit.canet@nodalink.com>
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* Alberto Garcia <berto@igalia.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 or
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* (at your option) version 3 of the License.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef THROTTLE_GROUPS_H
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#define THROTTLE_GROUPS_H
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#include "qemu/throttle.h"
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#include "block/block_int.h"
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/* The ThrottleGroupMember structure indicates membership in a ThrottleGroup
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* and holds related data.
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*/
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typedef struct ThrottleGroupMember {
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AioContext *aio_context;
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/* throttled_reqs_lock protects the CoQueues for throttled requests. */
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CoMutex throttled_reqs_lock;
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CoQueue throttled_reqs[2];
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/* Nonzero if the I/O limits are currently being ignored; generally
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* it is zero. Accessed with atomic operations.
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*/
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unsigned int io_limits_disabled;
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/* Number of pending throttle_group_restart_queue_entry() coroutines.
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* Accessed with atomic operations.
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*/
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unsigned int restart_pending;
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/* The following fields are protected by the ThrottleGroup lock.
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* See the ThrottleGroup documentation for details.
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* throttle_state tells us if I/O limits are configured. */
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ThrottleState *throttle_state;
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ThrottleTimers throttle_timers;
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unsigned pending_reqs[2];
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QLIST_ENTRY(ThrottleGroupMember) round_robin;
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} ThrottleGroupMember;
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#define TYPE_THROTTLE_GROUP "throttle-group"
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#define THROTTLE_GROUP(obj) OBJECT_CHECK(ThrottleGroup, (obj), TYPE_THROTTLE_GROUP)
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const char *throttle_group_get_name(ThrottleGroupMember *tgm);
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ThrottleState *throttle_group_incref(const char *name);
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void throttle_group_unref(ThrottleState *ts);
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void throttle_group_config(ThrottleGroupMember *tgm, ThrottleConfig *cfg);
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void throttle_group_get_config(ThrottleGroupMember *tgm, ThrottleConfig *cfg);
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void throttle_group_register_tgm(ThrottleGroupMember *tgm,
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const char *groupname,
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AioContext *ctx);
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void throttle_group_unregister_tgm(ThrottleGroupMember *tgm);
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void throttle_group_restart_tgm(ThrottleGroupMember *tgm);
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void coroutine_fn throttle_group_co_io_limits_intercept(ThrottleGroupMember *tgm,
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unsigned int bytes,
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bool is_write);
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void throttle_group_attach_aio_context(ThrottleGroupMember *tgm,
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AioContext *new_context);
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void throttle_group_detach_aio_context(ThrottleGroupMember *tgm);
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/*
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* throttle_group_exists() must be called under the global
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* mutex.
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*/
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bool throttle_group_exists(const char *name);
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#endif
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