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| author | Stefan Hajnoczi <stefanha@redhat.com> | 2019-01-14 13:32:56 +0000 |
|---|---|---|
| committer | Stefan Hajnoczi <stefanha@redhat.com> | 2019-01-24 10:02:28 +0000 |
| commit | bc19a0a6e4505390f99d3c593ebaf11b7962cc59 (patch) | |
| tree | 623290bec16d32e274dd740c46695ab4d5d0b635 /include | |
| parent | f6b06fcceef465de0cf2514c9f76fe0192896781 (diff) | |
| download | qemu-bc19a0a6e4505390f99d3c593ebaf11b7962cc59.zip qemu-bc19a0a6e4505390f99d3c593ebaf11b7962cc59.tar.gz qemu-bc19a0a6e4505390f99d3c593ebaf11b7962cc59.tar.bz2 | |
throttle-groups: fix restart coroutine iothread race
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>
Diffstat (limited to 'include')
| -rw-r--r-- | include/block/throttle-groups.h | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/include/block/throttle-groups.h b/include/block/throttle-groups.h index e2fd051..712a8e6 100644 --- a/include/block/throttle-groups.h +++ b/include/block/throttle-groups.h @@ -43,6 +43,11 @@ typedef struct ThrottleGroupMember { */ unsigned int io_limits_disabled; + /* Number of pending throttle_group_restart_queue_entry() coroutines. + * Accessed with atomic operations. + */ + unsigned int restart_pending; + /* The following fields are protected by the ThrottleGroup lock. * See the ThrottleGroup documentation for details. * throttle_state tells us if I/O limits are configured. */ |