diff options
| 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 | |
| parent | f6b06fcceef465de0cf2514c9f76fe0192896781 (diff) | |
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>
| -rw-r--r-- | block/throttle-groups.c | 9 | ||||
| -rw-r--r-- | include/block/throttle-groups.h | 5 |
2 files changed, 14 insertions, 0 deletions
diff --git a/block/throttle-groups.c b/block/throttle-groups.c index 5d8213a443..a5a2037924 100644 --- a/block/throttle-groups.c +++ b/block/throttle-groups.c @@ -415,6 +415,9 @@ static void coroutine_fn throttle_group_restart_queue_entry(void *opaque) } g_free(data); + + atomic_dec(&tgm->restart_pending); + aio_wait_kick(); } static void throttle_group_restart_queue(ThrottleGroupMember *tgm, bool is_write) @@ -430,6 +433,8 @@ static void throttle_group_restart_queue(ThrottleGroupMember *tgm, bool is_write * be no timer pending on this tgm at this point */ assert(!timer_pending(tgm->throttle_timers.timers[is_write])); + atomic_inc(&tgm->restart_pending); + co = qemu_coroutine_create(throttle_group_restart_queue_entry, rd); aio_co_enter(tgm->aio_context, co); } @@ -538,6 +543,7 @@ void throttle_group_register_tgm(ThrottleGroupMember *tgm, tgm->throttle_state = ts; tgm->aio_context = ctx; + atomic_set(&tgm->restart_pending, 0); qemu_mutex_lock(&tg->lock); /* If the ThrottleGroup is new set this ThrottleGroupMember as the token */ @@ -584,6 +590,9 @@ void throttle_group_unregister_tgm(ThrottleGroupMember *tgm) return; } + /* Wait for throttle_group_restart_queue_entry() coroutines to finish */ + AIO_WAIT_WHILE(tgm->aio_context, atomic_read(&tgm->restart_pending) > 0); + qemu_mutex_lock(&tg->lock); for (i = 0; i < 2; i++) { assert(tgm->pending_reqs[i] == 0); diff --git a/include/block/throttle-groups.h b/include/block/throttle-groups.h index e2fd0513c4..712a8e64b4 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. */ |