aboutsummaryrefslogtreecommitdiff
path: root/block
diff options
context:
space:
mode:
authorStefan Hajnoczi <stefanha@redhat.com>2019-01-14 13:32:56 +0000
committerStefan Hajnoczi <stefanha@redhat.com>2019-01-24 10:02:28 +0000
commitbc19a0a6e4505390f99d3c593ebaf11b7962cc59 (patch)
tree623290bec16d32e274dd740c46695ab4d5d0b635 /block
parentf6b06fcceef465de0cf2514c9f76fe0192896781 (diff)
downloadqemu-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 'block')
-rw-r--r--block/throttle-groups.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/block/throttle-groups.c b/block/throttle-groups.c
index 5d8213a..a5a2037 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);