path: root/iothread.c
diff options
authorPaolo Bonzini <pbonzini@redhat.com>2014-07-09 10:49:46 +0200
committerKevin Wolf <kwolf@redhat.com>2014-07-14 12:03:20 +0200
commitacfb23ad3dd8d0ab385a10e483776ba7dcf927ad (patch)
treed39d938ac8c90dafac2aaee9418cd557d15caef7 /iothread.c
parentf897bf751fbd95e4015b95d202c706548586813a (diff)
AioContext: do not rely on aio_poll(ctx, true) result to end a loop
Currently, whenever aio_poll(ctx, true) has completed all pending work it returns true *and* the next call to aio_poll(ctx, true) will not block. This invariant has its roots in qemu_aio_flush()'s implementation as "while (qemu_aio_wait()) {}". However, qemu_aio_flush() does not exist anymore and bdrv_drain_all() is implemented differently; and this invariant is complicated to maintain and subtly different from the return value of GMainLoop's g_main_context_iteration. All calls to aio_poll(ctx, true) except one are guarded by a while() loop checking for a request to be incomplete, or a BlockDriverState to be idle. The one remaining call (in iothread.c) uses this to delay the aio_context_release/acquire pair until the AioContext is quiescent, however: - we can do the same just by using non-blocking aio_poll, similar to how vl.c invokes main_loop_wait - it is buggy, because it does not ensure that the AioContext is released between an aio_notify and the next time the iothread goes to sleep. This leads to hangs when stopping the dataplane thread. In the end, these semantics are a bad match for the current users of AioContext. So modify that one exception in iothread.c, which also fixes the hangs, as well as the testcase so that it use the same idiom as the actual QEMU code. Reported-by: Christian Borntraeger <borntraeger@de.ibm.com> Tested-by: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'iothread.c')
1 files changed, 4 insertions, 1 deletions
diff --git a/iothread.c b/iothread.c
index 1fbf9f1c49..d9403cf69e 100644
--- a/iothread.c
+++ b/iothread.c
@@ -30,6 +30,7 @@ typedef ObjectClass IOThreadClass;
static void *iothread_run(void *opaque)
IOThread *iothread = opaque;
+ bool blocking;
iothread->thread_id = qemu_get_thread_id();
@@ -38,8 +39,10 @@ static void *iothread_run(void *opaque)
while (!iothread->stopping) {
- while (!iothread->stopping && aio_poll(iothread->ctx, true)) {
+ blocking = true;
+ while (!iothread->stopping && aio_poll(iothread->ctx, blocking)) {
/* Progress was made, keep going */
+ blocking = false;