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69de48445a
tests/test-bdrv-drain can hang in tests/iothread.c:iothread_run():
while (!atomic_read(&iothread->stopping)) {
aio_poll(iothread->ctx, true);
}
The iothread_join() function works as follows:
void iothread_join(IOThread *iothread)
{
iothread->stopping = true;
aio_notify(iothread->ctx);
qemu_thread_join(&iothread->thread);
If iothread_run() checks iothread->stopping before the iothread_join()
thread sets stopping to true, then aio_notify() may be optimized away
and iothread_run() hangs forever in aio_poll().
The correct way to change iothread->stopping is from a BH that executes
within iothread_run(). This ensures that iothread->stopping is checked
after we set it to true.
This was already fixed for ./iothread.c (note this is a different source
file!) by commit 2362a28ea1 ("iothread:
fix iothread_stop() race condition"), but not for tests/iothread.c.
Fixes: 0c330a734b
("aio: introduce aio_co_schedule and aio_co_wake")
Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20191003100103.331-1-stefanha@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
98 lines
2.4 KiB
C
98 lines
2.4 KiB
C
/*
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* Event loop thread implementation for unit tests
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*
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* Copyright Red Hat Inc., 2013, 2016
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*
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* Authors:
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* Stefan Hajnoczi <stefanha@redhat.com>
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* Paolo Bonzini <pbonzini@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*
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*/
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#include "qemu/osdep.h"
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#include "qapi/error.h"
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#include "block/aio.h"
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#include "qemu/main-loop.h"
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#include "qemu/rcu.h"
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#include "iothread.h"
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struct IOThread {
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AioContext *ctx;
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QemuThread thread;
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QemuMutex init_done_lock;
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QemuCond init_done_cond; /* is thread initialization done? */
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bool stopping;
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};
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static __thread IOThread *my_iothread;
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AioContext *qemu_get_current_aio_context(void)
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{
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return my_iothread ? my_iothread->ctx : qemu_get_aio_context();
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}
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static void *iothread_run(void *opaque)
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{
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IOThread *iothread = opaque;
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rcu_register_thread();
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my_iothread = iothread;
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qemu_mutex_lock(&iothread->init_done_lock);
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iothread->ctx = aio_context_new(&error_abort);
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qemu_cond_signal(&iothread->init_done_cond);
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qemu_mutex_unlock(&iothread->init_done_lock);
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while (!atomic_read(&iothread->stopping)) {
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aio_poll(iothread->ctx, true);
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}
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rcu_unregister_thread();
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return NULL;
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}
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static void iothread_stop_bh(void *opaque)
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{
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IOThread *iothread = opaque;
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iothread->stopping = true;
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}
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void iothread_join(IOThread *iothread)
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{
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aio_bh_schedule_oneshot(iothread->ctx, iothread_stop_bh, iothread);
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qemu_thread_join(&iothread->thread);
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qemu_cond_destroy(&iothread->init_done_cond);
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qemu_mutex_destroy(&iothread->init_done_lock);
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aio_context_unref(iothread->ctx);
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g_free(iothread);
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}
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IOThread *iothread_new(void)
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{
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IOThread *iothread = g_new0(IOThread, 1);
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qemu_mutex_init(&iothread->init_done_lock);
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qemu_cond_init(&iothread->init_done_cond);
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qemu_thread_create(&iothread->thread, NULL, iothread_run,
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iothread, QEMU_THREAD_JOINABLE);
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/* Wait for initialization to complete */
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qemu_mutex_lock(&iothread->init_done_lock);
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while (iothread->ctx == NULL) {
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qemu_cond_wait(&iothread->init_done_cond,
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&iothread->init_done_lock);
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}
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qemu_mutex_unlock(&iothread->init_done_lock);
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return iothread;
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}
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AioContext *iothread_get_aio_context(IOThread *iothread)
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{
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return iothread->ctx;
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}
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