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block: make BDRV_POLL_WHILE() re-entrancy safe

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Nested BDRV_POLL_WHILE() calls can occur.  Currently
assert(!wait_->wakeup) fails in AIO_WAIT_WHILE() when this happens.

This patch converts the bool wait_->need_kick flag to an unsigned
wait_->num_waiters counter.

Nesting works correctly because outer AIO_WAIT_WHILE() callers evaluate
the condition again after the inner caller completes (invoking the inner
caller counts as aio_poll() progress).

Reported-by: "fuweiwei (C)" <fuweiwei2@huawei.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20180307124619.6218-1-stefanha@redhat.com
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2018-03-07 12:46:19 +00:00
parent e4ae62b802
commit 7376eda7c2
2 changed files with 31 additions and 32 deletions
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2
util/aio-wait.c
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@ -34,7 +34,7 @@ static void dummy_bh_cb(void *opaque)
void aio_wait_kick(AioWait *wait)
{
/* The barrier (or an atomic op) is in the caller. */
if (atomic_read(&wait->need_kick)) {
if (atomic_read(&wait->num_waiters)) {
aio_bh_schedule_oneshot(qemu_get_aio_context(), dummy_bh_cb, NULL);
}
}