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dma-helpers: ensure AIO callback is invoked after cancellation 

dma_aio_cancel unschedules the BH if there is one, which corresponds
to the reschedule_dma case of dma_blk_cb.  This can stall the DMA
permanently, because dma_complete will never get invoked and therefore
nobody will ever invoke the original AIO callback in dbs->common.cb.

Fix this by invoking the callback (which is ensured to happen after
a bdrv_aio_cancel_async, or done manually in the dbs->bh case), and
add assertions to check that the DMA state machine is indeed waiting
for dma_complete or reschedule_dma, but never both.

Reported-by: John Snow <jsnow@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20190729213416.1972-1-pbonzini@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>
This commit is contained in:
Paolo Bonzini 2019-07-29 23:34:16 +02:00 committed by John Snow
parent afd7605393
commit 539343c0a4
1 changed files with 9 additions and 4 deletions
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13
dma-helpers.c
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@ -90,6 +90,7 @@ static void reschedule_dma(void *opaque)
{
DMAAIOCB *dbs = (DMAAIOCB *)opaque;
assert(!dbs->acb && dbs->bh);
qemu_bh_delete(dbs->bh);
dbs->bh = NULL;
dma_blk_cb(dbs, 0);
@ -111,15 +112,12 @@ static void dma_complete(DMAAIOCB *dbs, int ret)
{
trace_dma_complete(dbs, ret, dbs->common.cb);
assert(!dbs->acb && !dbs->bh);
dma_blk_unmap(dbs);
if (dbs->common.cb) {
dbs->common.cb(dbs->common.opaque, ret);
}
qemu_iovec_destroy(&dbs->iov);
if (dbs->bh) {
qemu_bh_delete(dbs->bh);
dbs->bh = NULL;
}
qemu_aio_unref(dbs);
}
@ -179,14 +177,21 @@ static void dma_aio_cancel(BlockAIOCB *acb)
trace_dma_aio_cancel(dbs);
assert(!(dbs->acb && dbs->bh));
if (dbs->acb) {
/* This will invoke dma_blk_cb. */
blk_aio_cancel_async(dbs->acb);
return;
}
if (dbs->bh) {
cpu_unregister_map_client(dbs->bh);
qemu_bh_delete(dbs->bh);
dbs->bh = NULL;
}
if (dbs->common.cb) {
dbs->common.cb(dbs->common.opaque, -ECANCELED);
}
}
static AioContext *dma_get_aio_context(BlockAIOCB *acb)