[Qemu-devel] Re: Strange virtio regression on mainline and stable-0.10

[Avi Kivity <avi@redhat.com>]

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(re-added qemu-devel)

Kevin Wolf wrote:
> Avi Kivity schrieb:
>   
>> Running the Fedora 10 installer on a virtio disk on current master and 
>> on v0.10.3 will cause the installer to complain when mounting the 
>> freshly formatted filesystems. 
>>     
>
> Could be related to https://bugzilla.redhat.com/show_bug.cgi?id=498405
>
>   

It appears to be the same.

> I encountered IO errors with qcow2 and virtio this morning, so I already
> wanted to start debugging it. Unfortunately, with current master extboot
> seems to be broken for me and so I can't even boot with virtio. Have not
> figured out yet what's going wrong here.
>   

I'm using the installer so I don't depend on extboot.  Of course the 
extboot issue needs to be fixed as well.

>> I don't understand it, as free_any_clusters() shouldn't be called while 
>> formatting.  Any ideas?
>>     
>
> free_any_clusters shouldn't be called at all without snapshots or
> backing files.
>
> qemu-img check notices refcount errors on my broken image though, so
> this could still be the same.

data point: if I force writes to be serialized in block-qcow2.c, then 
everything works, and there are no calls to free_any_clusters().  It's 
likely that there is some lack of serialization in the allocation code, 
some write that is in flight does not update the global state, only 
acb-local state.

-- 
error compiling committee.c: too many arguments to function


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diff --git a/block-qcow2.c b/block-qcow2.c
index c4cd38d..151e688 100644
--- a/block-qcow2.c
+++ b/block-qcow2.c
@@ -1443,6 +1443,9 @@ static BlockDriverAIOCB *qcow_aio_readv(BlockDriverState *bs,
     return &acb->common;
 }
 
+static int nb_writes;
+static BlockDriverAIOCB *pending_writes[300];
+
 static void qcow_aio_write_cb(void *opaque, int ret)
 {
     QCowAIOCB *acb = opaque;
@@ -1518,6 +1521,18 @@ done:
         qemu_vfree(acb->orig_buf);
     acb->common.cb(acb->common.opaque, ret);
     qemu_aio_release(acb);
+
+    {
+        int i;
+
+        for (i = 1; i < nb_writes; ++i) {
+            pending_writes[i - 1] = pending_writes[i];
+        }
+        --nb_writes;
+        if (nb_writes) {
+            qcow_aio_write_cb(pending_writes[0], 0);
+        }
+    }
 }
 
 static BlockDriverAIOCB *qcow_aio_writev(BlockDriverState *bs,
@@ -1535,7 +1550,12 @@ static BlockDriverAIOCB *qcow_aio_writev(BlockDriverState *bs,
     if (!acb)
         return NULL;
 
-    qcow_aio_write_cb(acb, 0);
+    pending_writes[nb_writes++] = acb;
+
+    if (nb_writes == 1) {
+        qcow_aio_write_cb(acb, 0);
+    }
+
     return &acb->common;
 }