[Xen-devel] Windows Bug Check 0x101 issue

[Kouya Shimura <kouya@xxxxxxxxxxxxxx>]

Hi,

Qemu-dm might be blocked with fsync system call over 3 seconds
when the dom0 is overloaded.

It causes SMP Windows 2008 crashes with Bug Check 0x101.
0x101 indicates that an expected clock interrupt on a secondary
processor, in a multi-processor system, was not received within
the allocated interval.

It can be easily reproduced with the following modification:

diff -r 76c9cf11ce23 tools/ioemu/block-raw.c
--- a/tools/ioemu/block-raw.c   Fri Mar 21 09:45:34 2008 +0000
+++ b/tools/ioemu/block-raw.c   Mon Mar 24 16:28:16 2008 +0900
@@ -603,6 +603,11 @@ static void raw_flush(BlockDriverState *
 static void raw_flush(BlockDriverState *bs)
 {
     BDRVRawState *s = bs->opaque;
+#if 1 /* reproduce Windows Bug Check 0x101 */
+    extern int send_vcpu;
+    if (send_vcpu != 0)
+       sleep(4);
+#endif
     fsync(s->fd);
 }
 
An attached patch fixes it. However I think the root cause is
that a timer event can't interrupt an i/o emulation.
How should we fix it?

Thanks,
Kouya

diff -r 76c9cf11ce23 tools/ioemu/block-raw.c
--- a/tools/ioemu/block-raw.c   Fri Mar 21 09:45:34 2008 +0000
+++ b/tools/ioemu/block-raw.c   Mon Mar 24 17:56:19 2008 +0900
@@ -496,6 +496,10 @@ static void raw_aio_cancel(BlockDriverAI
         pacb = &acb->next;
     }
 }
+
+static void aio_fsync_cb(void *opague, int ret)
+{
+}
 #endif
 
 static void raw_close(BlockDriverState *bs)
@@ -602,8 +606,20 @@ static int raw_create(const char *filena
 
 static void raw_flush(BlockDriverState *bs)
 {
+#ifdef NO_AIO
     BDRVRawState *s = bs->opaque;
     fsync(s->fd);
+#else
+    RawAIOCB *acb;
+
+    acb = raw_aio_setup(bs, 0, NULL, 0, aio_fsync_cb, NULL);
+    if (!acb)
+        return;
+    if (aio_fsync(O_SYNC, &acb->aiocb) < 0) {
+        qemu_aio_release(acb);
+        return;
+    }
+#endif
 }
 
 BlockDriver bdrv_raw = {

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