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[Qemu-devel] [PATCH v2 2/2] block: asynchronously stop the VM on I/O err
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH v2 2/2] block: asynchronously stop the VM on I/O errors |
Date: |
Thu, 5 Jun 2014 14:53:59 +0200 |
With virtio-blk dataplane, I/O errors might occur while QEMU is
not in the main I/O thread. However, it's invalid to call vm_stop
when we're neither in a VCPU thread nor in the main I/O thread,
even if we were to take the iothread mutex around it.
To avoid this problem, we can raise a request to the main I/O thread,
similar to what QEMU does when vm_stop is called from a CPU thread.
We know that bdrv_error_action is called from an AIO callback, and
the moment at which the callback will fire is not well-defined; it
depends on the moment at which the disk or OS finishes the operation,
which can happen at any time. Note that QEMU is certainly not in a CPU
thread and we do not need to call cpu_stop_current() like vm_stop() does.
However, we need to ensure that any action taken by management will
result in correct detection of the error _and_ a running VM. In particular:
- the event must be raised after the iostatus has been set, so that
"info block" will return an iostatus that matches the event.
- the VM must be stopped after the iostatus has been set, so that
"info block" will return an iostatus that matches the runstate.
The ordering between the STOP and BLOCK_IO_ERROR events is preserved;
BLOCK_IO_ERROR is documented to come first.
This makes bdrv_error_action() thread safe (assuming QMP events are,
which is attacked by a separate series).
Signed-off-by: Paolo Bonzini <address@hidden>
---
block.c | 20 ++++++++++++++++++--
docs/qmp/qmp-events.txt | 2 +-
stubs/vm-stop.c | 7 ++++++-
3 files changed, 25 insertions(+), 4 deletions(-)
diff --git a/block.c b/block.c
index 17f763d..32082f6 100644
--- a/block.c
+++ b/block.c
@@ -3629,10 +3629,27 @@ void bdrv_error_action(BlockDriverState *bs,
BlockErrorAction action,
bool is_read, int error)
{
assert(error >= 0);
- bdrv_emit_qmp_error_event(bs, QEVENT_BLOCK_IO_ERROR, action, is_read);
+
if (action == BDRV_ACTION_STOP) {
- vm_stop(RUN_STATE_IO_ERROR);
+ /* First set the iostatus, so that "info block" returns an iostatus
+ * that matches the events raised so far (an additional error iostatus
+ * is fine, but not a lost one).
+ */
bdrv_iostatus_set_err(bs, error);
+
+ /* Then raise the request to stop the VM and the event.
+ * qemu_system_vmstop_request_prepare has two effects. First,
+ * it ensures that the STOP event always comes after the
+ * BLOCK_IO_ERROR event. Second, it ensures that even if management
+ * can observe the STOP event and do a "cont" before the STOP
+ * event is issued, the VM will not stop. In this case, vm_start()
+ * also ensures that the STOP/RESUME pair of events is emitted.
+ */
+ qemu_system_vmstop_request_prepare();
+ bdrv_emit_qmp_error_event(bs, QEVENT_BLOCK_IO_ERROR, action, is_read);
+ qemu_system_vmstop_request(RUN_STATE_IO_ERROR);
+ } else {
+ bdrv_emit_qmp_error_event(bs, QEVENT_BLOCK_IO_ERROR, action, is_read);
}
}
diff --git a/docs/qmp/qmp-events.txt b/docs/qmp/qmp-events.txt
index 145402e..849ec9d 100644
--- a/docs/qmp/qmp-events.txt
+++ b/docs/qmp/qmp-events.txt
@@ -52,7 +52,7 @@ Data:
- "action": action that has been taken, it's one of the following
(json-string):
"ignore": error has been ignored
"report": error has been reported to the device
- "stop": error caused VM to be stopped
+ "stop": the VM is going to stop because of the error
Example:
diff --git a/stubs/vm-stop.c b/stubs/vm-stop.c
index f82c897..69fd86b 100644
--- a/stubs/vm-stop.c
+++ b/stubs/vm-stop.c
@@ -1,7 +1,12 @@
#include "qemu-common.h"
#include "sysemu/sysemu.h"
-int vm_stop(RunState state)
+void qemu_system_vmstop_request_prepare(void)
+{
+ abort();
+}
+
+void qemu_system_vmstop_request(RunState state)
{
abort();
}
--
1.8.3.1