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Fix VM state change handlers running out of order

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When a VM state change handler changes VM state, other VM state change
handlers can see the state transitions out of order.

bmdma_map(), scsi_disk_init() and virtio_blk_init() install VM state
change handlers to restart DMA.  These handlers can vm_stop() by
running into a write error on a drive with werror=stop.  This throws
the VM state change handler callback into disarray.  Here's an example
case I observed:

0. The virtual IDE drive goes south.  All future writes return errors.

1. Something encounters a write error, and duly stops the VM with
   vm_stop().

2. vm_stop() calls vm_state_notify(0).

3. vm_state_notify() runs the callbacks in list vm_change_state_head.
   It contains ide_dma_restart_cb() installed by bmdma_map().  It also
   contains audio_vm_change_state_handler() installed by audio_init().

4. audio_vm_change_state_handler() stops audio stuff.

5. User continues VM with monitor command "c".  This runs vm_start().

6. vm_start() calls vm_state_notify(1).

7. vm_state_notify() runs the callbacks in vm_change_state_head.

8. ide_dma_restart_cb() happens to come first.  It does its work, runs
   into a write error, and duly stops the VM with vm_stop().

9. vm_stop() runs vm_state_notify(0).

10. vm_state_notify() runs the callbacks in vm_change_state_head.

11. audio_vm_change_state_handler() stops audio stuff.  Which isn't
   running.

12. vm_stop() finishes, ide_dma_restart_cb() finishes, step 7's
   vm_state_notify() resumes running handlers.

13. audio_vm_change_state_handler() starts audio stuff.  Oopsie.

Fix this by moving the actual write from each VM state change handler
into a new bottom half (suggested by Gleb Natapov).

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Markus Armbruster 2009-07-28 14:33:41 -04:00 • committed by Anthony Liguori
parent 3e28c9adf4
commit 213189ab65
3 changed files with 54 additions and 9 deletions
Download patch file Download diff file Expand all files Collapse all files

20
hw/virtio-blk.c
View file

@ -26,6 +26,7 @@ typedef struct VirtIOBlock
VirtQueue *vq;
void *rq;
char serial_str[BLOCK_SERIAL_STRLEN + 1];
QEMUBH *bh;
} VirtIOBlock;
static VirtIOBlock *to_virtio_blk(VirtIODevice *vdev)
@ -302,13 +303,13 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
*/
}
static void virtio_blk_dma_restart_cb(void *opaque, int running, int reason)
static void virtio_blk_dma_restart_bh(void *opaque)
{
VirtIOBlock *s = opaque;
VirtIOBlockReq *req = s->rq;
if (!running)
return;
qemu_bh_delete(s->bh);
s->bh = NULL;
s->rq = NULL;
@ -318,6 +319,19 @@ static void virtio_blk_dma_restart_cb(void *opaque, int running, int reason)
}
}
static void virtio_blk_dma_restart_cb(void *opaque, int running, int reason)
{
VirtIOBlock *s = opaque;
if (!running)
return;
if (!s->bh) {
s->bh = qemu_bh_new(virtio_blk_dma_restart_bh, s);
qemu_bh_schedule(s->bh);
}
}
static void virtio_blk_reset(VirtIODevice *vdev)
{
/*