diff options
author | Markus Armbruster <armbru@redhat.com> | 2009-07-28 14:33:41 -0400 |
---|---|---|
committer | Anthony Liguori <aliguori@us.ibm.com> | 2009-07-30 09:50:37 -0500 |
commit | 213189ab65d83ecd9072f27c80a15dcb91b6bdbf (patch) | |
tree | 13a4609577ddab8d5a9aa7cae41172a77a3fae4d /hw/qdev.c | |
parent | 3e28c9adf4bfe2f4792557ee45684181bd6e6d1c (diff) |
Fix VM state change handlers running out of order
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>
Diffstat (limited to 'hw/qdev.c')
0 files changed, 0 insertions, 0 deletions