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authorMarkus Armbruster <armbru@redhat.com>2009-07-28 14:33:41 -0400
committerAnthony Liguori <aliguori@us.ibm.com>2009-07-30 09:50:37 -0500
commit213189ab65d83ecd9072f27c80a15dcb91b6bdbf (patch)
tree13a4609577ddab8d5a9aa7cae41172a77a3fae4d /qemu.sasl
parent3e28c9adf4bfe2f4792557ee45684181bd6e6d1c (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>
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