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Re: [PATCH 3/3] migration/postcopy: handle POSTCOPY_INCOMING_RUNNING cor
From: |
Wei Yang |
Subject: |
Re: [PATCH 3/3] migration/postcopy: handle POSTCOPY_INCOMING_RUNNING corner case properly |
Date: |
Wed, 9 Oct 2019 13:07:56 +0800 |
User-agent: |
Mutt/1.9.4 (2018-02-28) |
On Wed, Oct 09, 2019 at 12:12:25PM +0800, Peter Xu wrote:
>On Wed, Oct 09, 2019 at 09:02:04AM +0800, Wei Yang wrote:
>> On Tue, Oct 08, 2019 at 05:40:46PM +0100, Dr. David Alan Gilbert wrote:
>> >* Wei Yang (address@hidden) wrote:
>> >> Currently, we set PostcopyState blindly to RUNNING, even we found the
>> >> previous state is not LISTENING. This will lead to a corner case.
>> >>
>> >> First let's look at the code flow:
>> >>
>> >> qemu_loadvm_state_main()
>> >> ret = loadvm_process_command()
>> >> loadvm_postcopy_handle_run()
>> >> return -1;
>> >> if (ret < 0) {
>> >> if (postcopy_state_get() == POSTCOPY_INCOMING_RUNNING)
>> >> ...
>> >> }
>> >>
>> >> From above snippet, the corner case is loadvm_postcopy_handle_run()
>> >> always sets state to RUNNING. And then it checks the previous state. If
>> >> the previous state is not LISTENING, it will return -1. But at this
>> >> moment, PostcopyState is already been set to RUNNING.
>> >>
>> >> Then ret is checked in qemu_loadvm_state_main(), when it is -1
>> >> PostcopyState is checked. Current logic would pause postcopy and retry
>> >> if PostcopyState is RUNNING. This is not what we expect, because
>> >> postcopy is not active yet.
>> >>
>> >> This patch makes sure state is set to RUNNING only previous state is
>> >> LISTENING by introducing an old_state parameter in postcopy_state_set().
>> >> New state only would be set when current state equals to old_state.
>> >>
>> >> Signed-off-by: Wei Yang <address@hidden>
>> >
>> >OK, it's a shame to use a pointer there, but it works.
>>
>> You mean second parameter of postcopy_state_set()?
>>
>> I don't have a better idea. Or we introduce a new state
>> POSTCOPY_INCOMING_NOCHECK. Do you feel better with this?
>
>Maybe simply fix loadvm_postcopy_handle_run() to set the state after
>the POSTCOPY_INCOMING_LISTENING check?
>
Set state back to ps if ps is not POSTCOPY_INCOMING_LISTENING?
Sounds like another option.
--
Wei Yang
Help you, Help me
- [PATCH 2/3] migration/postcopy: not necessary to do postcopy_ram_incoming_cleanup when state is ADVISE, (continued)
- [PATCH 1/3] migration/postcopy: rename postcopy_ram_enable_notify to postcopy_ram_incoming_setup, Wei Yang, 2019/10/01
- [PATCH 3/3] migration/postcopy: handle POSTCOPY_INCOMING_RUNNING corner case properly, Wei Yang, 2019/10/01
- Re: [PATCH 3/3] migration/postcopy: handle POSTCOPY_INCOMING_RUNNING corner case properly, Dr. David Alan Gilbert, 2019/10/08
- Re: [PATCH 3/3] migration/postcopy: handle POSTCOPY_INCOMING_RUNNING corner case properly, Wei Yang, 2019/10/08
- Re: [PATCH 3/3] migration/postcopy: handle POSTCOPY_INCOMING_RUNNING corner case properly, Peter Xu, 2019/10/09
- Re: [PATCH 3/3] migration/postcopy: handle POSTCOPY_INCOMING_RUNNING corner case properly,
Wei Yang <=
- Re: [PATCH 3/3] migration/postcopy: handle POSTCOPY_INCOMING_RUNNING corner case properly, Peter Xu, 2019/10/09
- Re: [PATCH 3/3] migration/postcopy: handle POSTCOPY_INCOMING_RUNNING corner case properly, Wei Yang, 2019/10/09
- Re: [PATCH 3/3] migration/postcopy: handle POSTCOPY_INCOMING_RUNNING corner case properly, Dr. David Alan Gilbert, 2019/10/09
- Re: [PATCH 3/3] migration/postcopy: handle POSTCOPY_INCOMING_RUNNING corner case properly, Wei Yang, 2019/10/09