Re: [PATCH] Don't race while creating a VCPU

[Ryan Harper <ryanh@us.ibm.com>]

* Anthony Liguori <aliguori@us.ibm.com> [2008-04-28 17:30]:
> We hold qemu_mutex while machine->init() executes, which issues a VCPU create.
> We need to make sure to not return from the VCPU creation until the VCPU
> file descriptor is valid to ensure that APIC creation succeeds.
> 
> However, we also need to make sure that the VCPU thread doesn't start running
> until the machine->init() is complete.  This is addressed today because the
> VCPU thread tries to grab the qemu_mutex before doing anything interesting.
> If we release qemu_mutex to wait for VCPU creation, then we open a window for
> a race to occur.
> 
> This patch introduces two wait conditions.  The first lets the VCPU create
> code that runs in the IO thread to wait for a VCPU to initialize.  The second
> condition lets the VCPU thread wait for the machine to fully initialize before
> running.
> 
> An added benefit of this patch is it makes the dependencies now explicit.
> 
> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

This patch passed the same tests I used on the other: 64 1VCPU guest
launch, 1 second apart, and a 16-way SMP guest boot.

-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253
ryanh@us.ibm.com

-------------------------------------------------------------------------
This SF.net email is sponsored by the 2008 JavaOne(SM) Conference 
Don't miss this year's exciting event. There's still time to save $100. 
Use priority code J8TL2D2. 
http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone