Re: [PATCH] Fix QEMU vcpu thread race with apic_reset

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

* Ryan Harper <ryanh@us.ibm.com> [2008-04-26 00:27]:
> There is a race between when the vcpu thread issues a create ioctl and when
> apic_reset() gets called resulting in getting a badfd error.
> 
> main thread                vcpu thread

guilt refresh clipped my text short.


main thread                vcpu thread
-----------                -----------
qemu/hw/pc.c:pc_new_cpu()
cpu_init()
cpu_x86_init()
kvm_init_new_ap()          ap_main_loop()
                              *blocks*
usleep()
apic_init()
kvm_set_lapic()
kvm_ioctl with unitilized context
badfd

To fix this, ensure we create the vcpu in the vcpu thread before returning from
kvm_init_new_ap.  Synchronize on a new mutux, vcpu_mutex, and wait for the
vcpuup condition before signaling to ensure the main thread is waiting before we
send the signal.

With this patch, I can launch 64 kvm guests, 1 second apart and not see any Bad
File descriptor errors.

Signed-off-by: Ryan Harper <ryanh@us.ibm.com>


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

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