Re: [Qemu-devel] tb lock in qemu cpu-exec.c

[Peter Maydell]

On 21 January 2012 19:39, Xin Tong <address@hidden> wrote:
> There is a TB lock in the cpu-exec.c. It is held before a vcpu is
> trying to find the next tb it is trying to execute. I am wondering
> what this lock is for. Currently, qemu is time multiplexing on a host
> cpu to emulate smp. No other vcpu can be running while the tb
> lookup/translation is performed.

The thing that needs to be locked is (a) cpu thread is in this
cpu-exec.c code doing a lookup for a TB (b) another thread (io
thread) or signal handler (linux-user case) calls cpu_exit(),
which manipulates the TB links.

Unfortunately the tb_lock doesn't actually achieve this purpose;
it is just broken and there are race conditions here.

-- PMM