On Tue, Dec 05, 2023 at 11:09:59AM +0100, Michal Suchánek wrote:
> On Mon, Dec 04, 2023 at 03:02:45PM -0800, Richard Henderson wrote:
> > On 12/4/23 12:09, Michal Suchánek wrote:
> > > On Mon, Dec 04, 2023 at 02:50:17PM -0500, Stefan Hajnoczi wrote:
> > > > On Mon, 4 Dec 2023 at 14:40, Philippe Mathieu-Daudé <phi...@linaro.org>
> > > > wrote:
> > > > > +void tcg_unregister_thread(void)
> > > > > +{
> > > > > + unsigned int n;
> > > > > +
> > > > > + n = qatomic_fetch_dec(&tcg_cur_ctxs);
> > > > > + g_free(tcg_ctxs[n]);
> > > > > + qatomic_set(&tcg_ctxs[n], NULL);
> > > > > +}
> > > >
> > > > tcg_ctxs[n] may not be our context, so this looks like it could free
> > > > another thread's context and lead to undefined behavior.
> >
> > Correct.
> >
> > > There is cpu->thread_id so perhaps cpu->thread_ctx could be added as
> > > well. That would require a bitmap of used threads contexts rather than a
> > > counter, though.
> >
> > Or don't free the context at all, but re-use it when incrementing and
> > tcg_ctxs[n] != null (i.e. plugging in a repacement vcpu). After all, there
> > can only be tcg_max_ctxs contexts.
>
> But you would not know which contexts are in use and which aren't without
> tracking the association of contexts to CPUs.
>
> Unless there is a cpu array somewhere and you can use the same index for
> both to create the association.
I tried to use cpu_index for correlating the tcg_ctx with cpu. I added
some asserts that only null contexts are allocated and non-null contexts
released but qemu crashes somewhere in tcg sometime after the guest gets
to switch root.
Thanks
Michal
