Re: [Qemu-devel] [RFC v2 04/11] tcg: comment on which functions have to be called with tb_lock held

[Sergey Fedorov <serge.fdrv@gmail.com>]

On 05/05/16 18:03, Alex Bennée wrote:
> Sergey Fedorov <serge.fdrv@gmail.com> writes:
>
>> On 05/04/16 18:32, Alex Bennée wrote:
>>> diff --git a/exec.c b/exec.c
>>> index f46e596..17f390e 100644
>>> --- a/exec.c
>>> +++ b/exec.c
>>> @@ -826,6 +826,7 @@ int cpu_breakpoint_insert(CPUState *cpu, vaddr pc, int flags,
>>>  {
>>>      CPUBreakpoint *bp;
>>>
>>> +    /* TODO: locking (RCU?) */
>>>      bp = g_malloc(sizeof(*bp));
>>>
>>>      bp->pc = pc;
>> This comment is a little inconsistent. We should make access to
>> breakpoint and watchpoint lists to be thread-safe in all the functions
>> using them. So if we note this, it should be noted in all such places.
>> Also, it's probably not a good idea to put such comment just above
>> g_malloc() invocation, it could be a bit confusing. A bit more details
>> would also be nice.
> Good point.
>
> I could really do with some tests to exercise the debugging interface. I
> did some when I wrote the arm kvm GDB stuff (see
> 261f4d6d3e5445f887e070f047968e756c30cf06) but it is a) not plumbed in
> and b) not really a stress test which is what you want to be sure your
> handling is thread safe.

It seems we can only have a race between TCG helper inserting/removing
break-/watchpoint and gdbstub. So maybe we could just use separate lists
for CPU and GDB breakpoints?

Kind regards,
Sergey