Re: [Qemu-devel] [PATCH 5/8] tcg: Clarify "thread safaty" check in tb_add_jump()

[Artyom Tarasenko]

s/safaty/safety/ ?

On Thu, Mar 24, 2016 at 11:39 AM,  <address@hidden> wrote:
> From: Sergey Fedorov <address@hidden>
>
> The check does not give an absolute guarantee of thread safety because
> there still may be a race condition between two threads which both have
> just read zero from jmp_list_next[n] and proceed with list modification.
> Clarify this in the comment to attract here some attention.
>
> Signed-off-by: Sergey Fedorov <address@hidden>
> Signed-off-by: Sergey Fedorov <address@hidden>
> ---
>  include/exec/exec-all.h | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
> index cd96219a89e7..4f36d109ac7f 100644
> --- a/include/exec/exec-all.h
> +++ b/include/exec/exec-all.h
> @@ -390,7 +390,10 @@ static inline void tb_set_jmp_target(TranslationBlock 
> *tb,
>  static inline void tb_add_jump(TranslationBlock *tb, int n,
>                                 TranslationBlock *tb_next)
>  {
> -    /* NOTE: this test is only needed for thread safety */
> +    /* FIXME: This test provides only some probablistic "thread safety" for
> +     * user-mode emulation; appropriate synchronization/locking scheme should
> +     * be implemented.
> +     */
>      if (!tb->jmp_list_next[n]) {
>          /* patch the native jump address */
>          tb_set_jmp_target(tb, n, (uintptr_t)tb_next->tc_ptr);
> --
> 2.7.3
>
>



-- 
Regards,
Artyom Tarasenko

SPARC and PPC PReP under qemu blog: http://tyom.blogspot.com/search/label/qemu