From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50294) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aj2gD-0001AS-HB for qemu-devel@nongnu.org; Thu, 24 Mar 2016 06:39:54 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aj2gC-0007tP-FW for qemu-devel@nongnu.org; Thu, 24 Mar 2016 06:39:53 -0400 Received: from mail-lb0-x22b.google.com ([2a00:1450:4010:c04::22b]:33358) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aj2gC-0007t5-8O for qemu-devel@nongnu.org; Thu, 24 Mar 2016 06:39:52 -0400 Received: by mail-lb0-x22b.google.com with SMTP id oe12so27546277lbc.0 for ; Thu, 24 Mar 2016 03:39:52 -0700 (PDT) From: sergey.fedorov@linaro.org Date: Thu, 24 Mar 2016 13:39:18 +0300 Message-Id: <1458815961-31979-6-git-send-email-sergey.fedorov@linaro.org> In-Reply-To: <1458815961-31979-1-git-send-email-sergey.fedorov@linaro.org> References: <1458815961-31979-1-git-send-email-sergey.fedorov@linaro.org> Subject: [Qemu-devel] [PATCH 5/8] tcg: Clarify "thread safaty" check in tb_add_jump() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Sergey Fedorov , Peter Crosthwaite , Paolo Bonzini , Sergey Fedorov , =?UTF-8?q?Alex=20Benn=C3=A9e?= , Richard Henderson From: Sergey Fedorov 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 Signed-off-by: Sergey Fedorov --- 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