From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45358) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ajDGD-0000AD-7j for qemu-devel@nongnu.org; Thu, 24 Mar 2016 17:57:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ajDGC-0008TP-Bk for qemu-devel@nongnu.org; Thu, 24 Mar 2016 17:57:45 -0400 Received: from mail-lb0-x22a.google.com ([2a00:1450:4010:c04::22a]:33790) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ajDGC-0008TJ-3w for qemu-devel@nongnu.org; Thu, 24 Mar 2016 17:57:44 -0400 Received: by mail-lb0-x22a.google.com with SMTP id oe12so39409149lbc.0 for ; Thu, 24 Mar 2016 14:57:43 -0700 (PDT) From: sergey.fedorov@linaro.org Date: Fri, 25 Mar 2016 00:56:44 +0300 Message-Id: <1458856607-3275-6-git-send-email-sergey.fedorov@linaro.org> In-Reply-To: <1458856607-3275-1-git-send-email-sergey.fedorov@linaro.org> References: <1458856607-3275-1-git-send-email-sergey.fedorov@linaro.org> Subject: [Qemu-devel] [PATCH v2 5/8] tcg: Clarify thread safety 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 is to make sure that another thread hasn't already done the same while we were outside of tb_lock. Mention this in a comment. Signed-off-by: Sergey Fedorov Signed-off-by: Sergey Fedorov --- Notes: Changes in v2: * Typo fixed in the commit title * Complete rewrite of the commit body and the patch based on Paolo's comments include/exec/exec-all.h | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h index db5c658919ad..45142ebab9e2 100644 --- a/include/exec/exec-all.h +++ b/include/exec/exec-all.h @@ -391,16 +391,19 @@ 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 */ - if (!tb->jmp_list_next[n]) { - /* patch the native jump address */ - tb_set_jmp_target(tb, n, (uintptr_t)tb_next->tc_ptr); - - /* add in TB jmp circular list */ - tb->jmp_list_next[n] = tb_next->jmp_list_first; - assert(((uintptr_t)tb & 3) == 0); - tb_next->jmp_list_first = (uintptr_t)tb | n; + if (tb->jmp_list_next[n]) { + /* Another thread has already done this while we were + * outside of the lock; nothing to do in this case */ + return; } + + /* patch the native jump address */ + tb_set_jmp_target(tb, n, (uintptr_t)tb_next->tc_ptr); + + /* add in TB jmp circular list */ + tb->jmp_list_next[n] = tb_next->jmp_list_first; + assert(((uintptr_t)tb & 3) == 0); + tb_next->jmp_list_first = (uintptr_t)tb | n; } /* GETRA is the true target of the return instruction that we'll execute, -- 2.7.3