From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51600) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1avtZZ-0002i8-LI for qemu-devel@nongnu.org; Thu, 28 Apr 2016 17:34:10 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1avtZY-0005RT-JR for qemu-devel@nongnu.org; Thu, 28 Apr 2016 17:34:09 -0400 Received: from mail-lf0-x22c.google.com ([2a00:1450:4010:c07::22c]:35125) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1avtZY-0005RI-CM for qemu-devel@nongnu.org; Thu, 28 Apr 2016 17:34:08 -0400 Received: by mail-lf0-x22c.google.com with SMTP id c126so111928968lfb.2 for ; Thu, 28 Apr 2016 14:34:08 -0700 (PDT) From: Sergey Fedorov Date: Fri, 29 Apr 2016 00:33:50 +0300 Message-Id: <1461879235-7694-6-git-send-email-sergey.fedorov@linaro.org> In-Reply-To: <1461879235-7694-1-git-send-email-sergey.fedorov@linaro.org> References: <1461879235-7694-1-git-send-email-sergey.fedorov@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: [Qemu-devel] [PATCH v5 05/10] 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: =?UTF-8?q?Alex=20Benn=C3=A9e?= , Sergey Fedorov , Paolo Bonzini , Peter Crosthwaite , Richard Henderson , Sergey Fedorov 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 Reviewed-by: Alex Bennée --- 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 | 29 ++++++++++++++++------------- 1 file changed, 16 insertions(+), 13 deletions(-) diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h index 64c2a660bcb2..06da1bcc45bf 100644 --- a/include/exec/exec-all.h +++ b/include/exec/exec-all.h @@ -372,20 +372,23 @@ 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]) { - qemu_log_mask_and_addr(CPU_LOG_EXEC, tb->pc, - "Linking TBs %p [" TARGET_FMT_lx - "] index %d -> %p [" TARGET_FMT_lx "]\n", - tb->tc_ptr, tb->pc, n, - tb_next->tc_ptr, tb_next->pc); - /* 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; - 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; } + qemu_log_mask_and_addr(CPU_LOG_EXEC, tb->pc, + "Linking TBs %p [" TARGET_FMT_lx + "] index %d -> %p [" TARGET_FMT_lx "]\n", + tb->tc_ptr, tb->pc, n, + tb_next->tc_ptr, tb_next->pc); + + /* 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; + tb_next->jmp_list_first = (uintptr_t)tb | n; } /* GETRA is the true target of the return instruction that we'll execute, -- 2.8.1