From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42942) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1apNBP-0002cu-0X for qemu-devel@nongnu.org; Sun, 10 Apr 2016 17:46:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1apNBM-0002wL-5g for qemu-devel@nongnu.org; Sun, 10 Apr 2016 17:46:14 -0400 Received: from mail-lf0-x234.google.com ([2a00:1450:4010:c07::234]:33084) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1apNBL-0002wG-TQ for qemu-devel@nongnu.org; Sun, 10 Apr 2016 17:46:12 -0400 Received: by mail-lf0-x234.google.com with SMTP id e190so131900936lfe.0 for ; Sun, 10 Apr 2016 14:46:11 -0700 (PDT) From: Sergey Fedorov Date: Mon, 11 Apr 2016 00:45:27 +0300 Message-Id: <1460324732-30330-6-git-send-email-sergey.fedorov@linaro.org> In-Reply-To: <1460324732-30330-1-git-send-email-sergey.fedorov@linaro.org> References: <1460324732-30330-1-git-send-email-sergey.fedorov@linaro.org> Subject: [Qemu-devel] [PATCH v3 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 --- 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 | 31 +++++++++++++++++-------------- 1 file changed, 17 insertions(+), 14 deletions(-) diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h index b055716ed690..8e81ef5fb2c2 100644 --- a/include/exec/exec-all.h +++ b/include/exec/exec-all.h @@ -391,21 +391,24 @@ 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; - 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; } + 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; + 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, -- 2.8.1