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[46.188.121.115]) by smtp.gmail.com with ESMTPSA id ub6sm1409964lbb.17.2016.04.20.14.15.35 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 20 Apr 2016 14:15:35 -0700 (PDT) From: Sergey Fedorov To: qemu-devel@nongnu.org Date: Thu, 21 Apr 2016 00:15:16 +0300 Message-Id: <1461186921-14977-6-git-send-email-sergey.fedorov@linaro.org> X-Mailer: git-send-email 2.8.1 In-Reply-To: <1461186921-14977-1-git-send-email-sergey.fedorov@linaro.org> References: <1461186921-14977-1-git-send-email-sergey.fedorov@linaro.org> MIME-Version: 1.0 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 2a00:1450:4010:c04::232 Subject: [Qemu-devel] [PATCH v4 05/10] tcg: Clarify thread safety check in tb_add_jump() X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Sergey Fedorov , Peter Crosthwaite , Paolo Bonzini , Sergey Fedorov , =?UTF-8?q?Alex=20Benn=C3=A9e?= , Richard Henderson Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" 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 03b177b0cac5..0e9f630b5a43 100644 --- a/include/exec/exec-all.h +++ b/include/exec/exec-all.h @@ -391,20 +391,23 @@ 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,