From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58035) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cUd3w-0002i1-0a for qemu-devel@nongnu.org; Fri, 20 Jan 2017 12:33:21 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cUd3s-0004s1-2T for qemu-devel@nongnu.org; Fri, 20 Jan 2017 12:33:20 -0500 Received: from mail-wm0-x231.google.com ([2a00:1450:400c:c09::231]:38721) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1cUd3r-0004qb-Rn for qemu-devel@nongnu.org; Fri, 20 Jan 2017 12:33:16 -0500 Received: by mail-wm0-x231.google.com with SMTP id r144so54795824wme.1 for ; Fri, 20 Jan 2017 09:33:14 -0800 (PST) References: <000301d259dc$f9d097c0$ed71c740$@ru> <000601d25a95$12b1b9f0$38152dd0$@ru> <20161220102126.GE5602@stefanha-x1.localdomain> <002501d25ab1$af024b00$0d06e100$@ru> <000301d25b4f$20018440$60048cc0$@ru> <000801d26bd9$dca56db0$95f04910$@ru> <87o9zd3jta.fsf@linaro.org> <000e01d26caa$dfdb3150$9f9193f0$@ru> From: Alex =?utf-8?Q?Benn=C3=A9e?= In-reply-to: <000e01d26caa$dfdb3150$9f9193f0$@ru> Date: Fri, 20 Jan 2017 17:33:11 +0000 Message-ID: <87mveleiw8.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] qemu-2.8-rc4 is broken List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Pavel Dovgalyuk Cc: 'Stefan Hajnoczi' , 'qemu-devel' , 'Paolo Bonzini' , 'Pavel Dovgalyuk' , 'Peter Maydell' Pavel Dovgalyuk writes: >> From: Alex Bennée [mailto:alex.bennee@linaro.org] >> >> From: Stefan Hajnoczi [mailto:stefanha@gmail.com] >> >> > >> >> > Yes, this option helps. >> >> > Thank you. >> >> >> >> Good news. This can be fixed in 2.8.1 once someone finds a solution. >> > >> > It seems that something still goes wrong. >> > I'm using this workaround, but there is a kind of deadlock in translation. >> > call_rcu_thread hangs at some moment in qemu_event_wait. >> > >> > As far as I understand, it is used by QHT in translate-all.c. >> > I can't get more information yet, because logging makes everything too slow. >> >> There are a number of users of RCU bit for QHT I think it only gets >> activated when it needs to re-size its hash table on insertion of new >> TranslationBlocks. >> >> Can you get a backtrace of all threads when it deadlocks? > > Sorry, this is another problem which occurs only in icount replay mode: > 1. cpu_handle_exception tries to force exception when is cannot occur due to > running out all the planned instructions: > } else if (replay_has_exception() > && cpu->icount_decr.u16.low + cpu->icount_extra == 0) { > /* try to cause an exception pending in the log */ > cpu_exec_nocache(cpu, 1, tb_find(cpu, NULL, 0), true); > *ret = -1; > return true; > > 2. tb_find calls tb_gen_code, which cannot allocate new translation block > and calls tb_flush (which only queues the flushing) and cpu_loop_exit > 3. cpu_loop_exit returns to infinite loop of cpu_exec and the condition > if (cpu_handle_exception(cpu, &ret)) { > break; > } > is checked again causing an infinite loop. > > TB cache is not flushed because we never execute that break and real work of tb_flush > is made outside this loop. I think what we need is a: if (cpu->exit_request) break; before the cpu_handle_exception() call to ensure any queued work gets processed first. Can you give me you current command line so I can reproduce this and check the fix works? -- Alex Bennée