From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36858) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bIZKG-0005I0-8C for qemu-devel@nongnu.org; Thu, 30 Jun 2016 06:36:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bIZKC-0005SE-2D for qemu-devel@nongnu.org; Thu, 30 Jun 2016 06:36:03 -0400 Received: from mail-lf0-x243.google.com ([2a00:1450:4010:c07::243]:33228) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bIZKB-0005SA-MB for qemu-devel@nongnu.org; Thu, 30 Jun 2016 06:35:59 -0400 Received: by mail-lf0-x243.google.com with SMTP id l188so7962301lfe.0 for ; Thu, 30 Jun 2016 03:35:59 -0700 (PDT) References: <1466375313-7562-1-git-send-email-sergey.fedorov@linaro.org> <1466375313-7562-7-git-send-email-sergey.fedorov@linaro.org> <87lh1o0y1k.fsf@linaro.org> <5774E8C2.1050506@gmail.com> <87furvq85v.fsf@linaro.org> From: Sergey Fedorov Message-ID: <5774F60C.3010707@gmail.com> Date: Thu, 30 Jun 2016 13:35:56 +0300 MIME-Version: 1.0 In-Reply-To: <87furvq85v.fsf@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [RFC 6/8] linux-user: Support CPU work queue List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?UTF-8?Q?Alex_Benn=c3=a9e?= Cc: Sergey Fedorov , qemu-devel@nongnu.org, Riku Voipio , Peter Crosthwaite , patches@linaro.org, Paolo Bonzini , Richard Henderson On 30/06/16 13:32, Alex Bennée wrote: > Sergey Fedorov writes: > >> On 29/06/16 19:17, Alex Bennée wrote: >>> So I think there is a deadlock we can get with the async work: >>> >>> (gdb) thread apply all bt >>> >>> Thread 11 (Thread 0x7ffefeca7700 (LWP 2912)): >>> #0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185 >>> #1 0x00005555555cb777 in wait_cpu_work () at /home/alex/lsrc/qemu/qemu.git/linux-user/main.c:155 >>> #2 0x00005555555a0cee in wait_safe_cpu_work () at /home/alex/lsrc/qemu/qemu.git/cpu-exec-common.c:87 >>> #3 0x00005555555cb8fe in cpu_exec_end (cpu=0x555555bb67e0) at /home/alex/lsrc/qemu/qemu.git/linux-user/main.c:222 >>> #4 0x00005555555cc7a7 in cpu_loop (env=0x555555bbea58) at /home/alex/lsrc/qemu/qemu.git/linux-user/main.c:749 >>> #5 0x00005555555db0b2 in clone_func (arg=0x7fffffffc9c0) at /home/alex/lsrc/qemu/qemu.git/linux-user/syscall.c:5424 >>> #6 0x00007ffff6bed6fa in start_thread (arg=0x7ffefeca7700) at pthread_create.c:333 >>> #7 0x00007ffff6923b5d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109 >>> >>> >>> >>> Thread 3 (Thread 0x7ffff7f38700 (LWP 2904)): >>> #0 0x00005555555faf5d in safe_syscall_base () >>> #1 0x00005555555cfeaf in safe_futex (uaddr=0x7ffff528a0a4, op=128, val=1, timeout=0x0, uaddr2=0x0, val3=-162668384) >>> at /home/alex/lsrc/qemu/qemu.git/linux-user/syscall.c:706 >>> #2 0x00005555555dd7cc in do_futex (uaddr=4132298916, op=128, val=1, timeout=0, uaddr2=0, val3=-162668384) >>> at /home/alex/lsrc/qemu/qemu.git/linux-user/syscall.c:6246 >>> #3 0x00005555555e8cdb in do_syscall (cpu_env=0x555555a81118, num=240, arg1=-162668380, arg2=128, arg3=1, arg4=0, arg5=0, arg6=-162668384, >>> arg7=0, arg8=0) at /home/alex/lsrc/qemu/qemu.git/linux-user/syscall.c:10642 >>> #4 0x00005555555cd20e in cpu_loop (env=0x555555a81118) at /home/alex/lsrc/qemu/qemu.git/linux-user/main.c:883 >>> #5 0x00005555555db0b2 in clone_func (arg=0x7fffffffc9c0) at /home/alex/lsrc/qemu/qemu.git/linux-user/syscall.c:5424 >>> #6 0x00007ffff6bed6fa in start_thread (arg=0x7ffff7f38700) at pthread_create.c:333 >>> #7 0x00007ffff6923b5d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109 >>> >>> So everything is stalled awaiting this thread waking up and draining >>> its queue. So for linux-user I think we need some mechanism to kick >>> these syscalls which I assume means throwing a signal at it. >> Nice catch! How did you get it? > Running pigz (armhf, debian) to compress stuff. > >> We always go through cpu_exec_end() >> before serving a guest syscall and always go through cpu_exec_start() >> before entering the guest code execution loop. If we always schedule >> safe work on the current thread's queue then I think there's a way to >> make it safe and avoid kicking syscalls. > Not let the signals complete until safe work is done? I'm thinking of waiting for completion of safe works in cpu_exec_start() as well as in cpu_exec_end(). Regards, Sergey