From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NmEBA-0001r1-KX for qemu-devel@nongnu.org; Mon, 01 Mar 2010 17:33:32 -0500 Received: from [199.232.76.173] (port=38331 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NmEB9-0001qh-Ff for qemu-devel@nongnu.org; Mon, 01 Mar 2010 17:33:31 -0500 Received: from Debian-exim by monty-python.gnu.org with spam-scanned (Exim 4.60) (envelope-from ) id 1NmEB8-0002sz-Ig for qemu-devel@nongnu.org; Mon, 01 Mar 2010 17:33:31 -0500 Received: from mail-fx0-f214.google.com ([209.85.220.214]:47100) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1NmEB8-0002sv-5o for qemu-devel@nongnu.org; Mon, 01 Mar 2010 17:33:30 -0500 Received: by fxm6 with SMTP id 6so3111557fxm.2 for ; Mon, 01 Mar 2010 14:33:29 -0800 (PST) Sender: Paolo Bonzini Message-ID: <4B8C40B3.6030008@redhat.com> Date: Mon, 01 Mar 2010 23:33:23 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <20100301213351.GN8952@hall.aurel32.net> In-Reply-To: <20100301213351.GN8952@hall.aurel32.net> Content-Type: multipart/mixed; boundary="------------070403060407070304010806" Subject: [Qemu-devel] Re: Regression: segfault on ARM host List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Aurelien Jarno Cc: qemu-devel This is a multi-part message in MIME format. --------------070403060407070304010806 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit On 03/01/2010 10:33 PM, Aurelien Jarno wrote: > While trying to implement setcond on TCG ARM, I have discovered it does > not work anymore. I have bisected this regression to: > > commit 6113d6d3169393c323ac4c82d756a850145a5e7a > Author: Paolo Bonzini > Date: Fri Jan 15 09:42:09 2010 +0100 > > change while to if > > The while loop will be executed exactly 0 or 1 times, depending on > env->exit_request. > > Signed-off-by: Paolo Bonzini > Signed-off-by: Anthony Liguori > > The assertion is actually triggered. When the next patch removing the > assertion is also applied it segfaults instead. Looks like a race. The only piece of logic that is changed by that commit is reverted in the attached patch, can you try it? If it passes, I can resubmit with S-o-b. If it doesn't pass, I wonder whether the while loop was there to trick the compiler into not optimizing something. Seems a bit too clever though. Paolo --------------070403060407070304010806 Content-Type: text/plain; name="qemu-race.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="qemu-race.patch" diff --git a/cpu-exec.c b/cpu-exec.c index 5d6dd51..61b1c59 100644 --- a/cpu-exec.c +++ b/cpu-exec.c @@ -602,9 +602,15 @@ int cpu_exec(CPUState *env1) /* cpu_interrupt might be called while translating the TB, but before it is linked into a potentially infinite loop and becomes env->current_tb. Avoid - starting execution if there is a pending interrupt. */ - if (!unlikely (env->exit_request)) { - env->current_tb = tb; + starting execution if there is a pending interrupt. + Doing it this way is necessary to avoid races with + cpu_unlink_tb (called by cpu_exit). */ + env->current_tb = tb; + if (unlikely (env->exit_request)) { + env->current_tb = NULL; + } + + if (likely (env->current_tb)) { tc_ptr = tb->tc_ptr; /* execute the generated code */ #if defined(__sparc__) && !defined(CONFIG_SOLARIS) --------------070403060407070304010806--