From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:38940) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SSD0b-0006R9-CB for qemu-devel@nongnu.org; Wed, 09 May 2012 15:57:14 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SSD0Z-0005mQ-Hc for qemu-devel@nongnu.org; Wed, 09 May 2012 15:57:12 -0400 Received: from david.siemens.de ([192.35.17.14]:32437) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SSD0Z-0005mF-3r for qemu-devel@nongnu.org; Wed, 09 May 2012 15:57:11 -0400 Message-ID: <4FAACC0F.9080702@siemens.com> Date: Wed, 09 May 2012 16:57:03 -0300 From: Jan Kiszka MIME-Version: 1.0 References: <4FAAC3A3.5040503@siemens.com> <4FAAC521.5000907@msgid.tls.msk.ru> <4FAAC6B2.7040009@siemens.com> <4FAACA0A.5040602@us.ibm.com> In-Reply-To: <4FAACA0A.5040602@us.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1.1] coroutine: Avoid ucontext usage on i386 Linux host List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: Kevin Wolf , Peter Maydell , Michael Tokarev , qemu-devel On 2012-05-09 16:48, Anthony Liguori wrote: > On 05/09/2012 02:34 PM, Jan Kiszka wrote: >> On 2012-05-09 16:27, Michael Tokarev wrote: >>> On 09.05.2012 23:21, Jan Kiszka wrote: >>>> On i386, glibc only saves/restores the signal mask via sigprocmask, >>>> excluding RT signal. A Linux bug in the compat version of this syscall >>>> corrupts the RT signal state, which will cause lockups of QEMU's VCPU >>>> threads. >>> >>> This should obviously be fixed in kernel, for benefit of all (not only >>> qemu), do you have any details here? >> >> compat_sys_sigprocmask reads 32-bit sigmask from user space, i.e. >> excluding RT signal, but calls sys_sigprocmask that takes a 64-bit >> sigset. So the RT signals are unblocked. I'm testing a simple patch ATM, >> will post it to LKML once this works. >> >>> >>>> Signed-off-by: Jan Kiszka >>>> --- >>>> >>>> I'm not sure where to fall back to. The existing code uses gthread, >>>> likely because it is the safer harbor. So I picked it as well. >>> >>> Can't we resort to the SIGUSR1 workaround for the time being, while >>> no RT signals are in actual use, and just have the time to let the >>> kernel side to fix the things up before some actual RTsig user will >>> emerge in qemu? I think it is a bit more conservative approach, >>> especially having in mind the minority of users this issue affects >>> (only 32/64 mixed environment). I'd favor for this variant, and >>> it looks like I'm the "main" 32/64bit user of qemu in this world :) >> >> Most conservative is definitely this patch, not switching to SIGUSR1, >> hoping that no other RT signal user shows up until current kernel are no >> longer in use. > > Sorry, how is using a totally different code path more conservative than using a > different signal number? If the gthread version is not safe to use, why do we fall back to it? > > Why would we even use an RT signal in the future? As both SIGUSR1 and 2 are now in use? Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux