Date: Tue, 10 Apr 2018 21:06:03 +0000 From: Dexuan Cui <decui@microsoft.com> To: Bruce Evans <brde@optusnet.com.au> Cc: "jeff@freebsd.org" <jeff@freebsd.org>, "bugs@freebsd.org" <bugs@freebsd.org>, "Hongxiong Xian (Wicresoft)" <v-hoxian@microsoft.com> Subject: RE: [Bug 227404] UP FreeBSD VM always hangs on reboot since 20180329-r331740 Message-ID: <KL1P15301MB00064D2EE232ACE131D1A85ABFBE0@KL1P15301MB0006.APCP153.PROD.OUTLOOK.COM> In-Reply-To: <20180411055306.P5336@besplex.bde.org> References: <bug-227404-39@https.bugs.freebsd.org/bugzilla/> <bug-227404-39-TxuoE7IXT0@https.bugs.freebsd.org/bugzilla/> <20180410173347.D1459@besplex.bde.org> <SG2P15301MB0015EA97582E940755361F64BFBE0@SG2P15301MB0015.APCP153.PROD.OUTLOOK.COM> <20180411055306.P5336@besplex.bde.org>
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> From: Bruce Evans <brde@optusnet.com.au> > Sent: Tuesday, April 10, 2018 13:09 > > Here the bug is that UP FreeBSD VM hangs on reboot or power-off, and > > I'm sure this recent patch (which was committed by Jeff on Mar 26) caus= ed > > this bug: > > r331561:Fix a bug introduced in r329612 that slowly invalidates all cle= an bufs. > > > > However, SMP VM with 2 or more CPUs doesn't hang on reboot/power-off > > according to our tests. >=20 > Actually, r329612 is what causes this bug. I already did the bisection > to find almost this bug a couple of weeks ago. The hang occurs on amd64 > with 4 CPUs but not on amd64 with 8 CPUs or i386 with 4 or 8 CPUS. I > just checked that it occurs on i386 with 1 CPU. All on the same machine. > But r329611 doesn't hang for any of these cases. So, it looks to me that: r329612 introduced a hang issue, so Jeff made r331= 561, trying to fix the issue, but it looks the issue is not completely fixed (at= least for me). I didn't test r329612. We noticed our amd64 VM (which has a single CPU) hung . The VM kernel was=20 built with yesterday's latest kernel code + the default GENERIC kernel conf= ig. However, using the same kernel binary, if we configure 2 or more CPUs to the VM, the VM doesn't hang on reboot. If I use the latest code but manually remove the changes made by r331561,=20 the hang issue with our single-CPU VM will go away. I hope the info is helpful. =20 > I still think there is an older bug, but now think it is related. I > only tested with SCHED_4BSD. For SCHED_4BSD, I suspect that the bug > is from pinning a thread to a CPU and then stopping that CPU. Pure > UP has no problems since pinning is null for it. SCHED_4BSD has especial= ly > special handing for SMP (a separate runq for each CPU. I have been > modifying > SCHED_4BSD and the separate queues mostly get in the way). >=20 > Bruce I always use the default GENERIC kernel options, so I guess I'm using SCHED= _4BSD(?).. Thanks, -- Dexuan
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