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Tue, 11 Aug 2020 14:46:09 +0000 (GMT) From: Nathan Lynch To: Michael Ellerman , Michael Roth Subject: Re: [PATCH] powerpc/pseries/hotplug-cpu: increase wait time for vCPU death In-Reply-To: <87r1sd9z0d.fsf@mpe.ellerman.id.au> References: <20200804032937.7235-1-mdroth@linux.vnet.ibm.com> <873652zg8h.fsf@mpe.ellerman.id.au> <20200804161609.6cb2cb71@bahia.lan> <87zh79yen7.fsf@mpe.ellerman.id.au> <87mu37ylzu.fsf@linux.ibm.com> <159712434106.7191.15165087672426328577@sif> <87r1sd9z0d.fsf@mpe.ellerman.id.au> Date: Tue, 11 Aug 2020 09:46:08 -0500 Message-ID: <87ft8tz1e7.fsf@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-08-11_13:2020-08-11, 2020-08-11 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 bulkscore=0 mlxscore=0 adultscore=0 clxscore=1015 malwarescore=0 phishscore=0 priorityscore=1501 impostorscore=0 suspectscore=0 mlxlogscore=999 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2008110098 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@lists.ozlabs.org, Greg Kurz , Thiago Jung Bauermann , Cedric Le Goater Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Michael Ellerman writes: > Michael Roth writes: >> Quoting Nathan Lynch (2020-08-07 02:05:09) > ... >>> wait_for_cpu_stopped() should be able to accommodate a time-based >>> warning if necessary, but speaking as a likely recipient of any bug >>> reports that would arise here, I'm not convinced of the need and I >>> don't know what a good value would be. It's relatively easy to sample >>> the stack of a task that's apparently failing to make progress, plus I >>> probably would use 'perf probe' or similar to report the inputs and >>> outputs for the RTAS call. >> >> I think if we make the timeout sufficiently high like 2 minutes or so >> it wouldn't hurt and if we did seem them it would probably point to an >> actual bug. But I don't have a strong feeling either way. > > I think we should print a warning after 2 minutes. > > It's true that there are fairly easy mechanisms to work out where the > thread is stuck, but customers are unlikely to use them. They're just > going to report that it's stuck with no further info, and probably > reboot the machine before we get a chance to get any further info. > > Whereas if the kernel prints a warning with a stack trace we at least > have that to go on in an initial bug report. > >>> I'm happy to make this a proper submission after I can clean it up and >>> retest it, or Michael R. is welcome to appropriate it, assuming it's >>> acceptable. >>> >> >> I've given it a shot with this patch and it seems to be holding up in >> testing. If we don't think the ~2 minutes warning message is needed I >> can clean it up to post: >> >> https://github.com/mdroth/linux/commit/354b8c97bf0dc1146e36aa72273f5b33fe90d09e >> >> I'd likely break the refactoring patches out to a separate patch under >> Nathan's name since it fixes a separate bug potentially. > > While I like Nathan's refactoring, we probably want to do the minimal > fix first to ease backporting. > > Then do the refactoring on top of that. Fair enough, thanks.