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Fri, 28 Jan 2022 16:17:33 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A1525AE055; Fri, 28 Jan 2022 16:17:33 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2D677AE045; Fri, 28 Jan 2022 16:17:33 +0000 (GMT) Received: from tuxmaker.linux.ibm.com (unknown [9.152.85.9]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTPS; Fri, 28 Jan 2022 16:17:33 +0000 (GMT) From: Sven Schnelle To: Mark Rutland Subject: Re: ftrace hangs waiting for rcu References: <20220127114249.03b1b52b@gandalf.local.home> Date: Fri, 28 Jan 2022 17:17:32 +0100 In-Reply-To: (Mark Rutland's message of "Fri, 28 Jan 2022 16:11:57 +0000") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 X-Proofpoint-GUID: u8O8FusVp6nn3H4y_5Ekm_czzhxm816Q X-Proofpoint-ORIG-GUID: jYcgQy5HdrGbbLk3NI1FNR-A0FeeLH0u X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.816,Hydra:6.0.425,FMLib:17.11.62.513 definitions=2022-01-28_05,2022-01-28_01,2021-12-02_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=948 lowpriorityscore=0 malwarescore=0 adultscore=0 impostorscore=0 suspectscore=0 spamscore=0 priorityscore=1501 mlxscore=0 clxscore=1015 phishscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2201110000 definitions=main-2201280101 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: linux-s390@vger.kernel.org, Kees Cook , "Paul E. McKenney" , hca@linux.ibm.com, LKML , Steven Rostedt , Ingo Molnar , Sachin Sant , Russell King , Andrew Morton , Yinan Liu , linuxppc-dev@lists.ozlabs.org, Ard Biesheuvel , linux-arm-kernel@lists.infradead.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hi Mark, Mark Rutland writes: > On Fri, Jan 28, 2022 at 05:08:48PM +0100, Sven Schnelle wrote: >> We noticed the PR from Paul and are currently testing the fix. So far >> it's looking good. The configuration where we have seen the hang is a >> bit unusual: >> >> - 16 physical CPUs on the kvm host >> - 248 logical CPUs inside kvm > > Aha! 248 is notably *NOT* a power of two, and in this case the shift would be > wrong (ilog2() would give 7, when we need a shift of 8). > > So I suspect you're hitting the same issue as I was. Argh, indeed! I somehow changed 'power of two' to 'odd number' in my head. I guess it's time for the weekend. :-) Thanks!