From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-f177.google.com (mail-lb0-f177.google.com [209.85.217.177]) by kanga.kvack.org (Postfix) with ESMTP id 5CE1D6B00D8 for ; Sun, 24 May 2015 15:33:40 -0400 (EDT) Received: by lbbuc2 with SMTP id uc2so40688166lbb.2 for ; Sun, 24 May 2015 12:33:39 -0700 (PDT) Received: from mail-la0-f54.google.com (mail-la0-f54.google.com. [209.85.215.54]) by mx.google.com with ESMTPS id d4si6629350lbb.6.2015.05.24.12.33.37 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 24 May 2015 12:33:38 -0700 (PDT) Received: by labbd9 with SMTP id bd9so38710204lab.2 for ; Sun, 24 May 2015 12:33:37 -0700 (PDT) Date: Sun, 24 May 2015 21:34:04 +0200 From: Christoffer Dall Subject: [BUG] Read-Only THP causes stalls (commit 10359213d) Message-ID: <20150524193404.GD16910@cbox> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org, ebru.akagunduz@gmail.com Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, kirill.shutemov@linux.intel.com, riel@redhat.com, vbabka@suse.cz, zhangyanfei@cn.fujitsu.com, aarcange@redhat.com, Will Deacon , Andre Przywara , Marc Zyngier , linux-arm-kernel@lists.infradead.org Hi all, I noticed a regression on my arm64 APM X-Gene system a couple of weeks back. I would occassionally see the system lock up and see RCU stalls during the caching phase of kernbench. I then wrote a small script that does nothing but cache the files (http://paste.ubuntu.com/11324767/) and ran that in a loop. On a known bad commit (v4.1-rc2), out of 25 boots, I never saw it get past 21 iterations of the loop. I have since tried to run a bisect from v3.19 to v4.0 using 100 iterations as my criteria for a good commit. This resulted in the following first bad commit: 10359213d05acf804558bda7cc9b8422a828d1cd (mm: incorporate read-only pages into transparent huge pages, 2015-02-11) Indeed, running the workload on v4.1-rc4 still produced the behavior, but reverting the above commit gets me through 100 iterations of the loop. I have not tried to reproduce on an x86 system. Turning on a bunch of kernel debugging features *seems* to hide the problem. My config for the XGene system is defconfig + CONFIG_BRIDGE and CONFIG_POWER_RESET_XGENE. Please let me know if I can help test patches or other things I can do to help. I'm afraid that by simply reading the patch I didn't see anything obviously wrong with it which would cause this behavior. Thanks, -Christoffer -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org