From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751495AbeEVHYQ (ORCPT ); Tue, 22 May 2018 03:24:16 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:51220 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751106AbeEVHYH (ORCPT ); Tue, 22 May 2018 03:24:07 -0400 From: Vaibhav Jain To: Michal Suchanek , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Balbir Singh , Nicholas Piggin , Breno Leitao , "Naveen N. Rao" , "Guilherme G. Piccoli" , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Cc: Michal Suchanek Subject: Re: [PATCH] powerpc/xmon: really enable xmon when a breakpoint is set In-Reply-To: <20180521132108.7938-1-msuchanek@suse.de> References: <20180521132108.7938-1-msuchanek@suse.de> Date: Tue, 22 May 2018 12:53:53 +0530 MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 x-cbid: 18052207-0044-0000-0000-000005550CC6 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18052207-0045-0000-0000-00002896986A Message-Id: <87bmd8xieu.fsf@vajain21.in.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-05-22_01:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1805220088 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thanks for the patch Michal, Michal Suchanek writes: > When single-stepping kernel code from xmon without a debug hook enabled > the kernel crashes. This can happen when kernel starts with xmon on > crash disabled but xmon is entered using sysrq. > > Commit e1368d0c9edb ("powerpc/xmon: Setup debugger hooks when first > break-point is set") adds force_enable_xmon function that prints > "xmon: Enabling debugger hooks" but does not enable them. Debugger hooks are enabled just befores debugger() is entered from sysrq_handle_xmon(). Thats why force_enable_xmon() simply sets sets 'xmon_on=1' and exits. The problem you are seeing is probably due to sysrq_handle_xmon() clearing the debugger hooks on return from debugger() as xmon_on was never set for the 's' xmon command. > Add the call to xmon_init to install the debugger hooks in > force_enable_xmon and also call force_enable_xmon when single-stepping > in xmon. Only calling force_enable_xmon() from do_step() should be suffice as on exit from the debugger() the value of xmon_on is checked and if required the debugger hooks are kept instead of getting cleared. > arch/powerpc/xmon/xmon.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c > index a0842f1ff72c..504bd1c3d8b0 100644 > --- a/arch/powerpc/xmon/xmon.c > +++ b/arch/powerpc/xmon/xmon.c > @@ -1275,6 +1279,7 @@ static inline void force_enable_xmon(void) > if (!xmon_on) { > printf("xmon: Enabling debugger hooks\n"); > xmon_on = 1; > + xmon_init(1); > } > } As mentioned above call to force_enable_xmon() is usually done in context of sysrq_handle_xmon() which sets the debugger hooks as soon as its entered. So I think that this hunk is not really needed. -- Vaibhav Jain Linux Technology Center, IBM India Pvt. Ltd.