Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751543AbdISKAx (ORCPT ); Tue, 19 Sep 2017 06:00:53 -0400 Received: from ozlabs.org ([103.22.144.67]:52007 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750823AbdISKAw (ORCPT ); Tue, 19 Sep 2017 06:00:52 -0400 From: Michael Ellerman To: Ravi Bangoria , linuxppc-dev@lists.ozlabs.org Cc: benh@kernel.crashing.org, paulus@samba.org, maddy@linux.vnet.ibm.com, tglx@linutronix.de, mingo@kernel.org, kan.liang@intel.com, linux-kernel@vger.kernel.org, Ravi Bangoria Subject: Re: [PATCH] powerpc/sysrq: Fix oops whem ppmu is not registered In-Reply-To: <1505801826-12396-1-git-send-email-ravi.bangoria@linux.vnet.ibm.com> References: <1505801826-12396-1-git-send-email-ravi.bangoria@linux.vnet.ibm.com> User-Agent: Notmuch/0.21 (https://notmuchmail.org) Date: Tue, 19 Sep 2017 20:00:49 +1000 Message-ID: <87wp4vknxq.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 931 Lines: 30 Ravi Bangoria writes: > Kernel crashes if power pmu is not registered and user tries to dump > regs with 'echo p > /proc/sysrq-trigger'. Sample log: > > Unable to handle kernel paging request for data at address 0x00000008 > Faulting instruction address: 0xc0000000000d52f0 > > NIP [c0000000000d52f0] perf_event_print_debug+0x10/0x230 > LR [c00000000058a938] sysrq_handle_showregs+0x38/0x50 > Call Trace: > printk+0x38/0x4c (unreliable) > __handle_sysrq+0xe4/0x270 > write_sysrq_trigger+0x64/0x80 > proc_reg_write+0x80/0xd0 > __vfs_write+0x40/0x200 > vfs_write+0xc8/0x240 > SyS_write+0x60/0x110 > system_call+0x58/0x6c Thanks. I added: Fixes: 5f6d0380c640 ("powerpc/perf: Define perf_event_print_debug() to print PMU register values") But I don't think I'll Cc stable, I can't think why we'd ever *not* have a ppmu registered. How did you hit it? cheers