From patchwork Thu Jul 16 01:00:21 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kamal Mostafa X-Patchwork-Id: 496065 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from huckleberry.canonical.com (huckleberry.canonical.com [91.189.94.19]) by ozlabs.org (Postfix) with ESMTP id DAC551401DA; Thu, 16 Jul 2015 11:01:42 +1000 (AEST) Received: from localhost ([127.0.0.1] helo=huckleberry.canonical.com) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1ZFXYQ-00031R-PV; Thu, 16 Jul 2015 01:01:38 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1ZFXXF-0002EO-5C for kernel-team@lists.ubuntu.com; Thu, 16 Jul 2015 01:00:25 +0000 Received: from 1.general.kamal.us.vpn ([10.172.68.52] helo=fourier) by youngberry.canonical.com with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.76) (envelope-from ) id 1ZFXXD-0005y2-UP; Thu, 16 Jul 2015 01:00:24 +0000 Received: from kamal by fourier with local (Exim 4.82) (envelope-from ) id 1ZFXXB-000059-NG; Wed, 15 Jul 2015 18:00:21 -0700 From: Kamal Mostafa To: Anton Blanchard Subject: [3.19.y-ckt stable] Patch "powerpc/perf: Fix book3s kernel to userspace backtraces" has been added to staging queue Date: Wed, 15 Jul 2015 18:00:21 -0700 Message-Id: <1437008421-32751-1-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.9.1 X-Extended-Stable: 3.19 Cc: Kamal Mostafa , kernel-team@lists.ubuntu.com X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.14 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: kernel-team-bounces@lists.ubuntu.com This is a note to let you know that I have just added a patch titled powerpc/perf: Fix book3s kernel to userspace backtraces to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue This patch is scheduled to be released in version 3.19.y-ckt4. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.19.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ------ From 8b5f9e3ebd431e9eb01fddfd8ccc917bd234ee6f Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Tue, 26 May 2015 15:10:24 +1000 Subject: powerpc/perf: Fix book3s kernel to userspace backtraces commit 72e349f1124a114435e599479c9b8d14bfd1ebcd upstream. When we take a PMU exception or a software event we call perf_read_regs(). This overloads regs->result with a boolean that describes if we should use the sampled instruction address register (SIAR) or the regs. If the exception is in kernel, we start with the kernel regs and backtrace through the kernel stack. At this point we switch to the userspace regs and backtrace the user stack with perf_callchain_user(). Unfortunately these regs have not got the perf_read_regs() treatment, so regs->result could be anything. If it is non zero, perf_instruction_pointer() decides to use the SIAR, and we get issues like this: 0.11% qemu-system-ppc [kernel.kallsyms] [k] _raw_spin_lock_irqsave | ---_raw_spin_lock_irqsave | |--52.35%-- 0 | | | |--46.39%-- __hrtimer_start_range_ns | | kvmppc_run_core | | kvmppc_vcpu_run_hv | | kvmppc_vcpu_run | | kvm_arch_vcpu_ioctl_run | | kvm_vcpu_ioctl | | do_vfs_ioctl | | sys_ioctl | | system_call | | | | | |--67.08%-- _raw_spin_lock_irqsave <--- hi mum | | | | | | | --100.00%-- 0x7e714 | | | 0x7e714 Notice the bogus _raw_spin_irqsave when we transition from kernel (system_call) to userspace (0x7e714). We inserted what was in the SIAR. Add a check in regs_use_siar() to check that the regs in question are from a PMU exception. With this fix the backtrace makes sense: 0.47% qemu-system-ppc [kernel.vmlinux] [k] _raw_spin_lock_irqsave | ---_raw_spin_lock_irqsave | |--53.83%-- 0 | | | |--44.73%-- hrtimer_try_to_cancel | | kvmppc_start_thread | | kvmppc_run_core | | kvmppc_vcpu_run_hv | | kvmppc_vcpu_run | | kvm_arch_vcpu_ioctl_run | | kvm_vcpu_ioctl | | do_vfs_ioctl | | sys_ioctl | | system_call | | __ioctl | | 0x7e714 | | 0x7e714 Signed-off-by: Anton Blanchard Signed-off-by: Michael Ellerman Signed-off-by: Kamal Mostafa --- arch/powerpc/perf/core-book3s.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) -- 1.9.1 diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c index 7c4f669..3cb25fd 100644 --- a/arch/powerpc/perf/core-book3s.c +++ b/arch/powerpc/perf/core-book3s.c @@ -131,7 +131,16 @@ static void pmao_restore_workaround(bool ebb) { } static bool regs_use_siar(struct pt_regs *regs) { - return !!regs->result; + /* + * When we take a performance monitor exception the regs are setup + * using perf_read_regs() which overloads some fields, in particular + * regs->result to tell us whether to use SIAR. + * + * However if the regs are from another exception, eg. a syscall, then + * they have not been setup using perf_read_regs() and so regs->result + * is something random. + */ + return ((TRAP(regs) == 0xf00) && regs->result); } /*