From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751247AbeCHVnv (ORCPT ); Thu, 8 Mar 2018 16:43:51 -0500 Received: from mail-pf0-f195.google.com ([209.85.192.195]:45436 "EHLO mail-pf0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750792AbeCHVnt (ORCPT ); Thu, 8 Mar 2018 16:43:49 -0500 X-Google-Smtp-Source: AG47ELtsAtvbgn+siClIrXgLt84Ro65O63ij7vzr8tFM/IBOWZEK/hu+Rvqcc+3D5l9zwoVRFNQUNg== Date: Fri, 9 Mar 2018 08:43:33 +1100 From: Balbir Singh To: Torsten Duwe Cc: Miroslav Benes , Michael Ellerman , Jiri Kosina , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, live-patching@vger.kernel.org Subject: Re: [PATCH 2/2] ppc64le save_stack_trace_tsk_reliable (Was: HAVE_RELIABLE_STACKTRACE) Message-ID: <20180309084333.23287074@gmail.com> In-Reply-To: <20180227160924.GA19111@lst.de> References: <20171004152516.25803-1-kamalesh@linux.vnet.ibm.com> <20171005124313.GA25100@lst.de> <9f388c9a-8d74-865a-b113-f77322918b39@linux.vnet.ibm.com> <20171017144733.GB2136@lst.de> <95e6f942-88b7-0208-0eb0-2f5462aec410@linux.vnet.ibm.com> <20171020120739.GA20306@lst.de> <1508547548.5662.2.camel@gmail.com> <39bb7180-1adf-4df6-c9ba-c6f92754767f@linux.vnet.ibm.com> <20171212113912.GA1907@lst.de> <20180227160924.GA19111@lst.de> X-Mailer: Claws Mail 3.15.1-dirty (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 27 Feb 2018 17:09:24 +0100 Torsten Duwe wrote: > On Tue, Dec 12, 2017 at 01:12:37PM +0100, Miroslav Benes wrote: > > > > I think that this is not enough. You need to also implement > > save_stack_trace_tsk_reliable() for powerpc defined as __weak in > > kernel/stacktrace.c. > > So here is my initial proposal. I'd really like to get the successful > exit stricter, i.e. hit the initial stack value exactly instead of just > a window. Also, the check for kernel code looks clumsy IMHO. IOW: > Comments more than welcome! > > Most of it is Copy&Waste, nonetheless: :) > > Signed-off-by: Torsten Duwe > > > diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c > index d534ed901538..e08af49e71d0 100644 > --- a/arch/powerpc/kernel/stacktrace.c > +++ b/arch/powerpc/kernel/stacktrace.c > @@ -13,6 +13,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -76,3 +77,58 @@ save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace) > save_context_stack(trace, regs->gpr[1], current, 0); > } > EXPORT_SYMBOL_GPL(save_stack_trace_regs); > + > +#ifdef CONFIG_HAVE_RELIABLE_STACKTRACE > +int > +save_stack_trace_tsk_reliable(struct task_struct *tsk, > + struct stack_trace *trace) Just double checking this is called under the task_rq_lock, so its safe to call task_stack_page() as opposed to try_get_task_stack() > +{ > + unsigned long sp; > + unsigned long stack_page = (unsigned long)task_stack_page(tsk); > + /* the last frame (unwinding first) may not yet have saved its LR onto the stack. */ > + int firstframe = 1; > + > + if (tsk == current) > + sp = current_stack_pointer(); > + else > + sp = tsk->thread.ksp; > + > + if (sp < stack_page + sizeof(struct thread_struct) > + || sp > stack_page + THREAD_SIZE - STACK_FRAME_OVERHEAD) > + return 1; Some of this is already present in validate_sp(), it also validates irq stacks, should we just reuse that? > + > + for (;;) { > + unsigned long *stack = (unsigned long *) sp; > + unsigned long newsp, ip; > + > + newsp = stack[0]; > + /* Stack grows downwards; unwinder may only go up */ > + if (newsp <= sp) > + return 1; > + > + if (newsp >= stack_page + THREAD_SIZE) > + return 1; /* invalid backlink, too far up! */ > + > + /* Examine the saved LR: it must point into kernel code. */ > + ip = stack[STACK_FRAME_LR_SAVE]; > + if ( (ip & 0xEFFF000000000000) != CONFIG_KERNEL_START > + && !firstframe) > + return 1; > + firstframe = 0; > + > + if (!trace->skip) > + trace->entries[trace->nr_entries++] = ip; > + else > + trace->skip--; > + > + if (newsp > stack_page + THREAD_SIZE - STACK_FRAME_OVERHEAD) > + break; /* hit the window for last frame */ > + > + if (trace->nr_entries >= trace->max_entries) > + return -E2BIG; > + > + sp = newsp; > + } > + return 0; > +} > +#endif /* CONFIG_HAVE_RELIABLE_STACKTRACE */ > Looks good to me otherwise. Acked-by: Balbir Singh