From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Mon, 10 Apr 2017 17:40:22 +0200 From: Petr Mladek Subject: Re: [PATCH v5 01/15] stacktrace/x86: add function for detecting reliable stack traces Message-ID: <20170410154022.GC18673@pathway.suse.cz> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Archive: To: Josh Poimboeuf Cc: Jessica Yu , Jiri Kosina , Miroslav Benes , linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, Michael Ellerman , Heiko Carstens , x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, Vojtech Pavlik , Jiri Slaby , Chris J Arges , Andy Lutomirski , Ingo Molnar , Peter Zijlstra , Kamalesh Babulal , Balbir Singh List-ID: On Mon 2017-02-13 19:42:28, Josh Poimboeuf wrote: > For live patching and possibly other use cases, a stack trace is only > useful if it can be assured that it's completely reliable. Add a new > save_stack_trace_tsk_reliable() function to achieve that. > > Note that if the target task isn't the current task, and the target task > is allowed to run, then it could be writing the stack while the unwinder > is reading it, resulting in possible corruption. So the caller of > save_stack_trace_tsk_reliable() must ensure that the task is either > 'current' or inactive. > > save_stack_trace_tsk_reliable() relies on the x86 unwinder's detection > of pt_regs on the stack. If the pt_regs are not user-mode registers > from a syscall, then they indicate an in-kernel interrupt or exception > (e.g. preemption or a page fault), in which case the stack is considered > unreliable due to the nature of frame pointers. > > It also relies on the x86 unwinder's detection of other issues, such as: > > - corrupted stack data > - stack grows the wrong way > - stack walk doesn't reach the bottom > - user didn't provide a large enough entries array > > Such issues are reported by checking unwind_error() and !unwind_done(). > > Also add CONFIG_HAVE_RELIABLE_STACKTRACE so arch-independent code can > determine at build time whether the function is implemented. > > Signed-off-by: Josh Poimboeuf Just for record, this version looks fine to me: Reviewed-by: Petr Mladek Best Regards, Petr PS: I was on the sick leave longer then expected. The patch set has been pushed into the for-4.12 branch in jikos/livepatching.git in the meantime. I check it there just for completeness. You do not need to add my Reviewed-by tags.