From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id C8BB76B002D for ; Mon, 24 Oct 2011 10:46:18 -0400 (EDT) Date: Mon, 24 Oct 2011 16:41:27 +0200 From: Oleg Nesterov Subject: Re: [PATCH 13/X] uprobes: introduce UTASK_SSTEP_TRAPPED logic Message-ID: <20111024144127.GA14975@redhat.com> References: <20110920115938.25326.93059.sendpatchset@srdronam.in.ibm.com> <20111015190007.GA30243@redhat.com> <20111019215139.GA16395@redhat.com> <20111019215344.GG16395@redhat.com> <20111022072030.GB24475@in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111022072030.GB24475@in.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Ananth N Mavinakayanahalli Cc: Srikar Dronamraju , Peter Zijlstra , Ingo Molnar , Steven Rostedt , Linux-mm , Arnaldo Carvalho de Melo , Linus Torvalds , Jonathan Corbet , Masami Hiramatsu , Hugh Dickins , Christoph Hellwig , Thomas Gleixner , Andi Kleen , Andrew Morton , Jim Keniston , Roland McGrath , LKML On 10/22, Ananth N Mavinakayanahalli wrote: > > On Wed, Oct 19, 2011 at 11:53:44PM +0200, Oleg Nesterov wrote: > > Finally, add UTASK_SSTEP_TRAPPED state/code to handle the case when > > xol insn itself triggers the signal. > > > > In this case we should restart the original insn even if the task is > > already SIGKILL'ed (say, the coredump should report the correct ip). > > This is even more important if the task has a handler for SIGSEGV/etc, > > The _same_ instruction should be repeated again after return from the > > signal handler, and SSTEP can never finish in this case. > > Oleg, > > Not sure I understand this completely... I hope you do not think I do ;) > When you say 'correct ip' you mean the original vaddr where we now have > a uprobe breakpoint and not the xol copy, right? Yes, > Coredump needs to report the correct ip, but should it also not report > correctly the instruction that caused the signal? Ergo, shouldn't we > put the original instruction back at the uprobed vaddr? OK, now I see what you mean. I was confused by the "restore the original instruction before _restart_" suggestion. Agreed! it would be nice to "hide" these int3's if we dump the core, but I think this is a bit off-topic. It makes sense to do this in any case, even if the core-dumping was triggered by another thread/insn. It makes sense to remove all int3's, not only at regs->ip location. But how can we do this? This is nontrivial. And. Even worse. Suppose that you do "gdb probed_application". Now you see int3's in the disassemble output. What can we do? I think we can do nothing, at least currently. This just reflects the fact that uprobe connects to inode, not to process/mm/etc. What do you think? Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org