From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751569Ab1BNR5y (ORCPT ); Mon, 14 Feb 2011 12:57:54 -0500 Received: from mail-bw0-f46.google.com ([209.85.214.46]:62430 "EHLO mail-bw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750866Ab1BNR5w convert rfc822-to-8bit (ORCPT ); Mon, 14 Feb 2011 12:57:52 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type:content-transfer-encoding; b=htvIbo1K/B8mk6HSgbKS9/ITJg6GHDKOYWpcDKqEro2za217Kr15r6d+W1/R8J9vcV ObBctHn+fd+u7dCLEp0A6An0A4tjV48/7SHAItznW4q7fVEAA4M6We8nUWc8gttD2Szn U/r+QFixFbuQ4K9sVAoUyPQ54frJEdLvYS+OE= MIME-Version: 1.0 In-Reply-To: <20110214173910.GA15847@redhat.com> References: <20110204105343.GA12133@htj.dyndns.org> <20110207174821.GA1237@redhat.com> <20110209141803.GH3770@htj.dyndns.org> <201102132325.55353.vda.linux@googlemail.com> <20110214153149.GB8761@redhat.com> <20110214173910.GA15847@redhat.com> From: Denys Vlasenko Date: Mon, 14 Feb 2011 18:57:31 +0100 Message-ID: Subject: Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after PTRACE_ATTACH To: Oleg Nesterov Cc: Tejun Heo , Roland McGrath , jan.kratochvil@redhat.com, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 14, 2011 at 6:39 PM, Oleg Nesterov wrote: > On 02/14, Denys Vlasenko wrote: >> >> On Mon, Feb 14, 2011 at 4:31 PM, Oleg Nesterov wrote: >> > On 02/13, Denys Vlasenko wrote: >> >> >> >> $ strace -tt sleep 30 >> >> 23:02:15.619262 execve("/bin/sleep", ["sleep", "30"], [/* 30 vars */]) = 0 >> >> ... >> >> 23:02:15.622112 nanosleep({30, 0}, NULL) = ? ERESTART_RESTARTBLOCK (To be restarted) >> >> 23:02:23.781165 --- SIGSTOP (Stopped (signal)) @ 0 (0) --- >> >> 23:02:23.781251 --- SIGSTOP (Stopped (signal)) @ 0 (0) --- >> >>     (I forgot again why we see it twice. Another quirk I guess...) >> > >> >      (this is correct, the tracee reports the signal=SIGSTOP, then >> >       it reports it actually stopps with exit_code=SIGSTOP) >> >> Ah, I see. Is there any way debugger can distinguish between these two >> different stops? > > IIRC, the (only?) way to distinguish is to check last_siginfo != NULL > via ptrace(PTRACE_GETSIGINFO). What do you think strace needs to do when it sees second SIGSTOP (meaning "in theory", not "on current kernel which may be buggy")? ptrace(PTRACE_SYSCALL, $PID, 0x1, 0)? nothing? something else? -- vda