From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 4F761DE03D for ; Fri, 2 May 2008 02:33:49 +1000 (EST) Message-Id: <78125A27-D99A-447D-9C65-4705DD153567@kernel.crashing.org> From: Kumar Gala To: Scott Wood In-Reply-To: <20080501161451.GH17142@ld0162-tx32.am.freescale.net> Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes Mime-Version: 1.0 (Apple Message framework v919.2) Subject: Re: [PATCH] [POWERPC] Rework EXC_LEVEL_EXCEPTION_PROLOG code Date: Thu, 1 May 2008 11:33:34 -0500 References: <1209592495.18023.246.camel@pasglop> <12ECF63E-7CEA-48FD-9447-7D534C29271D@kernel.crashing.org> <18457.1279.401197.763726@cargo.ozlabs.ibm.com> <18457.32297.485053.356477@cargo.ozlabs.ibm.com> <2DF41779-732B-4477-9DAC-147CDC5C9885@kernel.crashing.org> <20080501161451.GH17142@ld0162-tx32.am.freescale.net> Cc: linuxppc-dev@ozlabs.org, Paul Mackerras List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On May 1, 2008, at 11:14 AM, Scott Wood wrote: > On Thu, May 01, 2008 at 08:17:07AM -0500, Kumar Gala wrote: >> On May 1, 2008, at 3:24 AM, Paul Mackerras wrote: >>> The most common cases are (a) something that ultimately generates >>> input on a tty (e.g. a character arriving on a serial port) and that >>> input turns out to be a ^C or similar, or (b) something that signals >>> I/O completion and the program doing the I/O has requested >>> notification by a SIGIO. But in general any driver code can send a >>> signal to userspace if it wants. > > And, of course, SIGALRM and similar timer mechanisms. > >> ok. Was just wondering how the async exception know that the signal >> it wanted to send belonged to the particular process that is running. >> But I guess there are cases that the signal is really intended for >> who >> ever is currently running? > > No, it knows based on its own data structures who it's intended for -- > and sometimes that happens to be the currently running process. Let me ask the question differently. Are there cases that some event occurs in the system and a signal is delivered to the current process regardless of what that process is. I'm guessing so, based on the tty example. So for the specific case I'm looking at (kprobes & debug exceptions from kernel space), I think its reasonable to BUG_ON() if thread_info- >flags changes such that TIF_SIGPENDING or TIF_NEED_RESCHED get set we aren't from user-space. - k