Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753190Ab0AYWLN (ORCPT ); Mon, 25 Jan 2010 17:11:13 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752021Ab0AYWLM (ORCPT ); Mon, 25 Jan 2010 17:11:12 -0500 Received: from mail-fx0-f220.google.com ([209.85.220.220]:53948 "EHLO mail-fx0-f220.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751067Ab0AYWLH (ORCPT ); Mon, 25 Jan 2010 17:11:07 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=rauft5UBX55mRW1OFh8b5mi7pWIKqPvQt51AlJxvba1YWPUyWx+TBm5tbAoSAvsVDb L5ve/f4JtthFl3Oatt41suKHqIETgip6gt7UjsKh1AjNwrH//73oXkJPb6YtaiH4GZ6R 9wXTBSLwS3sMn7Rb4TlZMjgiFQ9Bq+DutWNb0= Date: Mon, 25 Jan 2010 23:11:04 +0100 From: Frederic Weisbecker To: "K.Prasad" Cc: LKML , Ingo Molnar , Alan Stern Subject: Re: [RFC Patch 2/2][Bugfix][x86][hw-breakpoint] Fix return-code to notifier chain in hw_breakpoint_handler Message-ID: <20100125221101.GE5087@nowhere> References: <20091226175533.149765731@linux.vnet.ibm.com> <20091226182833.GC9494@in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091226182833.GC9494@in.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2536 Lines: 84 On Sat, Dec 26, 2009 at 11:58:33PM +0530, K.Prasad wrote: > The hw-breakpoint handler will return NOTIFY_DONE for user-space breakpoints > to generate SIGTRAP signal (and not for kernel-space addresses). Please tell a bit more in your changelogs. It took me some time to guess whether this is a fix or not. And this is not a fix but an optimization because SIGTRAP is only sent if needed. Here is what happens in do_debug() after handling the breakpoint: if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS)) send_sigtrap(tsk, regs, error_code, si_code); This can only happen if we took the ptrace handler path. Also: > Signed-off-by: K.Prasad > --- > arch/x86/kernel/hw_breakpoint.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > Index: linux-2.6-tip/arch/x86/kernel/hw_breakpoint.c > =================================================================== > --- linux-2.6-tip.orig/arch/x86/kernel/hw_breakpoint.c > +++ linux-2.6-tip/arch/x86/kernel/hw_breakpoint.c > @@ -502,8 +502,6 @@ static int __kprobes hw_breakpoint_handl > rcu_read_lock(); > > bp = per_cpu(bp_per_reg[i], cpu); > - if (bp) > - rc = NOTIFY_DONE; > /* > * Reset the 'i'th TRAP bit in dr6 to denote completion of > * exception handling > @@ -517,6 +515,13 @@ static int __kprobes hw_breakpoint_handl > rcu_read_unlock(); > break; > } > + /* > + * Further processing in do_debug() is needed for a) user-space > + * breakpoints (to generate signals) and b) when the system has > + * taken exception due to multiple causes > + */ > + if (bp->attr.bp_addr < TASK_SIZE) > + rc = NOTIFY_DONE; Is that < TASK_SIZE an accurate check? We want support for userspace breakpoints on perf tools later, and those don't want signals. We do this cleanup in the beginning of the breakpoint handler: current->thread.debugreg6 &= ~DR_TRAP_BITS; And from ptrace.c:ptrace_triggered(): thread->debugreg6 |= (DR_TRAP0 << i); This is called on perf_bp_event(). Instead of checking if this is a userspace thread, we should actually check if this is a ptrace breakpoint by looking at this in the end of hw_breakpoint_handler(). current->thread.debugreg6 & DR_TRAP_BITS Only ptrace breakpoints require signals. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/