Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752044AbaKJIZ7 (ORCPT ); Mon, 10 Nov 2014 03:25:59 -0500 Received: from lgeamrelo02.lge.com ([156.147.1.126]:56104 "EHLO lgeamrelo02.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751759AbaKJIZ6 (ORCPT ); Mon, 10 Nov 2014 03:25:58 -0500 X-Original-SENDERIP: 10.177.222.235 X-Original-MAILFROM: namhyung@gmail.com From: Namhyung Kim To: Arianna Avanzini Cc: rostedt@goodmis.org, mingo@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC] trace, blktrace: remove trace from running list only if trace is running References: <1415459680-1749-1-git-send-email-avanzini.arianna@gmail.com> Date: Mon, 10 Nov 2014 17:25:56 +0900 In-Reply-To: <1415459680-1749-1-git-send-email-avanzini.arianna@gmail.com> (Arianna Avanzini's message of "Sat, 8 Nov 2014 16:14:40 +0100") Message-ID: <8761env4vf.fsf@sejong.aot.lge.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Arianna, On Sat, 8 Nov 2014 16:14:40 +0100, Arianna Avanzini wrote: > Currently, blktrace can be started/stopped via its ioctl-based interface > (used by the userspace blktrace tool) or via its ftrace interface. The > function blk_trace_remove_queue(), called each time an "enable" tunable > of the ftrace interface transitions to zero, removes unconditionally the > trace from the running list, even if its state is not Blktrace_running. > In fact, the state of a blk_trace is modified only by the ioctl-based > interface, and a blk_trace is added to the running list only when its > state transitions from Blktrace_setup or Blktrace_stopped to > Blktrace_running. If the ioctl-based interface is not being used, the > state of the blk_trace is undefined. > In this case, using the sysfs tunable to stop a trace would trigger a > removal of a blk_trace from the running list while it is not on such a > list, leading to a null pointer dereference. This commit attempts to fix > the issue by letting the blk_trace_remove_queue() function remove the > blk_trace from the running list only if its state is Blktrace_running. What about just getting rid of the list_del()? blk_trace_setup_queue() doesn't add it to running_trace_list and I think we should prevent mix of ioctl and sysfs usage somehow.. Thanks, Namhyung > > Signed-off-by: Arianna Avanzini > --- > kernel/trace/blktrace.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c > index c1bd4ad..f58b617 100644 > --- a/kernel/trace/blktrace.c > +++ b/kernel/trace/blktrace.c > @@ -1493,9 +1493,11 @@ static int blk_trace_remove_queue(struct request_queue *q) > if (atomic_dec_and_test(&blk_probes_ref)) > blk_unregister_tracepoints(); > > - spin_lock_irq(&running_trace_lock); > - list_del(&bt->running_list); > - spin_unlock_irq(&running_trace_lock); > + if (bt->trace_state == Blktrace_running) { > + spin_lock_irq(&running_trace_lock); > + list_del(&bt->running_list); > + spin_unlock_irq(&running_trace_lock); > + } > blk_trace_free(bt); > return 0; > } -- 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/