lkml.org 
[lkml]   [2014]   [Nov]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH RFC] trace, blktrace: remove trace from running list only if trace is running
Date
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 <avanzini.arianna@gmail.com>
> ---
> 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;
> }


\
 
 \ /
  Last update: 2014-11-10 10:01    [W:0.079 / U:3.000 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site