Messages in this thread | | | Date | Mon, 10 Nov 2014 11:40:32 +0100 | From | Arianna Avanzini <> | Subject | Re: [PATCH RFC] trace, blktrace: remove trace from running list only if trace is running |
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On Mon, Nov 10, 2014 at 05:25:56PM +0900, Namhyung Kim wrote: > Hi Arianna,
Hi Namhyung,
thank you for replying.
> > 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.. >
And blk_trace_remove_queue() is used only by the sysfs interface, you're right. I'm re-sending the patch with your comment applied.
Thank you, Arianna
> 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; > > }
-- /* * Arianna Avanzini * avanzini.arianna@gmail.com * http://ava.webhop.me */
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