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SubjectRe: [PATCH RFC v2] trace, blktrace: don't let the sysfs interface remove trace from running list

Jens (Cc'd) maintains the blktrace. He can take this if he wants.

-- Steve


On Mon, 10 Nov 2014 11:40:49 +0100
Arianna Avanzini <avanzini.arianna@gmail.com> 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 the trace from the
> running list, even if no function from the sysfs interface adds it to
> such a list. This leads to a null pointer dereference.
> This commit changes the blk_trace_remove_queue() function so that it
> does not remove the blk_trace from the running list.
>
> v2:
> - Now the patch removes the invocation of list_del() instead of
> adding an useless if branch, as suggested by Namhyung Kim.
>
> Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
> ---
> kernel/trace/blktrace.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index c1bd4ad..bd05fd2 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -1493,9 +1493,6 @@ 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);
> blk_trace_free(bt);
> return 0;
> }



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