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.
Signed-off-by: Arianna Avanzini <[email protected]> --- 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; } -- 2.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
