Commit 8520dedb authored Nov 06, 2014 by Daniel Thompson Committed by Steven Rostedt Nov 13, 2014

tracing: kdb: Fix kernel livelock with empty buffers

Currently kdb's ftdump command will livelock by constantly printk'ing
the empty string at KERN_EMERG level if it run when the ftrace system is
not in use. This occurs because trace_empty() never returns false when
the ring buffers are left at the start of a non-consuming read [launched
by ring_buffer_read_start()].

This patch changes the loop exit condition to use the result of
trace_find_next_entry_inc(). Effectively this switches the non-consuming
kdb dumper to follow the approach of the non-consuming userspace
interface [s_next()] rather than the consuming ftrace_dump().

Link: http://lkml.kernel.org/r/1415277716-19419-3-git-send-email-daniel.thompson@linaro.org



Cc: Ingo Molnar <mingo@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

parent c270cc75

kernel/trace/trace_kdb.c

+6 −6

Original line number	Diff line number	Diff line
		@@ -59,19 +59,19 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file)
		ring_buffer_read_start(iter.buffer_iter[cpu_file]);
		tracing_iter_reset(&iter, cpu_file);
		}
		if (!trace_empty(&iter))
		trace_find_next_entry_inc(&iter);
		while (!trace_empty(&iter)) {

		while (trace_find_next_entry_inc(&iter)) {
		if (!cnt)
		kdb_printf("---------------------------------\n");
		cnt++;

		if (trace_find_next_entry_inc(&iter) != NULL && !skip_lines)
		if (!skip_lines) {
		print_trace_line(&iter);
		if (!skip_lines)
		trace_printk_seq(&iter.seq);
		else
		} else {
		skip_lines--;
		}

		if (KDB_FLAG(CMD_INTERRUPT))
		goto out;
		}