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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>
This commit is contained in:
Daniel Thompson 2014-11-06 12:41:56 +00:00 committed by Steven Rostedt
parent c270cc75cd
commit 8520dedbbf
1 changed files with 6 additions and 6 deletions
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12
kernel/trace/trace_kdb.c
View File

@ -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;
}