From 9aba60fe6eb20453de53a572143bef22fa929fba Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Wed, 11 Mar 2009 19:52:30 -0400 Subject: [PATCH] tracing: fix trace_wait to know to wait on all cpus or just one Impact: fix to task live locking on reading trace_pipe on one CPU The same code is used for both trace_pipe (all CPUS) and the per_cpu trace_pipe file. When there is no data to read, it will check for signals and wait on the trace wait queue. The problem happens with the per_cpu wait. The trace_wait code checks all CPUs. Thus, if there's data in another CPU buffer, then it will exit the wait, without checking for signals or waiting on the wait queue. It would then try to read the empty buffer, and since that will just return nothing, then it will try to wait again. Unfortunately, that will again fail due to there still being data in the other buffers. This ends up with a live lock for the task. This patch fixes the trace_wait to be aware that the iterator may only be waiting on a single buffer. Signed-off-by: Steven Rostedt --- kernel/trace/trace.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 35ee63a..e60f4be 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -1666,6 +1666,19 @@ static int trace_empty(struct trace_iterator *iter) { int cpu; + /* If we are looking at one CPU buffer, only check that one */ + if (iter->cpu_file != TRACE_PIPE_ALL_CPU) { + cpu = iter->cpu_file; + if (iter->buffer_iter[cpu]) { + if (!ring_buffer_iter_empty(iter->buffer_iter[cpu])) + return 0; + } else { + if (!ring_buffer_empty_cpu(iter->tr->buffer, cpu)) + return 0; + } + return 1; + } + for_each_tracing_cpu(cpu) { if (iter->buffer_iter[cpu]) { if (!ring_buffer_iter_empty(iter->buffer_iter[cpu])) -- 2.7.4