tracing: Break out of tracing_wait_pipe() before wait_pipe() is called (f4874261) · Commits · 戴 / test

When reading from trace_pipe, if tracing is off but nothing was read it should block. If something is read and tracing is off, then EOF is returned. If tracing is on and there's nothing to read, it will block. But because the check of whether tracing is off and something was read is done after the block on the pipe, it is hit or miss if the EOF is returned or not leading to inconsistent behavior. Signed-off-by:

Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

+9 −9

Original line number	Diff line number	Diff line
		@@ -4237,15 +4237,6 @@ static int tracing_wait_pipe(struct file *filp)
		return -EAGAIN;
		}

		mutex_unlock(&iter->mutex);

		iter->trace->wait_pipe(iter);

		mutex_lock(&iter->mutex);

		if (signal_pending(current))
		return -EINTR;

		/*
		* We block until we read something and tracing is disabled.
		* We still block if tracing is disabled, but we have never
		@@ -4257,6 +4248,15 @@ static int tracing_wait_pipe(struct file *filp)
		*/
		if (!tracing_is_on() && iter->pos)
		break;

		mutex_unlock(&iter->mutex);

		iter->trace->wait_pipe(iter);

		mutex_lock(&iter->mutex);

		if (signal_pending(current))
		return -EINTR;
		}

		return 1;

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