tree 7568cd26fbcc3f64168a73a1929088df42c57701
parent a9fcaaac37b3baba1343f906f52aeb65c4d4e356
author Steven Rostedt (Red Hat) <rostedt@goodmis.org> 1402407960 -0400
committer Steven Rostedt <rostedt@goodmis.org> 1402407960 -0400

ring-buffer: Check if buffer exists before polling

The per_cpu buffers are created one per possible CPU. But these do
not mean that those CPUs are online, nor do they even exist.

With the addition of the ring buffer polling, it assumes that the
caller polls on an existing buffer. But this is not the case if
the user reads trace_pipe from a CPU that does not exist, and this
causes the kernel to crash.

Simple fix is to check the cpu against buffer bitmask against to see
if the buffer was allocated or not and return -ENODEV if it is
not.

More updates were done to pass the -ENODEV back up to userspace.

Link: http://lkml.kernel.org/r/5393DB61.6060707@oracle.com

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Cc: stable@vger.kernel.org # 3.10+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>