Re: [PATCH] tracing/mmiotrace: fix resource leak on trace_pipe close

[Steven Rostedt]

On Wed, 15 Jul 2026 20:06:04 +0530
deepakraog <gaikwad.dcg@xxxxxxxxx> wrote:

> mmio_pipe_open() allocates a header_iter and takes a pci_dev reference
> when trace_pipe is opened. mmio_close() frees them, but it was only
> wired to the tracer's .close callback.

Were you able to trigger a kmemleak?

> 
> tracing_release_pipe() invokes .pipe_close, not .close, when the
> trace_pipe file is released. As a result, closing trace_pipe with the
> mmiotrace tracer active leaked the header_iter allocation and left a
> stale pci_dev reference.

It would be good if you showed how a leak can happen, as the mmio_read()
does clean up the descriptor, making the above statement incorrect.

> 
> Set .pipe_close to mmio_close, matching how function_graph wires both
> callbacks to the same handler.
> 


The mmio_read() will free up the descriptor if you read the trace_pipe file
until it blocks. But reading part of it may trigger the leak. Such as:

  # head -n 1 /sys/kernel/tracing/trace_pipe 
 head: /sys/kernel/tracing/trace_pipe: cannot seek to relative offset 0: Illegal seek
 VERSION 20070824

and running that over and over again will produce a leak caught by kmemleak.

I'll update the change log.

-- Steve