Hi,

Here is the v9 of the series to improve backup instances of
the persistent ring buffer. The previous version is here:

https://lore.kernel.org/all/177071300558.2293046.12057922262682243630.stgit@mhiramat.tok.corp.google.com/

In this version, I removed bugfixes (those are actual fixes/minor
updates) and the force permission check in tracefs
because superuser can modify the permission by itself. Instead,
simply add read-only and FMODE_WRITE check in the related open()
file operations[1/3]. Also, I fixed 2 bugs in autoremove patch
to init dedicated workqueue correctly [2/3].

Series Description
------------------
Since backup instances are a kind of snapshot of the persistent
ring buffer, it should be readonly. And if it is readonly
there is no reason to keep it after reading all data via trace_pipe
because the data has been consumed. But user should be able to remove
the readonly instance by rmdir or truncating `trace` file.

Thus, [1/3] makes backup instances readonly (not able to write any
events, cleanup trace, change buffer size). Also, [2/3] removes the
backup instance after consuming all data via trace_pipe.
With this improvements, even if we makes a backup instance (using
the same amount of memory of the persistent ring buffer), it will
be removed after reading the data automatically.

Thanks,

---

Masami Hiramatsu (Google) (3):
      tracing: Make the backup instance non-reusable
      tracing: Remove the backup instance automatically after read
      tracing/Documentation: Add a section about backup instance


 Documentation/trace/debugging.rst |   19 ++++
 kernel/trace/trace.c              |  166 +++++++++++++++++++++++++++++--------
 kernel/trace/trace.h              |   13 +++
 kernel/trace/trace_boot.c         |    5 +
 kernel/trace/trace_events.c       |   76 ++++++++++-------
 5 files changed, 208 insertions(+), 71 deletions(-)

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>