353cc21937
The function ring_buffer_subbuf_order_set() just updated the sub-buffers to the new size, but this also changes the size of the buffer in doing so. As the size is determined by nr_pages * subbuf_size. If the subbuf_size is increased without decreasing the nr_pages, this causes the total size of the buffer to increase. This broke the latency tracers as the snapshot needs to be the same size as the main buffer. The size of the snapshot buffer is only expanded when needed, and because the order is still the same, the size becomes out of sync with the main buffer, as the main buffer increased in size without the tracing system knowing. Calculate the nr_pages to allocate with the new subbuf_size to be buffer_size / new_subbuf_size. Link: https://lore.kernel.org/linux-trace-kernel/20231219185630.649397785@goodmis.org Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Tzvetomir Stoyanov <tz.stoyanov@gmail.com> Cc: Vincent Donnefort <vdonnefort@google.com> Cc: Kent Overstreet <kent.overstreet@gmail.com> Fixes: f9b94daa542a ("ring-buffer: Set new size of the ring buffer sub page") Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.