[PATCH v8 0/3] ring-buffer: Fixes for subbuf resizing and persistent buffers

[Vincent Donnefort <vdonnefort@google.com>]

This series addresses multiple issues discovered with the dynamic ring
buffer resizing.

I have managed to reproduce a ring_buffer_read_page() race with

 $ while true; do for i in 8 16 32; do echo $i > /sys/kernel/tracing/buffer_subbuf_size_kb; sleep 0.1; done; done

Changelog:

v8:

  - ring_buffer_read_page() handles gracefully read_page/reader_page
    order mismatch (Steven)

v7 (https://lore.kernel.org/linux-trace-kernel/20260817101533.1558223-1-vdonnefort@google.com/):

  - Match the "static" rb limit with bpage::id bitwidth
  - Cover another 32-bit truncation in rb_range_buffer (Sashiko)
  - Fix uninitialized spare_size (Sashiko)

v6 (https://lore.kernel.org/all/20260814154823.755406-1-vdonnefort@google.com/):

  - New prototype for ring_buffer_alloc_read_page() (Steven)
  - ring_buffer_read_page() to return -EAGAIN (Steven)
  - Keep nr_pages "unsigned long" (Steven)
  - Repase on ring-buffer/next (Drop most of the patches)

v5 (https://lore.kernel.org/all/20260813131152.3589632-1-vdonnefort@google.com/):

  - Reset info->spare_read only when data is in the ring-buffer (Sashiko)
  - Use `unsigned long` for subbuf_size declaration to avoid 32-bit
    truncation. (Sashiko)
  - Make cpu_buffer::free_page a buffer_read_data_page
  - Update kerneldoc for ring_buffer_alloc_read_page()

v4 (https://lore.kernel.org/all/20260812153311.2328812-1-vdonnefort@google.com/):

  - Add rb_subbuf_start() helper (Steven)
  - kerneldoc additions
  - Fix races in trace_pipe_raw readers
  - Use rb_subbuf_capacity() in ring_buffer_subbuf_order_set()
  - use rb_page_capacity() in ring_buffer_map_get_reader (Sashiko)
  - Fix 32-bit overflow in ring_buffer_subbuf_order_set() (Sashiko)
  - Hold cpu_buffer::lock when modifying cpu_buffer->free_page in
    ring_buffer_subbuf_order_set (Sashiko)

v3 (https://lore.kernel.org/all/20260810125633.3344684-1-vdonnefort@google.com/):

  - Drop first 3 patches (Rebased on 7.2-rc7)
  - Add a patch to align "nr_pages" to unsigned int
  - Add a patch to remove useless trace_buffer::cpus
  - Add unsigned long cast for rb_subbuf_size()
  - subbuf_order fix for rb_free_cpu_buffer() (Sashiko)
  - Use __always_inline just like the other accessors for the hot-path.

v2 (https://lore.kernel.org/all/20260806211306.3704194-1-vdonnefort@google.com/):

  - Prevent resizing of the persistent ring buffer
  - Add missing bpage::order init
  - Rework subbuf_size/subbuf_order (Sashiko)
  - Remove ring_buffer_per_cpu::mapped
  - Dynamically calculate trace_buffer::max_data_size

v1 (https://lore.kernel.org/all/20260805153225.2096152-1-vdonnefort@google.com/)

Vincent Donnefort (3):
  tracing: Fix subbuf resize races with trace_pipe_raw readers
  ring-buffer: Cap static ring buffer nr_pages
  ring-buffer: Prevent truncation of nr_pages / nr_subbufs

 include/linux/ring_buffer.h          |   5 +-
 kernel/trace/ring_buffer.c           | 198 ++++++++++++++++++---------
 kernel/trace/ring_buffer_benchmark.c |   6 +-
 kernel/trace/trace.c                 |  94 ++++++-------
 kernel/trace/trace.h                 |   9 +-
 5 files changed, 185 insertions(+), 127 deletions(-)


base-commit: 66498c75b4f8017f62d720d9b59675bdf3abce91
-- 
2.55.0.860.g4b6b3295ed-goog