simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
post-decrements it only after a failed link replacement. On the final
attempt, a successful replacement leaves retry at zero, while a failed
replacement leaves it at -1.
The current !retry test reverses both outcomes. It returns an error after
a successful final replacement, leaving the link update complete but the
reader bookkeeping unfinished. After a failed final replacement, it
falls through and updates the head and reader pointers as though the
replacement succeeded, which can corrupt the ring.
Treat only a negative counter as exhaustion and return the documented
-EBUSY error.
Cc: [email protected]
Fixes: 34e5b958bd ("tracing: Introduce simple_ring_buffer")
Link: https://patch.msgid.link/[email protected]
Assisted-by: LLM sparse
Reviewed-by: Vincent Donnefort <[email protected]>
Signed-off-by: Ivan Immanuel Shaji <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]>
The unload_page callback expects the return value of load_page() as its
argument: ret = load_page(va); unload(ret). Fix the rollback code in
simple_ring_buffer_init_mm() where the descriptor's VA is used instead
of the loaded page address.
Link: https://patch.msgid.link/[email protected]
Fixes: 635923081c ("tracing: load/unload page callbacks for simple_ring_buffer")
Signed-off-by: Vincent Donnefort <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]>
nr_subbufs in the ring buffer metadata is always initialized to zero
because it is assigned from cpu_buffer->nr_pages before the page
initialization loop has run. While nr_subbufs is not currently read
by the kernel, it should reflect the actual buffer geometry in the
meta page for correctness.
Move the assignment after the page loop so that cpu_buffer->nr_pages
holds the final count.
Link: https://patch.msgid.link/[email protected]
Fixes: 34e5b958bd ("tracing: Introduce simple_ring_buffer")
Reviewed-by: Vincent Donnefort <[email protected]>
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: David Carlier <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]>
Add load/unload callback used for each admitted page in the ring-buffer.
This will be later useful for the pKVM hypervisor which uses a different
VA space and need to dynamically map/unmap the ring-buffer pages.
Link: https://patch.msgid.link/[email protected]
Reviewed-by: Steven Rostedt (Google) <[email protected]>
Signed-off-by: Vincent Donnefort <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>
Add a simple implementation of the kernel ring-buffer. This intends to
be used later by ring-buffer remotes such as the pKVM hypervisor, hence
the need for a cut down version (write only) without any dependency.
Link: https://patch.msgid.link/[email protected]
Reviewed-by: Steven Rostedt (Google) <[email protected]>
Signed-off-by: Vincent Donnefort <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>
Ivan Immanuel Shaji