On Tue, Aug 25, 2026 at 01:20:37AM -0400, Ivan Immanuel Shaji via B4 Relay wrote:
From: Ivan Immanuel Shaji <redacted>
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.
Fixes: 34e5b958bdad ("tracing: Introduce simple_ring_buffer")
Cc: <redacted>
Assisted-by: LLM sparse
Signed-off-by: Ivan Immanuel Shaji <redacted>
Reviewed-by: Vincent Donnefort <vdonnefort@google.com>
quoted hunk ↗ jump to hunk
---
kernel/trace/simple_ring_buffer.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/simple_ring_buffer.c b/kernel/trace/simple_ring_buffer.c
index f4642f5adda3..49913bb0057a 100644
--- a/kernel/trace/simple_ring_buffer.c
+++ b/kernel/trace/simple_ring_buffer.c
@@ -160,8 +160,8 @@ int simple_ring_buffer_swap_reader_page(struct simple_rb_per_cpu *cpu_buffer)
overrun = cpu_buffer->meta->overrun;
} while (!simple_bpage_unset_head_link(last, reader, SIMPLE_RB_LINK_NORMAL) && retry--);
- if (!retry)
- return -EINVAL;
+ if (retry < 0)
+ return -EBUSY;
cpu_buffer->head_page = simple_bpage_from_link(reader->link.next);
cpu_buffer->head_page->link.prev = &reader->link;
--
2.53.0