From: Ivan Immanuel Shaji Date: Tue, 25 Aug 2026 12:52:50 -0400 Subject: [PATCH v2 2/2] ring-buffer: Stop remote reader update when page swap fails MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260825-kernel-patch-1-v2-2-bb3461807a32@gmail.com> References: <20260825-kernel-patch-1-v2-0-bb3461807a32@gmail.com> In-Reply-To: <20260825-kernel-patch-1-v2-0-bb3461807a32@gmail.com> To: Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Vincent Donnefort Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, stable@vger.kernel.org, Ivan Immanuel Shaji X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1787676803; l=1736; i=ivanimmanuel1234@gmail.com; s=20260825; h=from:subject:message-id; bh=LNL2ffJz8llLBy4R+x3iJYnTiH9lI0OfoRC4hz5apiw=; b=QJKEN/5hZjtWkMBMH/i//qnraPVZXGGRR6NaiSx4oqq97BchClSXatijJio6RkkoNRwlXovwC VCPjsCR5Th5DCwPrek+JH9QfoB5TYU6QQAzsDO/Dc1D+/dccnIybkcB X-Developer-Key: i=ivanimmanuel1234@gmail.com; a=ed25519; pk=Wx8O3UUs3XneDkbqbOJJnlNdWSpEf2tWbTAoE7/vnqE= X-Endpoint-Received: by B4 Relay for ivanimmanuel1234@gmail.com/20260825 with auth_id=975 List-Id: B4 Relay Submissions The remote swap_reader_page callback can return -EBUSY when the writer moves the head before the remote catches it, particularly during an event storm on a small buffer. __rb_get_reader_page_from_remote() currently warns about that failure but continues with the unchanged reader ID and rearranges the local page list as though the swap succeeded. Handle the callback failure as a recoverable error. Report it with pr_warn_ratelimited() and return NULL. Callers already handle a NULL reader page as a failed attempt. This avoids splicing the same page as both the previous and new reader without flooding the log under contention. Fixes: 2e67fabd8b77 ("ring-buffer: Introduce ring-buffer remotes") Cc: stable@vger.kernel.org Assisted-by: LLM sparse Signed-off-by: Ivan Immanuel Shaji --- kernel/trace/ring_buffer.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 3c3ed639923d..b0963ac6fd16 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5805,8 +5805,11 @@ __rb_get_reader_page_from_remote(struct ring_buffer_per_cpu *cpu_buffer) prev_reader = cpu_buffer->subbuf_ids[cpu_buffer->meta_page->reader.id]; - WARN_ON_ONCE(cpu_buffer->remote->swap_reader_page(cpu_buffer->cpu, - cpu_buffer->remote->priv)); + if (cpu_buffer->remote->swap_reader_page(cpu_buffer->cpu, + cpu_buffer->remote->priv)) { + pr_warn_ratelimited("Remote reader page swap failed\n"); + return NULL; + } /* nr_pages doesn't include the reader page */ if (WARN_ON_ONCE(cpu_buffer->meta_page->reader.id > cpu_buffer->nr_pages)) return NULL; -- 2.53.0