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[104.155.91.135]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-499d6364720sm22212585e9.12.2026.08.25.01.39.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Aug 2026 01:39:41 -0700 (PDT) Date: Tue, 25 Aug 2026 09:39:38 +0100 From: Vincent Donnefort To: ivanimmanuel1234@gmail.com Cc: Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 2/2] ring-buffer: Stop remote reader update when page swap fails Message-ID: References: <20260825-kernel-patch-1-v1-0-e9349aa0b165@gmail.com> <20260825-kernel-patch-1-v1-2-e9349aa0b165@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260825-kernel-patch-1-v1-2-e9349aa0b165@gmail.com> On Tue, Aug 25, 2026 at 01:20:38AM -0400, Ivan Immanuel Shaji via B4 Relay wrote: > From: Ivan Immanuel Shaji > > The remote swap_reader_page callback can fail when the writer moves the > head before the remote catches it. __rb_get_reader_page_from_remote() > warns about that failure but continues with the unchanged reader ID and > rearranges the local page list as though the swap succeeded. > > Stop immediately after warning. Callers already handle a NULL reader > page as a failed attempt, and this avoids splicing the same page as both > the previous and new reader. > > 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 | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 3c3ed639923d..d11b2759caac 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -5805,8 +5805,9 @@ __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 (WARN_ON_ONCE(cpu_buffer->remote->swap_reader_page(cpu_buffer->cpu, > + cpu_buffer->remote->priv))) > + 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 > > If handled gracefully and as this can be triggered by a storm of events on small buffer (when -EBUSY) I wonder if we shouldn't use a pr_warn_ratelimited() instead of a WARN()? -- Vincent