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[104.155.91.135]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6a9d0ef7228sm3569166a12.9.2026.09.15.00.16.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Sep 2026 00:16:18 -0700 (PDT) Date: Tue, 15 Sep 2026 08:16:15 +0100 From: Vincent Donnefort To: David Carlier Cc: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] ring-buffer: Take cpus_read_lock() when changing the subbuf order Message-ID: References: <20260914182850.21449-1-devnexen@gmail.com> Precedence: bulk X-Mailing-List: stable@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: <20260914182850.21449-1-devnexen@gmail.com> On Mon, Sep 14, 2026 at 07:28:43PM +0100, David Carlier wrote: > A CPU coming online during ring_buffer_subbuf_order_set() can be added nit: a "new" CPU or "A CPU we've never seen before"? Offlined CPUs aren't removed from ->cpumask. > to buffer->cpumask after the allocation loop, and the install loop then > uses its empty new_pages list, corrupting the buffer. > > Take cpus_read_lock() as ring_buffer_resize() does. > > Fixes: f9b94daa542a ("ring-buffer: Set new size of the ring buffer sub page") > Cc: stable@vger.kernel.org > Signed-off-by: David Carlier > --- > kernel/trace/ring_buffer.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 04bb94c29f58..445931bc9ae0 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -7464,6 +7464,12 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) > if (psize > RB_WRITE_MASK + 1) > return -EINVAL; > > + /* > + * Keep CPUs from coming online while changing the order to > + * synchronize with new per CPU buffers being created. > + */ Can we drop this comment? cpus_read_lock is self-explanatory. > + guard(cpus_read_lock)(); > + > /* prevent another thread from changing buffer sizes */ > guard(mutex)(&buffer->mutex); > > -- > 2.55.0 > -- Vincent