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[104.155.91.135]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-482c9c0acaesm10806759f8f.29.2026.08.25.01.34.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Aug 2026 01:34:24 -0700 (PDT) Date: Tue, 25 Aug 2026 09:34:21 +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 1/2] tracing: Fix retry exhaustion in simple ring buffer reader swap Message-ID: References: <20260825-kernel-patch-1-v1-0-e9349aa0b165@gmail.com> <20260825-kernel-patch-1-v1-1-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-v1-1-e9349aa0b165@gmail.com> On Tue, Aug 25, 2026 at 01:20:37AM -0400, Ivan Immanuel Shaji via B4 Relay wrote: > From: Ivan Immanuel Shaji > > 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: stable@vger.kernel.org > Assisted-by: LLM sparse > Signed-off-by: Ivan Immanuel Shaji Reviewed-by: Vincent Donnefort > --- > 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 > >