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[104.155.91.135]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-482c9c146f1sm11512374f8f.33.2026.08.25.05.52.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Aug 2026 05:52:14 -0700 (PDT) Date: Tue, 25 Aug 2026 13:52:11 +0100 From: Vincent Donnefort To: Steven Rostedt Cc: sashiko-bot@kernel.org, sashiko-reviews@lists.linux.dev, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH v7 1/3] tracing: Fix subbuf resize races with trace_pipe_raw readers Message-ID: References: <20260817134750.3909384-1-vdonnefort@google.com> <20260817134750.3909384-2-vdonnefort@google.com> <20260817140812.2C7D41F00A3A@smtp.kernel.org> <20260822110424.346fa3c8@fedora> <20260824105315.27377f30@gandalf.local.home> <20260825084707.4c9cf9f5@gandalf.local.home> Precedence: bulk X-Mailing-List: linux-trace-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: <20260825084707.4c9cf9f5@gandalf.local.home> On Tue, Aug 25, 2026 at 08:47:07AM -0400, Steven Rostedt wrote: > On Tue, 25 Aug 2026 09:26:07 +0100 > Vincent Donnefort wrote: > > > > > Do you think it is still worth to reduce the window of discrepency between > > buffer->subbuf_order and buffer_page->order? > > Can you elaborate more on what you mean? > > -- Steve Something like this. @@ -7469,8 +7473,6 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) /* Make sure all commits have finished */ synchronize_rcu(); - buffer->subbuf_order = order; - /* Make sure all new buffers are allocated, before deleting the old ones */ for_each_buffer_cpu(buffer, cpu) { @@ -7500,6 +7502,7 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) /* Allocate the new size buffer */ INIT_LIST_HEAD(&cpu_buffer->new_pages); if (__rb_allocate_pages(cpu_buffer, nr_pages, + order, &cpu_buffer->new_pages)) { /* not enough memory for new pages */ err = -ENOMEM; @@ -7507,6 +7510,8 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) } } + buffer->subbuf_order = order; + for_each_buffer_cpu(buffer, cpu) { struct buffer_data_read_page old_free_data_page; struct list_head old_pages; But now with the idea of copying the data when data_page->order != reader_page->order, I am less convinced there's any gain. -- Vincent