From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 93D761DFCE; Tue, 27 May 2025 13:47:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748353621; cv=none; b=HPiqX8Mvwdm4rA2i9jDSw5JRNe8FUejBd+b5E5Cddt3b/XISvAGJaVatMP0ZK1XoR6FZA4Rojzbwv5sUVfABmvzMgCbq0wD2ulaggArH7LBOhaJK7LFTcC7RMacIctKHQ20Jtx8AwysKD/bIw3W3a9e5s099aZNKRRh+9f9wIkQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748353621; c=relaxed/simple; bh=druQO90/3aoZGZpAmzbmlfxa785/GK+2GPpQUanFOok=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=mZNFAaqUk9HTq0apwZIwnRnbXwpZsU49bfG8frCggTN/qiVF6X0Ext8qY36Kv4P1fqxRCIjd98js0E5fIxMVsZT986dEYNvZ6BTN5zKvs51OW6wTTc3Ny+JHV3c4slRJY4atsHvMBsSXbHXRsr3hbo5CDdQWTvXh07G6iYSn2OA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7CCFCC4CEE9; Tue, 27 May 2025 13:47:00 +0000 (UTC) Date: Tue, 27 May 2025 09:47:57 -0400 From: Steven Rostedt To: "Masami Hiramatsu (Google)" Cc: Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH v3 1/2] tracing: ring_buffer: Rewind persistent ring buffer when reboot Message-ID: <20250527094757.791e8f10@gandalf.local.home> In-Reply-To: <20250527125444.80e59e659a7f087fed3c6fc9@kernel.org> References: <174792927500.496143.10668210464102033012.stgit@mhiramat.tok.corp.google.com> <174792928413.496143.17979267710069360561.stgit@mhiramat.tok.corp.google.com> <20250523165425.0275c9a1@gandalf.local.home> <20250523172857.02ab4a75@gandalf.local.home> <20250526120342.cdcfca9ac3c2161d48c03af5@kernel.org> <20250527091743.d036018195b7668aea0753c0@kernel.org> <20250527121549.2d40608e9463199d85bf9ba4@kernel.org> <20250527125444.80e59e659a7f087fed3c6fc9@kernel.org> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) 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-Transfer-Encoding: 7bit On Tue, 27 May 2025 12:54:44 +0900 Masami Hiramatsu (Google) wrote: > Here is what I meant. As far as I ran my test, it looks good (it prevents > over-read by `cat per_cpu/cpu0/trace_pipe_raw`) > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 5034bae02f08..de1831eb3446 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -5405,6 +5405,7 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) > unsigned long flags; > int nr_loops = 0; > bool ret; > + u64 ts; > > local_irq_save(flags); > arch_spin_lock(&cpu_buffer->lock); > @@ -5423,6 +5424,18 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) > > reader = cpu_buffer->reader_page; > > + /* > + * Now the page->commit is not cleared when it read. > + * Check whether timestamp is newer instead. We also don't > + * care the head_page is overwritten. In that case, timestamp > + * should be newer than reader timestamp too. > + */ > + ts = cpu_buffer->head_page->page->time_stamp; > + if (ts < reader->page->time_stamp) { Hmm, I think this test may be too fragile. The head_page can be moved by the writer, and this would need to handle races. I found an issue with commit overflow and have a couple of bugs to fix that touches some of this code. Let's revisit after I get those fixed. Thanks, -- Steve > + reader = NULL; > + goto out; > + } > + > /* If there's more to read, return this page */ > if (cpu_buffer->reader_page->read < rb_page_size(reader)) > goto out; >