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 E5D09A927; Tue, 27 May 2025 00:17:46 +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=1748305067; cv=none; b=h4kzAQOYXz4nBm17DhBZa1zydSGROm8w9dNWlgArhiqYXVD77qMMcmVIZisd8bSFEeDor0cHIQJfxvZjb04KhpKwi5UUQtqIS+nwC9OlKWh1TJ+GNouuGBKFwE+qF2t5zHnljbVoLgeU/kpTcNFGU6VIjIlgJ72lbWXk6nvyfww= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748305067; c=relaxed/simple; bh=wMr1HOcueB5Am6KF/Ss7kwFnpRQwGEkr9hpd5ICRctU=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=qHjVV7goBTRCDjUQ/JNaNgEJOkh6P6PO+MylprFteGNHgxcxajPBFHSZp07PBFgD/ssKwqrz/xnLHQ/r9ZAmCp9ntg19Ez6Otwk4HMoeyXL6Smq5UcXx2UG50rtfMfVoWEwyTuvz0/U0XViycnHLJcpa1tl182mwMKtiM1MResk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bJtR09PK; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bJtR09PK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 78129C4CEE7; Tue, 27 May 2025 00:17:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1748305066; bh=wMr1HOcueB5Am6KF/Ss7kwFnpRQwGEkr9hpd5ICRctU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=bJtR09PKSIGXNwtceQGOGnEOWVPbiYxFDrm6KgKis0CwtB6sQeCOjAENolVvYP3P2 +lnrLu6N0zBd4MxIrhS1ZbZSFWnDjqWFAY+5vGstfcOHjtjCOi6bgVz7AGfkEN/n6Q i/Q8zzuTiQNArcWc7Pqs7bEDhyJ4Y0s/GYtV7tdh60Fr9DBTAaeEu2+UOK6Z/JDxT+ HTK015xBK4ZluGjMFsRh6tG025HGC6p+rBn0nOs9EDbGYo27U8OeD3pjuLnF2gaeog tJt51ub3hCVwJjynlRw4+uGX6OGk1/0jRsUPs36GTHytRXJaQeUFfVBNG1gjvrjrq6 BK2tsBI/jK8gA== Date: Tue, 27 May 2025 09:17:43 +0900 From: Masami Hiramatsu (Google) To: Masami Hiramatsu (Google) Cc: Steven Rostedt , 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: <20250527091743.d036018195b7668aea0753c0@kernel.org> In-Reply-To: <20250526120342.cdcfca9ac3c2161d48c03af5@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> X-Mailer: Sylpheed 3.8.0beta1 (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 Mon, 26 May 2025 12:03:42 +0900 Masami Hiramatsu (Google) wrote: > On Fri, 23 May 2025 17:28:57 -0400 > Steven Rostedt wrote: > > > On Fri, 23 May 2025 16:54:25 -0400 > > Steven Rostedt wrote: > > > > > I think we also need this: > > > > > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > > > index 7d837963dd1e..456efebc396a 100644 > > > --- a/kernel/trace/ring_buffer.c > > > +++ b/kernel/trace/ring_buffer.c > > > @@ -3638,6 +3638,9 @@ rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer, > > > > > > rb_reset_tail(cpu_buffer, tail, info); > > > > > > + /* The new page should have zero committed */ > > > + rb_init_page(next_page->page); > > > + > > > /* Commit what we have for now. */ > > > rb_end_commit(cpu_buffer); > > > /* rb_end_commit() decs committing */ > > > > No we don't need it ;-) > > > > I'm looking deeper into the code and we have this: > > > > /* > > * No need to worry about races with clearing out the commit. > > * it only can increment when a commit takes place. But that > > * only happens in the outer most nested commit. > > */ > > local_set(&next_page->page->commit, 0); > > > > When the tail page gets moved. > > Yeah, when the page gets written, it is cleared. What about this? It seems if we keep the reader->page->commit, when we catch up the tail page, rb_get_reader_page() returns new reader (== tail) because reader->read(==0) < reader->page->commit. But we should not return new reader. diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 5034bae02f08..179142db9586 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5522,6 +5522,12 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) cpu_buffer->last_overrun = overwrite; } + /* But if we catch up to the tail, do not return reader page. */ + if (cpu_buffer->commit_page == cpu_buffer->reader_page) { + reader = NULL; + goto out; + } + goto again; out: -- Masami Hiramatsu (Google)