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 0D2719475; Tue, 11 Jun 2024 22:53:06 +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=1718146386; cv=none; b=QwZn8khqsm7/WtnZEyCzp64hdKk0UxgyVGMZMRd+2lYli/4YmJ32nWxrICswyHpKmgqRCs5/DnA6GATO4M2xStMrha932xhUbuvcwSc2Eq8Z+7oG3BoE+l3LgOnnEzSZlf7WHIlxRpHkswfuh89odf0vLk3PU3adg8OKlDxamMw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718146386; c=relaxed/simple; bh=fhgz9IAmeJpMQtd4lfMk0iOiZf+Dwg8y0PO7LZ0iNAM=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=E/OeDK2x7dX90S19+OB6Jlc6JnLavNZ21CXYPGZHbeIJsJyvTNKvxQGoIWp3J4oVzkdQgFAzpqaElkq5anWF912Z6drxH6kxWK2K+k7qrStBT4g9SFh7jvKGrcJyUCNpCospTs4ISRUl06906yRlCFHqS2CjqepaMP/y8J/bFXE= 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 200E2C2BD10; Tue, 11 Jun 2024 22:53:03 +0000 (UTC) Date: Tue, 11 Jun 2024 18:53:19 -0400 From: Steven Rostedt To: Guenter Roeck Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort , Joel Fernandes , Daniel Bristot de Oliveira , Ingo Molnar , Peter Zijlstra , suleiman@google.com, Thomas Gleixner , Vineeth Pillai , Youssef Esmat , Beau Belgrave , Alexander Graf , Baoquan He , Borislav Petkov , "Paul E. McKenney" , David Howells , Mike Rapoport , Dave Hansen , Tony Luck , Ross Zwisler , Kees Cook Subject: Re: [PATCH v4 01/13] ring-buffer: Allow mapped field to be set without mapping Message-ID: <20240611185319.58a52a1b@gandalf.local.home> In-Reply-To: <5178e22b-0c00-48d2-8a6e-85510706f145@roeck-us.net> References: <20240611192828.691638177@goodmis.org> <20240611192907.402447387@goodmis.org> <5178e22b-0c00-48d2-8a6e-85510706f145@roeck-us.net> 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, 11 Jun 2024 15:43:59 -0700 Guenter Roeck wrote: > On 6/11/24 12:28, Steven Rostedt wrote: > > From: "Steven Rostedt (Google)" > > > > In preparation for having the ring buffer mapped to a dedicated location, > > which will have the same restrictions as user space memory mapped buffers, > > allow it to use the "mapped" field of the ring_buffer_per_cpu structure > > without having the user space meta page mapping. > > > > When this starts using the mapped field, it will need to handle adding a > > user space mapping (and removing it) from a ring buffer that is using a > > dedicated memory range. > > > > Signed-off-by: Steven Rostedt (Google) > > --- > > kernel/trace/ring_buffer.c | 11 ++++++++--- > > 1 file changed, 8 insertions(+), 3 deletions(-) > > > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > > index 28853966aa9a..78beaccf9c8c 100644 > > --- a/kernel/trace/ring_buffer.c > > +++ b/kernel/trace/ring_buffer.c > > @@ -5224,6 +5224,9 @@ static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer) > > { > > struct trace_buffer_meta *meta = cpu_buffer->meta_page; > > > > + if (!meta) > > + return; > > + > > meta->reader.read = cpu_buffer->reader_page->read; > > meta->reader.id = cpu_buffer->reader_page->id; > > meta->reader.lost_events = cpu_buffer->lost_events; > > @@ -6167,7 +6170,7 @@ rb_get_mapped_buffer(struct trace_buffer *buffer, int cpu) > > > > mutex_lock(&cpu_buffer->mapping_lock); > > > > - if (!cpu_buffer->mapped) { > > + if (!cpu_buffer->mapped || !cpu_buffer->meta_page) { > > mutex_unlock(&cpu_buffer->mapping_lock); > > return ERR_PTR(-ENODEV); > > } > > @@ -6359,12 +6362,13 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu, > > */ > > raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); > > rb_setup_ids_meta_page(cpu_buffer, subbuf_ids); > > + > > Picky again. Is that a leftover from something ? I don't see an immediate reason > for the added newline. Hmm, I could remove it. > > > raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); > > > > err = __rb_map_vma(cpu_buffer, vma); > > if (!err) { > > raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); > > - cpu_buffer->mapped = 1; > > + cpu_buffer->mapped++; > > raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); > > } else { > > kfree(cpu_buffer->subbuf_ids); > > @@ -6403,7 +6407,8 @@ int ring_buffer_unmap(struct trace_buffer *buffer, int cpu) > > mutex_lock(&buffer->mutex); > > raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); > > > > - cpu_buffer->mapped = 0; > > + WARN_ON_ONCE(!cpu_buffer->mapped); > > + cpu_buffer->mapped--; > > This will wrap to UINT_MAX if it was 0. Is that intentional ? If mapped is non zero, it limits what it can do. If it enters here as zero, we are really in a unknown state, so yeah, wrapping will just keep it limited. Which is a good thing. Do you want me to add a comment there? -- Steve > > > > > raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); > >