From nobody Sat Feb 7 20:58:04 2026 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 0C053264A9D; Fri, 7 Nov 2025 13:07:56 +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=1762520877; cv=none; b=fu9DSZkUIV0DP0ZRESGWwSNryH8ihc5nPXdeyk6jwt2aOU46mUAsQ2jWkbbckQ43YF4Yq5gc5WYPyalI7G9TYW3RZrk2i67xA5C5jWIjkTO6FQe4MpUVuXNWA2yB5uLnwnai/DtzoSTYd4uFzbOXqndet6fgvJX9eFaDBnTlv2w= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762520877; c=relaxed/simple; bh=gTCe6+8DCvvTv/gwaosX0O1LJx32TQrppUBdFg7nEZ4=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=GNpGRsyTnQO02YHdK1M5W8CS24Bz3MaCvLXb44ZfGr5eskDEanp9L1KcISkGMP8sJiFcKK1DG+lLfbZDxPcUzCkYMmz/MGNMbNAOI2lMfe+RhzPTTC0MnM7YGgHPUqJ+o+y7ISq34/5qpA734qkY+H4pUj6vO6Sbn9KqcBYrWZg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GyHqf8Tw; 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="GyHqf8Tw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AB87EC19421; Fri, 7 Nov 2025 13:07:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762520876; bh=gTCe6+8DCvvTv/gwaosX0O1LJx32TQrppUBdFg7nEZ4=; h=Date:From:To:Cc:Subject:References:From; b=GyHqf8TwIU4rt1cFeUgO4fS4nNJ6DVg8ytscgRw4KL4L3gaewE1KKnGmw/TlKo/nM SI1mAPSUB/M1mDxvwmNJy+b+fFqF5cMQw4pnAvqNT/cR4+ejYkPpCvrinXK6/UrWYp FNyqKkviQLAASmtazERNk3yVPzwYzJuv+3VGFXKHoNafAFiph/IaSOohjasYUK/uds DvlYoDxN3oFoMwi+Jr7e9y2utGowRaqKFw0bDWMfr2uKxDhxUg/sEtIw4csAfP0QjZ 1xnfkBxLLiA7VzG2oq4TpEIpV8+Y0GRaSsL4BkBLXl0ide4d/CHQem41exgdfl0Pc9 OCIrQijE17auA== Received: from rostedt by gandalf with local (Exim 4.98.2) (envelope-from ) id 1vHMC6-00000000GGV-0MR2; Fri, 07 Nov 2025 08:07:58 -0500 Message-ID: <20251107130757.937218818@kernel.org> User-Agent: quilt/0.68 Date: Fri, 07 Nov 2025 08:07:31 -0500 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Tomas Glozar , John Kacur , stable@vger.kernel.org, Vincent Donnefort , syzbot+92a3745cea5ec6360309@syzkaller.appspotmail.com Subject: [for-linus][PATCH 1/3] ring-buffer: Do not warn in ring_buffer_map_get_reader() when reader catches up References: <20251107130730.158197641@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Steven Rostedt The function ring_buffer_map_get_reader() is a bit more strict than the other get reader functions, and except for certain situations the rb_get_reader_page() should not return NULL. If it does, it triggers a warning. This warning was triggering but after looking at why, it was because another acceptable situation was happening and it wasn't checked for. If the reader catches up to the writer and there's still data to be read on the reader page, then the rb_get_reader_page() will return NULL as there's no new page to get. In this situation, the reader page should not be updated and no warning should trigger. Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Cc: Vincent Donnefort Reported-by: syzbot+92a3745cea5ec6360309@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/690babec.050a0220.baf87.0064.GAE@google= .com/ Link: https://lore.kernel.org/20251016132848.1b11bb37@gandalf.local.home Fixes: 117c39200d9d7 ("ring-buffer: Introducing ring-buffer mapping functio= ns") Signed-off-by: Steven Rostedt (Google) --- kernel/trace/ring_buffer.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 1244d2c5c384..afcd3747264d 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -7344,6 +7344,10 @@ int ring_buffer_map_get_reader(struct trace_buffer *= buffer, int cpu) goto out; } =20 + /* Did the reader catch up with the writer? */ + if (cpu_buffer->reader_page =3D=3D cpu_buffer->commit_page) + goto out; + reader =3D rb_get_reader_page(cpu_buffer); if (WARN_ON(!reader)) goto out; --=20 2.51.0