From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 C96DC522F1A; Thu, 15 Oct 2026 13:34:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792071246; cv=none; b=bQ7e10uaLCQAX+P/yekOI/0fxOdOYyLgCtfwJ2dI9lPSga3HMiGV364U63Vvm2KNtLDCttgu7xqUa+D2X3LouC5YOju/30PWbgcoVTZO0DZxpFm5EbHQK/BtDG0RY9AVkkrHKTISp42YF2vNIRgkMpEDG58Vtop3BpvU5VS8AlA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792071246; c=relaxed/simple; bh=bPLL8TPErcbM5Bj5i4pKw+WqSiS9eCP4lZKMQrveDMI=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=KXAwBB4Qel11rc7G2B5NE8lsyioacENxyzYVGuCA2LvdE3Em9Z8LIifxQXuJaKzZo5miuFUalbAe/86IiDmnJVIr8WmlkjthPKA+l1rrjK60w78LJY7zBy9G1VK9XgHCd2cQa3xLKJgMKvDH8XWl6EPeFgKZYpQQcLNfRfv73yM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WuQi7FH4; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="WuQi7FH4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9F04B1F000C5; Thu, 15 Oct 2026 13:34:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792071244; bh=r7BXtOpv2uyoOOi5rjC+5uSD/dS7kT4PcmP95BYIThQ=; h=Date:From:To:Cc:Subject:References; b=WuQi7FH4fAxqLAdDYCiXPb9+zas3QUCIxbnMQEQNrdpNGGp5x9IvA5/56KUp8th7G Uy3mGTpyEPK+2lYpALy/0Boo85YvFxV5kvv5SUXbM5QlQMMYpBm3z0mCxPLeIlI5ky pVpddHJ1CClQUkmZ2OH9flE+MBPQzUYBiIEw1KakWz2+vVkjBFn1A1KtFnROPE+eAi FemU/xvnzWmSkRmUDFjxqZcIKGLr9KYDA2k9qb71U0T2ZDNZUJLrHEZ4M1mmowRebU CF+5bs8tOFQPeZ8ccYysd5rNElR93F9bkB8oj7KdLf5p8wiDDlE1C7PHEuqxSOQvew Uy6SNgdvs3i4A== Received: from rostedt by gandalf with local (Exim 4.100.1) (envelope-from ) id 1xHLat-00000000MeQ-40qP; Thu, 15 Oct 2026 09:34:03 -0400 Message-ID: <20261015133403.783087207@kernel.org> User-Agent: quilt/0.69 Date: Thu, 15 Oct 2026 09:33:19 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , stable@vger.kernel.org, syzbot+de3d7f9bcc9212f3fae1@syzkaller.appspotmail.com, Krystian Kaniewski , Vincent Donnefort Subject: [for-linus][PATCH 09/16] ring-buffer: Fix false warning in ring_buffer_map_get_reader() References: <20261015133310.731003448@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 From: Krystian Kaniewski The mmap reader can warn when it catches up with a writer that is still committing events. rb_get_reader_page() returns NULL in this case, but ring_buffer_map_get_reader() treats that result as an error. The initial rb_per_cpu_empty() check filters out an empty buffer, but it does not guarantee that the next reader page has committed data. Writers do not take reader_lock and can advance commit_page before publishing the committed length on the new page. rb_get_reader_page() can swap to that page, catch up with the writer and return NULL. Handle NULL through the existing no-data exit without warning. Remove the caller's reader_page == commit_page check as well, since the reader-page helper already handles that case. The existing metadata update and return path remain in place. Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260924084946.20104-1-krystianmkaniewski@gmail.com Fixes: 117c39200d9d ("ring-buffer: Introducing ring-buffer mapping functions") Assisted-by: Gemini:gemini-3.8-flash syzbot Reported-by: syzbot+de3d7f9bcc9212f3fae1@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=de3d7f9bcc9212f3fae1 Link: https://syzkaller.appspot.com/ai_job?id=488adc18-a10e-42d2-a205-25327c38837f Signed-off-by: Krystian Kaniewski Reviewed-by: Vincent Donnefort Signed-off-by: Steven Rostedt --- kernel/trace/ring_buffer.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index ad3bc48e2670..e2b721d0707f 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -7998,12 +7998,8 @@ int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu) goto out; } - /* Did the reader catch up with the writer? */ - if (cpu_buffer->reader_page == cpu_buffer->commit_page) - goto out; - reader = rb_get_reader_page(cpu_buffer); - if (WARN_ON(!reader)) + if (!reader) goto out; /* Check if any events were dropped */ -- 2.53.0