From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E08FEC001B0 for ; Fri, 11 Aug 2023 11:43:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229700AbjHKLnE (ORCPT ); Fri, 11 Aug 2023 07:43:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47210 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229592AbjHKLnD (ORCPT ); Fri, 11 Aug 2023 07:43:03 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EF342FA; Fri, 11 Aug 2023 04:43:02 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 8979465644; Fri, 11 Aug 2023 11:43:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A5C46C433C8; Fri, 11 Aug 2023 11:43:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1691754182; bh=TQCzZnkuHpoP3dZH4vAu/XWOXP2gTQQ50jakD2TlpKw=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=IgZXuvBY5QTt7Q4pQ8U7wQrHHy58ToautzIhnNzAXAuVeDALFOjGgIU5dJcd35QCO awT88MoBf4W0F5QUUBJfGMh8e3eepiEB6BrYo/hIBCh0pGHzwN3jKtZuKe+WH2X41f jIS9zSZbCB7v+L0CKeF/VYQkqaJpO6w4SMsItpzElLkPOs9P83iAPPXu21qIMj4d8O bLhKPo1V5/5uzP9Mj8ttG2M3rHcgl5OKHKDX8B/Drs70YHaUatKufAKZPogxdVm+Ws uFt+EQeRU6uqOANckN79NjGUxCSLYUIrFoM7WzFkDg/fXWY4THEkl6J8YWmjPTmsnF ss1zD78PnZg6g== Date: Fri, 11 Aug 2023 20:42:57 +0900 From: Masami Hiramatsu (Google) To: Zheng Yejian Cc: , , , Subject: Re: [PATCH] tracing: Fix race when concurrently splice_read trace_pipe Message-Id: <20230811204257.99df8ba60d591f5bace38615@kernel.org> In-Reply-To: <20230810123905.1531061-1-zhengyejian1@huawei.com> References: <20230810123905.1531061-1-zhengyejian1@huawei.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org On Thu, 10 Aug 2023 20:39:05 +0800 Zheng Yejian wrote: > When concurrently splice_read file trace_pipe and per_cpu/cpu*/trace_pipe, > there are more data being read out than expected. > > The root cause is that in tracing_splice_read_pipe(), an entry is found > outside locks, it may be read by multiple readers or consumed by other > reader as starting printing it. > > To fix it, change to find entry after holding locks. > > Fixes: 7e53bd42d14c ("tracing: Consolidate protection of reader access to the ring buffer") > Signed-off-by: Zheng Yejian > --- > kernel/trace/trace.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index b8870078ef58..f169d33b948f 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -7054,14 +7054,16 @@ static ssize_t tracing_splice_read_pipe(struct file *filp, > if (ret <= 0) > goto out_err; > > - if (!iter->ent && !trace_find_next_entry_inc(iter)) { > + trace_event_read_lock(); > + trace_access_lock(iter->cpu_file); > + > + if (!trace_find_next_entry_inc(iter)) { It seems you skips '!iter->ent' check. Is there any reason for this change? Thank you, > + trace_access_unlock(iter->cpu_file); > + trace_event_read_unlock(); > ret = -EFAULT; > goto out_err; > } > > - trace_event_read_lock(); > - trace_access_lock(iter->cpu_file); > - > /* Fill as many pages as possible. */ > for (i = 0, rem = len; i < spd.nr_pages_max && rem; i++) { > spd.pages[i] = alloc_page(GFP_KERNEL); > -- > 2.25.1 > -- Masami Hiramatsu (Google)