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 X-Spam-Level: X-Spam-Status: No, score=-14.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9A64DC43381 for ; Wed, 27 Mar 2019 19:09:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6F1312064A for ; Wed, 27 Mar 2019 19:09:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553713762; bh=MKmegbwWFokvZV2NvnOItwc+dad/+Fh7aYq23YYMn2E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Hhvk3uzfNJ8m/bfncvs1vR587manv0XZIGZFQG+rwNowjeSuhUwAfM96qkgQZhLNm 2N6KZKrE7Y1iDUsBQyZ86xEdVThIzbXxAn8TAqwraE1Wg8wN/fOMUGWFi0slPlajdT RovQ7t2HwbGQWVM8ipd7xNrSGAO4tBKiJd7Uupkg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389432AbfC0TJQ (ORCPT ); Wed, 27 Mar 2019 15:09:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:53962 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388744AbfC0SLg (ORCPT ); Wed, 27 Mar 2019 14:11:36 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 83EAE21741; Wed, 27 Mar 2019 18:11:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553710295; bh=MKmegbwWFokvZV2NvnOItwc+dad/+Fh7aYq23YYMn2E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=2gUqk5lMxl3B6ThNZwjYusLRvZoUlGfYyLbG01ZfVXVnyJXtP20tX1weRDDMt+Fsi ux/eibgreuKAXMRsNoHY+PnSdx5R4ptJw2bryiOdBOHOYP9TjQ+6aZ+OI6OvURq0eS LpmZq30Xuayiul/TDEVb0+ca6IM7JrqmQzd8wb2w= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Slavomir Kaslev , Linus Torvalds , Sasha Levin , linux-fsdevel@vger.kernel.org Subject: [PATCH AUTOSEL 4.19 040/192] fs: Make splice() and tee() take into account O_NONBLOCK flag on pipes Date: Wed, 27 Mar 2019 14:07:52 -0400 Message-Id: <20190327181025.13507-40-sashal@kernel.org> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20190327181025.13507-1-sashal@kernel.org> References: <20190327181025.13507-1-sashal@kernel.org> MIME-Version: 1.0 X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Slavomir Kaslev [ Upstream commit ee5e001196d1345b8fee25925ff5f1d67936081e ] The current implementation of splice() and tee() ignores O_NONBLOCK set on pipe file descriptors and checks only the SPLICE_F_NONBLOCK flag for blocking on pipe arguments. This is inconsistent since splice()-ing from/to non-pipe file descriptors does take O_NONBLOCK into consideration. Fix this by promoting O_NONBLOCK, when set on a pipe, to SPLICE_F_NONBLOCK. Some context for how the current implementation of splice() leads to inconsistent behavior. In the ongoing work[1] to add VM tracing capability to trace-cmd we stream tracing data over named FIFOs or vsockets from guests back to the host. When we receive SIGINT from user to stop tracing, we set O_NONBLOCK on the input file descriptor and set SPLICE_F_NONBLOCK for the next call to splice(). If splice() was blocked waiting on data from the input FIFO, after SIGINT splice() restarts with the same arguments (no SPLICE_F_NONBLOCK) and blocks again instead of returning -EAGAIN when no data is available. This differs from the splice() behavior when reading from a vsocket or when we're doing a traditional read()/write() loop (trace-cmd's --nosplice argument). With this patch applied we get the same behavior in all situations after setting O_NONBLOCK which also matches the behavior of doing a read()/write() loop instead of splice(). This change does have potential of breaking users who don't expect EAGAIN from splice() when SPLICE_F_NONBLOCK is not set. OTOH programs that set O_NONBLOCK and don't anticipate EAGAIN are arguably buggy[2]. [1] https://github.com/skaslev/trace-cmd/tree/vsock [2] https://github.com/torvalds/linux/blob/d47e3da1759230e394096fd742aad423c291ba48/fs/read_write.c#L1425 Signed-off-by: Slavomir Kaslev Reviewed-by: Steven Rostedt (VMware) Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- fs/splice.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/fs/splice.c b/fs/splice.c index 29e92b506394..7769181aa1a6 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -1119,6 +1119,9 @@ static long do_splice(struct file *in, loff_t __user *off_in, if (ipipe == opipe) return -EINVAL; + if ((in->f_flags | out->f_flags) & O_NONBLOCK) + flags |= SPLICE_F_NONBLOCK; + return splice_pipe_to_pipe(ipipe, opipe, len, flags); } @@ -1144,6 +1147,9 @@ static long do_splice(struct file *in, loff_t __user *off_in, if (unlikely(ret < 0)) return ret; + if (in->f_flags & O_NONBLOCK) + flags |= SPLICE_F_NONBLOCK; + file_start_write(out); ret = do_splice_from(ipipe, out, &offset, len, flags); file_end_write(out); @@ -1168,6 +1174,9 @@ static long do_splice(struct file *in, loff_t __user *off_in, offset = in->f_pos; } + if (out->f_flags & O_NONBLOCK) + flags |= SPLICE_F_NONBLOCK; + pipe_lock(opipe); ret = wait_for_space(opipe, flags); if (!ret) @@ -1717,6 +1726,9 @@ static long do_tee(struct file *in, struct file *out, size_t len, * copying the data. */ if (ipipe && opipe && ipipe != opipe) { + if ((in->f_flags | out->f_flags) & O_NONBLOCK) + flags |= SPLICE_F_NONBLOCK; + /* * Keep going, unless we encounter an error. The ipipe/opipe * ordering doesn't really matter. -- 2.19.1