From patchwork Fri Jun 2 15:07:46 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 13265493 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 860C9C77B7A for ; Fri, 2 Jun 2023 15:09:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236466AbjFBPJa (ORCPT ); Fri, 2 Jun 2023 11:09:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57954 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236468AbjFBPJS (ORCPT ); Fri, 2 Jun 2023 11:09:18 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 443961BB for ; Fri, 2 Jun 2023 08:08:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1685718507; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=jyBtAHnxIDOUxFx8QcCqc48iyvS91zdxptS6bgS5LhE=; b=IRaCQqKzp3BsP8MtVhEkDqvXEAyWelhPTtq4FrlCcm2pwMbcq9F0ul2E6Na2owER2tnKV0 SsSNEZraE0aO9IJCrTV9wHQsmMB1Wu0xS+Y3nj2onOTPjDXRORHhNnre7IkFntVGAvOuHQ pBfUfqKTSbOuIrTp7lDbGVYviLVwRAo= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-652-HJKW5r7wNUG_h4BsM00Cfg-1; Fri, 02 Jun 2023 11:08:26 -0400 X-MC-Unique: HJKW5r7wNUG_h4BsM00Cfg-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 42DA4811E8F; Fri, 2 Jun 2023 15:08:25 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.42.28.182]) by smtp.corp.redhat.com (Postfix) with ESMTP id 30388492B00; Fri, 2 Jun 2023 15:08:22 +0000 (UTC) From: David Howells To: netdev@vger.kernel.org, Linus Torvalds Cc: David Howells , Chuck Lever , Boris Pismenny , John Fastabend , Jakub Kicinski , "David S. Miller" , Eric Dumazet , Paolo Abeni , Willem de Bruijn , David Ahern , Matthew Wilcox , Jens Axboe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Christoph Hellwig , Al Viro , Jan Kara , Jeff Layton , David Hildenbrand , Christian Brauner , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org Subject: [PATCH net-next v3 05/11] splice, net: Fix SPLICE_F_MORE signalling in splice_direct_to_actor() Date: Fri, 2 Jun 2023 16:07:46 +0100 Message-ID: <20230602150752.1306532-6-dhowells@redhat.com> In-Reply-To: <20230602150752.1306532-1-dhowells@redhat.com> References: <20230602150752.1306532-1-dhowells@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org splice_direct_to_actor() doesn't manage SPLICE_F_MORE correctly[1] - and, as a result, it incorrectly signals/fails to signal MSG_MORE when splicing to a socket. The problem I'm seeing happens when a short splice occurs because we got a short read due to hitting the EOF on a file: as the length read (read_len) is less than the remaining size to be spliced (len), SPLICE_F_MORE (and thus MSG_MORE) is set. The issue is that, for the moment, we have no way to know *why* the short read occurred and so can't make a good decision on whether we *should* keep MSG_MORE set. Further, the argument can be made that it should be left to userspace to decide how to handle it - userspace could perform some sort of cancellation for example. MSG_SENDPAGE_NOTLAST was added to work around this, but that is also set incorrectly under some circumstances - for example if a short read fills a single pipe_buffer, but the next read would return more (seqfile can do this). This was observed with the multi_chunk_sendfile tests in the tls kselftest program. Some of those tests would hang and time out when the last chunk of file was less than the sendfile request size: build/kselftest/net/tls -r tls.12_aes_gcm.multi_chunk_sendfile This has been observed before[2] and worked around in AF_TLS[3]. Fix this by making splice_direct_to_actor() always signal SPLICE_F_MORE if we haven't yet hit the requested operation size. SPLICE_F_MORE remains signalled if the user passed it in to splice() but otherwise gets cleared when we've read sufficient data to fulfill the request. The cleanup of a short splice to userspace is left to userspace. [!] Note that this changes user-visible behaviour. It will cause the multi_chunk_sendfile tests in the TLS kselftest to fail. This failure in the testsuite will be addressed in a subsequent patch by making userspace do a zero-length send(). It appears that SPLICE_F_MORE is only used by splice-to-socket. Signed-off-by: David Howells cc: Linus Torvalds cc: Jakub Kicinski cc: Jens Axboe cc: Christoph Hellwig cc: Al Viro cc: Matthew Wilcox cc: Jan Kara cc: Jeff Layton cc: David Hildenbrand cc: Christian Brauner cc: Chuck Lever cc: Boris Pismenny cc: John Fastabend cc: Eric Dumazet cc: "David S. Miller" cc: Paolo Abeni cc: linux-fsdevel@vger.kernel.org cc: linux-block@vger.kernel.org cc: linux-mm@kvack.org cc: netdev@vger.kernel.org Link: https://lore.kernel.org/r/499791.1685485603@warthog.procyon.org.uk/ [1] Link: https://lore.kernel.org/r/1591392508-14592-1-git-send-email-pooja.trivedi@stackpath.com/ [2] Link: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=d452d48b9f8b1a7f8152d33ef52cfd7fe1735b0a [3] --- fs/splice.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/fs/splice.c b/fs/splice.c index 9b1d43c0c562..c71bd8e03469 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -1052,13 +1052,17 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd, */ bytes = 0; len = sd->total_len; + + /* Don't block on output, we have to drain the direct pipe. */ flags = sd->flags; + sd->flags &= ~SPLICE_F_NONBLOCK; /* - * Don't block on output, we have to drain the direct pipe. + * We signal MORE until we've read sufficient data to fulfill the + * request and we keep signalling it if the caller set it. */ - sd->flags &= ~SPLICE_F_NONBLOCK; more = sd->flags & SPLICE_F_MORE; + sd->flags |= SPLICE_F_MORE; WARN_ON_ONCE(!pipe_empty(pipe->head, pipe->tail)); @@ -1074,14 +1078,12 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd, sd->total_len = read_len; /* - * If more data is pending, set SPLICE_F_MORE - * If this is the last data and SPLICE_F_MORE was not set - * initially, clears it. + * If we now have sufficient data to fulfill the request then + * we clear SPLICE_F_MORE if it was not set initially. */ - if (read_len < len) - sd->flags |= SPLICE_F_MORE; - else if (!more) + if (read_len >= len && !more) sd->flags &= ~SPLICE_F_MORE; + /* * NOTE: nonblocking mode only applies to the input. We * must not do the output in nonblocking mode as then we