From patchwork Fri Nov 1 17:35:15 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 11223541 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 42D421747 for ; Fri, 1 Nov 2019 17:35:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 239B121855 for ; Fri, 1 Nov 2019 17:35:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Dm1aJdKj" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729812AbfKARfZ (ORCPT ); Fri, 1 Nov 2019 13:35:25 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:52181 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727988AbfKARfZ (ORCPT ); Fri, 1 Nov 2019 13:35:25 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1572629724; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=bQVPVip8ff0LcfPaTnPD2rpsZ9HBejI/JIzJ0jq//Ps=; b=Dm1aJdKjRmY8+wc4naer/Kd0Acg5LKpbt+yDsjsZdYkMNYo+j+zAMr2DaiDXbT4TRZU038 zuMBX03CNnm3uv0wxV1MYdC9rERpW3cUsoYmE6OZH+RVVaGYxwQSOcvaEB8ZJvRvUrV2tQ 8qivf5Cvx9KgdnljbkXvNTThq1PfSY8= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-287-pqc9grtDOSGwWyyMavPlOA-1; Fri, 01 Nov 2019 13:35:21 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 35FA82EDC; Fri, 1 Nov 2019 17:35:19 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-121-40.rdu2.redhat.com [10.10.121.40]) by smtp.corp.redhat.com (Postfix) with ESMTP id 965F619C58; Fri, 1 Nov 2019 17:35:16 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 Subject: [RFC PATCH 08/11] pipe: Rearrange sequence in pipe_write() to preallocate slot [ver #3] From: David Howells To: torvalds@linux-foundation.org Cc: dhowells@redhat.com, Rasmus Villemoes , Greg Kroah-Hartman , Peter Zijlstra , nicolas.dichtel@6wind.com, raven@themaw.net, Christian Brauner , dhowells@redhat.com, keyrings@vger.kernel.org, linux-usb@vger.kernel.org, linux-block@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 01 Nov 2019 17:35:15 +0000 Message-ID: <157262971590.13142.1426435250123334464.stgit@warthog.procyon.org.uk> In-Reply-To: <157262963995.13142.5568934007158044624.stgit@warthog.procyon.org.uk> References: <157262963995.13142.5568934007158044624.stgit@warthog.procyon.org.uk> User-Agent: StGit/unknown-version MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-MC-Unique: pqc9grtDOSGwWyyMavPlOA-1 X-Mimecast-Spam-Score: 0 Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org Rearrange the sequence in pipe_write() so that the allocation of the new buffer, the allocation of a ring slot and the attachment to the ring is done under the pipe wait spinlock and then the lock is dropped and the buffer can be filled. The data copy needs to be done with the spinlock unheld and irqs enabled, so the lock needs to be dropped first. However, the reader can't progress as we're holding pipe->mutex. We also need to drop the lock as that would impact others looking at the pipe waitqueue, such as poll(), the consumer and a future kernel message writer. We just abandon the preallocated slot if we get a copy error. Future writes may continue it and a future read will eventually recycle it. Signed-off-by: David Howells --- fs/pipe.c | 51 +++++++++++++++++++++++++++++++++------------------ 1 file changed, 33 insertions(+), 18 deletions(-) diff --git a/fs/pipe.c b/fs/pipe.c index c16950e36ded..ce77ac0d8901 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -387,7 +387,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from) { struct file *filp = iocb->ki_filp; struct pipe_inode_info *pipe = filp->private_data; - unsigned int head, tail, max_usage, mask; + unsigned int head, max_usage, mask; ssize_t ret = 0; int do_wakeup = 0; size_t total_len = iov_iter_count(from); @@ -405,14 +405,13 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from) goto out; } - tail = pipe->tail; head = pipe->head; max_usage = pipe->max_usage; mask = pipe->ring_size - 1; /* We try to merge small writes */ chars = total_len & (PAGE_SIZE-1); /* size of the last buffer */ - if (!pipe_empty(head, tail) && chars != 0) { + if (!pipe_empty(head, pipe->tail) && chars != 0) { struct pipe_buffer *buf = &pipe->bufs[(head - 1) & mask]; int offset = buf->offset + buf->len; @@ -441,8 +440,8 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from) break; } - tail = pipe->tail; - if (!pipe_full(head, tail, max_usage)) { + head = pipe->head; + if (!pipe_full(head, pipe->tail, max_usage)) { struct pipe_buffer *buf = &pipe->bufs[head & mask]; struct page *page = pipe->tmp_page; int copied; @@ -455,40 +454,56 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from) } pipe->tmp_page = page; } + + /* Allocate a slot in the ring in advance and attach an + * empty buffer. If we fault or otherwise fail to use + * it, either the reader will consume it or it'll still + * be there for the next write. + */ + spin_lock_irq(&pipe->wait.lock); + + head = pipe->head; + pipe->head = head + 1; + /* Always wake up, even if the copy fails. Otherwise * we lock up (O_NONBLOCK-)readers that sleep due to * syscall merging. * FIXME! Is this really true? */ - do_wakeup = 1; - copied = copy_page_from_iter(page, 0, PAGE_SIZE, from); - if (unlikely(copied < PAGE_SIZE && iov_iter_count(from))) { - if (!ret) - ret = -EFAULT; - break; - } - ret += copied; + wake_up_interruptible_sync_poll_locked( + &pipe->wait, EPOLLIN | EPOLLRDNORM); + + spin_unlock_irq(&pipe->wait.lock); + kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN); /* Insert it into the buffer array */ + buf = &pipe->bufs[head & mask]; buf->page = page; buf->ops = &anon_pipe_buf_ops; buf->offset = 0; - buf->len = copied; + buf->len = 0; buf->flags = 0; if (is_packetized(filp)) { buf->ops = &packet_pipe_buf_ops; buf->flags = PIPE_BUF_FLAG_PACKET; } - - head++; - pipe->head = head; pipe->tmp_page = NULL; + copied = copy_page_from_iter(page, 0, PAGE_SIZE, from); + if (unlikely(copied < PAGE_SIZE && iov_iter_count(from))) { + if (!ret) + ret = -EFAULT; + break; + } + ret += copied; + buf->offset = 0; + buf->len = copied; + if (!iov_iter_count(from)) break; } - if (!pipe_full(head, tail, max_usage)) + if (!pipe_full(head, pipe->tail, max_usage)) continue; /* Wait for buffer space to become available. */