From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-239000-1516218065-2-16874324304218981996 X-Sieve: CMU Sieve 3.0 X-Spam-known-sender: no X-Spam-score: 0.0 X-Spam-hits: BAYES_00 -1.9, HEADER_FROM_DIFFERENT_DOMAINS 0.25, RCVD_IN_DNSWL_HI -5, T_RP_MATCHES_RCVD -0.01, LANGUAGES en, BAYES_USED global, SA_VERSION 3.4.0 X-Spam-source: IP='209.132.180.67', Host='vger.kernel.org', Country='US', FromHeader='de', MailFrom='org' X-Spam-charsets: X-Resolved-to: greg@kroah.com X-Delivered-to: greg@kroah.com X-Mail-from: linux-api-owner@vger.kernel.org ARC-Seal: i=1; a=rsa-sha256; cv=none; d=messagingengine.com; s=arctest; t=1516218063; b=shJPcEOgG1+y5iQtZyRIXrnj1XwAd9fqQ4uDTcFmp8OGWm2 mMQ8NoU9aVtdaNxQNYzAX5zAXuxATSstvGAV09DUUNZ24/7ElRePUgFBr6OdhZEJ Kboa9gJM+7S47jtMkkPf2OAnitwtq6QCdCxGBfYkgqZcn1cZsy8LoAOQk1CKT+pa qPYVNlHHUWuPIncvSmdNiwlJJOzCz6CgZ/IoPUbi/EtVJTgk44Jj5ANQxGe4+SJw HVFR1PWxlrswbYPaWxabPMQVFURU6rVjoJ31DgyKNDP5LLGklb2T9kM8Tv3CVk8i UwU9qLZStcOnOXRW1MxEvqkgK0REIhLJP6wwMqw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=from:to:cc:subject:date:message-id :in-reply-to:references:sender:list-id; s=arctest; t=1516218063; bh=8tobXlXxyQZbJkdjl3yVb2Bh3VaOvmlK+hRnKh1paw0=; b=k8oitfs2f5o6 NDALoflxSIebI2vKYvgfom57CdgN6mSfJJJf5yb7PfIIxFUuwuxlmFs72uQoeVWD BLuQ2V1t0vrlglBj6p+I+jcydZu/jw7UegdBwL5wZLKnG5DYKeV9AUrwrgAaah0H VBO5p831FeIYGk4uJzkqiyA4hBtWTMuW28UVfH2FQ92ihiA2AGmKgwnAoAYGECL0 15R3qQQTLf71mAcSmPNXS2O5XdX2BurSj/VY5SOuWpT0nm6ddSUQUqC49I+V96/R Mc/9Kbidj/egafSA/bvlj2mfw+ixU81NanWZqQZdKpz3muhH91RWrJKtcL86ycBe h3Bcpglf/A== ARC-Authentication-Results: i=1; mx1.messagingengine.com; arc=none (no signatures found); dkim=fail (message has been altered; 2048-bit rsa key sha256) header.d=infradead.org header.i=@infradead.org header.b=N2XZvoGR x-bits=2048 x-keytype=rsa x-algorithm=sha256 x-selector=bombadil.20170209; dmarc=none (p=none,has-list-id=yes,d=none) header.from=lst.de; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=linux-api-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=lst.de header.result=pass header_is_org_domain=yes Authentication-Results: mx1.messagingengine.com; arc=none (no signatures found); dkim=fail (message has been altered; 2048-bit rsa key sha256) header.d=infradead.org header.i=@infradead.org header.b=N2XZvoGR x-bits=2048 x-keytype=rsa x-algorithm=sha256 x-selector=bombadil.20170209; dmarc=none (p=none,has-list-id=yes,d=none) header.from=lst.de; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=linux-api-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=lst.de header.result=pass header_is_org_domain=yes Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750816AbeAQT2G (ORCPT ); Wed, 17 Jan 2018 14:28:06 -0500 Received: from bombadil.infradead.org ([65.50.211.133]:50225 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753117AbeAQT2E (ORCPT ); Wed, 17 Jan 2018 14:28:04 -0500 From: Christoph Hellwig To: viro@zeniv.linux.org.uk Cc: Avi Kivity , linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, netdev@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 05/36] aio: simplify cancellation Date: Wed, 17 Jan 2018 20:27:11 +0100 Message-Id: <20180117192742.710-6-hch@lst.de> X-Mailer: git-send-email 2.14.2 In-Reply-To: <20180117192742.710-1-hch@lst.de> References: <20180117192742.710-1-hch@lst.de> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-api-owner@vger.kernel.org X-Mailing-List: linux-api@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: With the current aio code there is no need for the magic KIOCB_CANCELLED value, as a cancelation just kicks the driver to queue the completion ASAP, with all actual completion handling done in another thread. Given that both the completion path and cancelation take the context lock there is no need for magic cmpxchg loops either. Signed-off-by: Christoph Hellwig Acked-by: Jeff Moyer --- fs/aio.c | 37 +++++++++---------------------------- 1 file changed, 9 insertions(+), 28 deletions(-) diff --git a/fs/aio.c b/fs/aio.c index c32c315f05b5..2d40cf5dd4ec 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -156,19 +156,6 @@ struct kioctx { unsigned id; }; -/* - * We use ki_cancel == KIOCB_CANCELLED to indicate that a kiocb has been either - * cancelled or completed (this makes a certain amount of sense because - * successful cancellation - io_cancel() - does deliver the completion to - * userspace). - * - * And since most things don't implement kiocb cancellation and we'd really like - * kiocb completion to be lockless when possible, we use ki_cancel to - * synchronize cancellation and completion - we only set it to KIOCB_CANCELLED - * with xchg() or cmpxchg(), see batch_complete_aio() and kiocb_cancel(). - */ -#define KIOCB_CANCELLED ((void *) (~0ULL)) - struct aio_kiocb { union { struct kiocb rw; @@ -565,24 +552,18 @@ void kiocb_set_cancel_fn(struct kiocb *iocb, kiocb_cancel_fn *cancel) } EXPORT_SYMBOL(kiocb_set_cancel_fn); +/* + * Only cancel if there ws a ki_cancel function to start with, and we + * are the one how managed to clear it (to protect against simulatinious + * cancel calls). + */ static int kiocb_cancel(struct aio_kiocb *kiocb) { - kiocb_cancel_fn *old, *cancel; - - /* - * Don't want to set kiocb->ki_cancel = KIOCB_CANCELLED unless it - * actually has a cancel function, hence the cmpxchg() - */ - - cancel = READ_ONCE(kiocb->ki_cancel); - do { - if (!cancel || cancel == KIOCB_CANCELLED) - return -EINVAL; - - old = cancel; - cancel = cmpxchg(&kiocb->ki_cancel, old, KIOCB_CANCELLED); - } while (cancel != old); + kiocb_cancel_fn *cancel = kiocb->ki_cancel; + if (!cancel) + return -EINVAL; + kiocb->ki_cancel = NULL; return cancel(&kiocb->rw); } -- 2.14.2