From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-2684081-1520286156-2-5401446996738894751 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 0.249, 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='CN', 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=1520286156; b=HJaUexyqN31rSRE2ykHOoPRaQv8Q97rxzHEo745hX4WTdeb SkNboGV1XECltGDi7x6D3ZNU5cOOjsi+6cDZ3VCLb8Mpa5EZC71hCldpI2KCu53o YOVCXsEso9WbRQp2BalZSh8UIr7o6Coz1Zl71cOMWduDF3ZqH+ggWhK38B3LVzuO rsPeCo2dw18bERlt4qXJW0RSHie/Mpkt7hN+kpOgRLd7MboCxoBVUzOhUUFTcp+K 93Gi+2I62EnL77hmuZOAv9VNAce/jk5MTHSnoNwLtXyypHS7QtLp0vecZ7aHKmGt 73X64cG8ThhvhQHbjUP9PhXXJAjwUJtly5veXJQ== 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=1520286156; bh=8tobXlXxyQZbJkdjl3yVb2Bh3VaOvmlK+hRnKh1paw0=; b=K46q9YjNHIlR Zh3/Uy45oyV7TAKir+YnyeiXcCRDquDCrfE7Xivm2U26jycr/OvRVdrB9JMVndbI gCYfAUdqCAjBQdEZr2uV7IMp/hf4AtSiBWQBV/t/1/ANgwvkeV/fpEfeg7ovi2Bl l32GGFea7+7/AedzOLSBEayWgST5eLm5S0UJzSswHSChYiN4ImDCiRv49aXsa5I5 aPNy4UsorTmxaTfmfNB4XIEajsAcNHEQhPhNyQx8atxVH3jPweYqDfojfNLyvN25 Us2wVa6GgHy89rYJBcHVkCM4Kp1EBAioTOSQIIqJ/Sil/1CaG0vCwkbM9ynI+aSU DpmJXp0XWA== 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=pvsDE482 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-category=clean score=0 state=0; 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=pvsDE482 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-category=clean score=0 state=0; 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 S933213AbeCEVkE (ORCPT ); Mon, 5 Mar 2018 16:40:04 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:60614 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932314AbeCEV1u (ORCPT ); Mon, 5 Mar 2018 16:27:50 -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: Mon, 5 Mar 2018 13:27:12 -0800 Message-Id: <20180305212743.16664-6-hch@lst.de> X-Mailer: git-send-email 2.14.2 In-Reply-To: <20180305212743.16664-1-hch@lst.de> References: <20180305212743.16664-1-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