From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-3264303-1522272924-2-1161933591418594286 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, ME_NOAUTH 0.01, 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='uk', MailFrom='org' X-Spam-charsets: plain='us-ascii' 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=1522272923; b=UIQTPU5edSuODYzNZ3+HmNG34ngq4WIqtzzczlS8CqJXuny YT+jCYkiS12lPajPjd8CqRfQTIV+jbUgE8VoqdONVp3Qi68HsZDuvFTNXrAPBidb BE1TTpLe8xtzE6wJp9eOypjRtKuvyGnjxs4KinqNuzT7oCbWTfpJ0n9s4sGEwFaJ XOdLRzagreCHfoxS+AKroxtRH40lM67wPhjIm4OHevmk++WI8zR598ycYX4DrCrB /1wt8D4JDqKKxqzju4hRD0ymrTpOm43JrlD/9e/eJ7ncsV+QY4Yq44EK7pblzM5Z WXB2s0c/zDvZj/VaXSmoTn2n+/Bw/emAmiPtqIQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=date:from:to:cc:subject:message-id :references:mime-version:content-type:in-reply-to:sender :list-id; s=arctest; t=1522272923; bh=f8VJe1xWcaX/Xx/qE8G3ata9as boiyUkWvRudjvLNso=; b=OAZasZ/1Yx6WJcYf8dGvY6/XNB/bbF/DG+N335dpr/ b8a720JDy3PEeyLLSsKfHKLnR0pGtGSZ8Jocs3O6noOor7ym2cIQ0x8OIXKS0YWs tOYBbOi/IBsL9aue1IC8UxEvSVslfMIJ1yTY5yhSO6qe/F9WDhadMKCQ8hu30yQn io8AHzPEE0NxTzgSTVTD7vahTJQ8AKkyqhsmQIYWquF7WYoMNSh55B/3txMl5ouC 2Wr+NK8kStDNOLfaGUZ+XSjfjYjym2UBlUGfuNTWbL3bLjwiqPrU0h11u5xInWEg wCyTZzgsn/QbDJXUF8K9AOJnssUD14lqgT38opSVwrXQ== ARC-Authentication-Results: i=1; mx4.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,has-list-id=yes,d=none) header.from=zeniv.linux.org.uk; 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-cm=none score=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=zeniv.linux.org.uk header.mx.error=NOERROR header.result=warn header_org.domain=linux.org.uk header_org.result=pass header_is_org_domain=no; x-vs=clean score=-100 state=0 Authentication-Results: mx4.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,has-list-id=yes,d=none) header.from=zeniv.linux.org.uk; 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-cm=none score=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=zeniv.linux.org.uk header.mx.error=NOERROR header.result=warn header_org.domain=linux.org.uk header_org.result=pass header_is_org_domain=no; x-vs=clean score=-100 state=0 X-ME-VSCategory: clean X-CM-Envelope: MS4wfLkt37nv0U4A7hyr82Di1+k+rM4twF8eoJYR9sPWCbazqP7kGK9btoe9GUNSriHRxlYh250s+jM1ehpF7k4AhkQ/kTEhOSPY99dzbCO46MjffiJYQe4p bHKHAPqlSW6izapLXCgB5Wzn4LYvH9pMXulec7hec0t/R7yK8exr3z2VGR7m3CgsmivJLDd/iWPsEinJikH4AtFh1hIVTSGOvyUKrLMz8Xy+cNeD0UG2vD+k X-CM-Analysis: v=2.3 cv=JLoVTfCb c=1 sm=1 tr=0 a=UK1r566ZdBxH71SXbqIOeA==:117 a=UK1r566ZdBxH71SXbqIOeA==:17 a=kj9zAlcOel0A:10 a=v2DPQv5-lfwA:10 a=VwQbUJbxAAAA:8 a=gNQtK-quL3SsdyW9mKQA:9 a=CjuIK1q_8ugA:10 a=x8gzFH9gYPwA:10 a=AjGcO6oz07-iQ99wixmX:22 X-ME-CMScore: 0 X-ME-CMCategory: none Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753392AbeC1VfE (ORCPT ); Wed, 28 Mar 2018 17:35:04 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:43522 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753117AbeC1VfD (ORCPT ); Wed, 28 Mar 2018 17:35:03 -0400 Date: Wed, 28 Mar 2018 22:34:59 +0100 From: Al Viro To: Christoph Hellwig 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: Re: [PATCH 07/30] aio: add delayed cancel support Message-ID: <20180328213459.GW30522@ZenIV.linux.org.uk> References: <20180328072926.17131-1-hch@lst.de> <20180328072926.17131-8-hch@lst.de> <20180328163526.GV30522@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180328163526.GV30522@ZenIV.linux.org.uk> User-Agent: Mutt/1.9.1 (2017-09-22) 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: On Wed, Mar 28, 2018 at 05:35:26PM +0100, Al Viro wrote: > On Wed, Mar 28, 2018 at 09:29:03AM +0200, Christoph Hellwig wrote: > > static void aio_fsync_work(struct work_struct *work) > > { > > struct fsync_iocb *req = container_of(work, struct fsync_iocb, work); > > + struct aio_kiocb *iocb = container_of(req, struct aio_kiocb, fsync); > > + struct file *file = req->file; > > int ret; > > > > ret = vfs_fsync(req->file, req->datasync); > > - fput(req->file); > > - aio_complete(container_of(req, struct aio_kiocb, fsync), ret, 0); > > + if (aio_complete(iocb, ret, 0, 0)) > > + fput(file); > > IDGI. > 1) can aio_complete() ever return false here? > 2) do we ever have aio_kiocb that would not have an associated > struct file * that needs to be dropped on successful aio_complete()? AFAICS, > rw, fsync and poll variants all have one, and I'm not sure what kind of > async IO *could* be done without an opened file. OK, hell with that. I've tried to play with turning kiocb into a struct with anon union in it, with poll and fsync parts folded into that sucker and ki_filp lifted into common part. Possible, but it's hairy as hell and can be done afterwards. However, doing that digging has turned up something really nasty. Look: in io_cancel(2) you have spin_lock_irq(&ctx->ctx_lock); kiocb = lookup_kiocb(ctx, iocb, key); if (kiocb) { if (kiocb->flags & AIO_IOCB_DELAYED_CANCEL) { kiocb->flags |= AIO_IOCB_CANCELLED; } else { ret = kiocb_cancel(kiocb); kiocb = NULL; } } spin_unlock_irq(&ctx->ctx_lock); Now, suppose two threads call io_cancel() on the same aio_poll in progress. Both hit that code and *both* find the same kiocb. Sure, the first one will shortly do if (kiocb) ret = kiocb_cancel(kiocb); which will remove it from the list. Too late, though - you've already dropped ->ctx_lock, letting the second one find it. Result: two aio_poll_cancel() in parallel, with resulting double-free and double-fput(). You really need to remove it from the ->active_reqs before dropping the lock. free_ioctx_users() does it correctly, io_cancel(2) fucks it up. I'd add something like struct aio_kiocb *kiocb_cancel_locked(struct aio_kiocb *kiocb) { if (!kiocb) return ERR_PTR(-EINVAL); if (kiocb->flags & AIO_IOCB_DELAYED_CANCEL) { list_del(&kiocb->ki_list); kiocb->flags |= AIO_IOCB_CANCELLED; return kiocb; } else { return ERR_PTR(kiocb_cancel(kiocb)); } } with spin_lock_irq(&ctx->ctx_lock); while (!list_empty(&ctx->active_reqs)) { req = list_first_entry(&ctx->active_reqs, struct aio_kiocb, ki_list); req = kiocb_cancel_locked(req); if (!IS_ERR_OR_NULL(req)) list_add_tail(&req->ki_list, &list); } spin_unlock_irq(&ctx->ctx_lock); in free_ioctx_users() and spin_lock_irq(&ctx->ctx_lock); kiocb = kiocb_cancel_locked(lookup_kiocb(ctx, iocb, key)); spin_unlock_irq(&ctx->ctx_lock); ret = IS_ERR_OR_NULL(kiocb) ? PTR_ERR(kiocb) : kiocb_cancel(kiocb); in io_cancel(2)...