From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752786AbaCJING (ORCPT ); Mon, 10 Mar 2014 04:13:06 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:48326 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752535AbaCJIND (ORCPT ); Mon, 10 Mar 2014 04:13:03 -0400 X-IronPort-AV: E=Sophos;i="4.97,622,1389715200"; d="scan'208";a="9670975" From: Tang Chen To: viro@zeniv.linux.org.uk, bcrl@kvack.org, jmoyer@redhat.com, kosaki.motohiro@gmail.com, kosaki.motohiro@jp.fujitsu.com, isimatu.yasuaki@jp.fujitsu.com Cc: guz.fnst@cn.fujitsu.com, linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, linux-kernel@vger.kernel.org, miaox@cn.fujitsu.com Subject: [RESEND v2 PATCH 1/2] aio, memory-hotplug: Fix confliction when migrating and accessing ring pages. Date: Mon, 10 Mar 2014 16:15:33 +0800 Message-Id: <1394439334-28523-2-git-send-email-tangchen@cn.fujitsu.com> X-Mailer: git-send-email 1.7.11.7 In-Reply-To: <1394439334-28523-1-git-send-email-tangchen@cn.fujitsu.com> References: <1394439334-28523-1-git-send-email-tangchen@cn.fujitsu.com> X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2014/03/10 16:10:03, Serialize by Router on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2014/03/10 16:10:11, Serialize complete at 2014/03/10 16:10:11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org IO ring page migration has been implemented by the following patch: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/fs/aio.c?id=36bc08cc01709b4a9bb563b35aa530241ddc63e3 In this patch, ctx->completion_lock is used to prevent other processes from accessing the ring page being migrated. But in aio_setup_ring(), ioctx_add_table() and aio_read_events_ring(), when writing to the ring page, they didn't take ctx->completion_lock. As a result, for example, we have the following problem: thread 1 | thread 2 | aio_migratepage() | |-> take ctx->completion_lock | |-> migrate_page_copy(new, old) | | *NOW*, ctx->ring_pages[idx] == old | | | *NOW*, ctx->ring_pages[idx] == old | aio_read_events_ring() | |-> ring = kmap_atomic(ctx->ring_pages[0]) | |-> ring->head = head; *HERE, write to the old ring page* | |-> kunmap_atomic(ring); | |-> ctx->ring_pages[idx] = new | | *BUT NOW*, the content of | | ring_pages[idx] is old. | |-> release ctx->completion_lock | As above, the new ring page will not be updated. The solution is taking ctx->completion_lock in thread 2, which means, in aio_setup_ring(), ioctx_add_table() and aio_read_events_ring() when writing to ring pages. Reported-by: Yasuaki Ishimatsu Reviewed-by: Jeff Moyer Signed-off-by: Tang Chen --- v2: Use spin_lock_irq rather than spin_lock_irqsave as Jeff suggested. --- fs/aio.c | 28 ++++++++++++++++++++++++++++ 1 files changed, 28 insertions(+), 0 deletions(-) diff --git a/fs/aio.c b/fs/aio.c index 062a5f6..dc70246 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -437,6 +437,14 @@ static int aio_setup_ring(struct kioctx *ctx) ctx->user_id = ctx->mmap_base; ctx->nr_events = nr_events; /* trusted copy */ + /* + * The aio ring pages are user space pages, so they can be migrated. + * When writing to an aio ring page, we should ensure the page is not + * being migrated. Aio page migration procedure is protected by + * ctx->completion_lock, so we add this lock here. + */ + spin_lock_irq(&ctx->completion_lock); + ring = kmap_atomic(ctx->ring_pages[0]); ring->nr = nr_events; /* user copy */ ring->id = ~0U; @@ -448,6 +456,8 @@ static int aio_setup_ring(struct kioctx *ctx) kunmap_atomic(ring); flush_dcache_page(ctx->ring_pages[0]); + spin_unlock_irq(&ctx->completion_lock); + return 0; } @@ -556,9 +566,17 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm) rcu_read_unlock(); spin_unlock(&mm->ioctx_lock); + /* + * Accessing ring pages must be done + * holding ctx->completion_lock to + * prevent aio ring page migration + * procedure from migrating ring pages. + */ + spin_lock_irq(&ctx->completion_lock); ring = kmap_atomic(ctx->ring_pages[0]); ring->id = ctx->id; kunmap_atomic(ring); + spin_unlock_irq(&ctx->completion_lock); return 0; } @@ -1066,11 +1084,21 @@ static long aio_read_events_ring(struct kioctx *ctx, head %= ctx->nr_events; } + /* + * The aio ring pages are user space pages, so they can be migrated. + * When writing to an aio ring page, we should ensure the page is not + * being migrated. Aio page migration procedure is protected by + * ctx->completion_lock, so we add this lock here. + */ + spin_lock_irq(&ctx->completion_lock); + ring = kmap_atomic(ctx->ring_pages[0]); ring->head = head; kunmap_atomic(ring); flush_dcache_page(ctx->ring_pages[0]); + spin_unlock_irq(&ctx->completion_lock); + pr_debug("%li h%u t%u\n", ret, head, tail); put_reqs_available(ctx, ret); -- 1.7.7