Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755933AbZD3HbP (ORCPT ); Thu, 30 Apr 2009 03:31:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755975AbZD3Ham (ORCPT ); Thu, 30 Apr 2009 03:30:42 -0400 Received: from cantor2.suse.de ([195.135.220.15]:41265 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755044AbZD3Hak (ORCPT ); Thu, 30 Apr 2009 03:30:40 -0400 From: Nikanth Karthikesan Organization: Novell To: Andrew Morton , Jens Axboe Subject: [PATCH v2] Handle improbable possibility of io_context->refcount overflow Date: Thu, 30 Apr 2009 12:58:22 +0530 User-Agent: KMail/1.11.1 (Linux/2.6.27.21-0.1-default; KDE/4.2.1; x86_64; ; ) Cc: linux-kernel@vger.kernel.org References: <200904291221.40361.knikanth@novell.com> <200904291533.07377.knikanth@novell.com> <20090429081558.acaa2a9a.akpm@linux-foundation.org> In-Reply-To: <20090429081558.acaa2a9a.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200904301258.23182.knikanth@novell.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3592 Lines: 102 Currently io_context has an atomic_t(32-bit) as refcount. In case of cfq, for each device a task does I/O, a reference to the io_context would be taken. And when there are multiple process sharing io_contexts(CLONE_IO) would also have a reference to the same io_context. Theoretically the possible maximum number of processes sharing the same io_context + the number of disks/cfq_data referring to the same io_context can overflow the 32-bit counter on a very high-end machine. Even though it is an improbable case, let us make it difficult atleast on 64-bit architectures by changing the refcount to atomic_long_t. Signed-off-by: Nikanth Karthikesan --- diff --git a/block/blk-ioc.c b/block/blk-ioc.c index 012f065..d4ed600 100644 --- a/block/blk-ioc.c +++ b/block/blk-ioc.c @@ -35,9 +35,9 @@ int put_io_context(struct io_context *ioc) if (ioc == NULL) return 1; - BUG_ON(atomic_read(&ioc->refcount) == 0); + BUG_ON(atomic_long_read(&ioc->refcount) == 0); - if (atomic_dec_and_test(&ioc->refcount)) { + if (atomic_long_dec_and_test(&ioc->refcount)) { rcu_read_lock(); if (ioc->aic && ioc->aic->dtor) ioc->aic->dtor(ioc->aic); @@ -90,7 +90,7 @@ struct io_context *alloc_io_context(gfp_t gfp_flags, int node) ret = kmem_cache_alloc_node(iocontext_cachep, gfp_flags, node); if (ret) { - atomic_set(&ret->refcount, 1); + atomic_long_set(&ret->refcount, 1); atomic_set(&ret->nr_tasks, 1); spin_lock_init(&ret->lock); ret->ioprio_changed = 0; @@ -151,7 +151,7 @@ struct io_context *get_io_context(gfp_t gfp_flags, int node) ret = current_io_context(gfp_flags, node); if (unlikely(!ret)) break; - } while (!atomic_inc_not_zero(&ret->refcount)); + } while (!atomic_long_inc_not_zero(&ret->refcount)); return ret; } @@ -163,8 +163,8 @@ void copy_io_context(struct io_context **pdst, struct io_context **psrc) struct io_context *dst = *pdst; if (src) { - BUG_ON(atomic_read(&src->refcount) == 0); - atomic_inc(&src->refcount); + BUG_ON(atomic_long_read(&src->refcount) == 0); + atomic_long_inc(&src->refcount); put_io_context(dst); *pdst = src; } diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index a55a9bd..6a79c5b 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1282,7 +1282,7 @@ static void cfq_dispatch_request(struct cfq_data *cfqd, struct cfq_queue *cfqq) if (!cfqd->active_cic) { struct cfq_io_context *cic = RQ_CIC(rq); - atomic_inc(&cic->ioc->refcount); + atomic_long_inc(&cic->ioc->refcount); cfqd->active_cic = cic; } } diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h index 08b987b..dd05434 100644 --- a/include/linux/iocontext.h +++ b/include/linux/iocontext.h @@ -64,7 +64,7 @@ struct cfq_io_context { * and kmalloc'ed. These could be shared between processes. */ struct io_context { - atomic_t refcount; + atomic_long_t refcount; atomic_t nr_tasks; /* all the fields below are protected by this lock */ @@ -91,8 +91,8 @@ static inline struct io_context *ioc_task_link(struct io_context *ioc) * if ref count is zero, don't allow sharing (ioc is going away, it's * a race). */ - if (ioc && atomic_inc_not_zero(&ioc->refcount)) { - atomic_inc(&ioc->nr_tasks); + if (ioc && atomic_long_inc_not_zero(&ioc->refcount)) { + atomic_long_inc(&ioc->refcount); return ioc; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/