From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx152.postini.com [74.125.245.152]) by kanga.kvack.org (Postfix) with SMTP id D0DB76B0031 for ; Tue, 30 Jul 2013 22:41:25 -0400 (EDT) Date: Wed, 31 Jul 2013 11:41:24 +0900 From: Joonsoo Kim Subject: Re: [PATCH 05/18] mm, hugetlb: protect region tracking via newly introduced resv_map lock Message-ID: <20130731024124.GC2548@lge.com> References: <1375075929-6119-1-git-send-email-iamjoonsoo.kim@lge.com> <1375075929-6119-6-git-send-email-iamjoonsoo.kim@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Hillf Danton Cc: Andrew Morton , Rik van Riel , Mel Gorman , Michal Hocko , "Aneesh Kumar K.V" , KAMEZAWA Hiroyuki , Hugh Dickins , Davidlohr Bueso , David Gibson , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Wanpeng Li , Naoya Horiguchi On Mon, Jul 29, 2013 at 04:58:57PM +0800, Hillf Danton wrote: > On Mon, Jul 29, 2013 at 1:31 PM, Joonsoo Kim wrote: > > There is a race condition if we map a same file on different processes. > > Region tracking is protected by mmap_sem and hugetlb_instantiation_mutex. > > When we do mmap, we don't grab a hugetlb_instantiation_mutex, but, > > grab a mmap_sem. This doesn't prevent other process to modify region > > structure, so it can be modified by two processes concurrently. > > > > To solve this, I introduce a lock to resv_map and make region manipulation > > function grab a lock before they do actual work. This makes region > > tracking safe. > > > > Signed-off-by: Joonsoo Kim > > > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > > index 2677c07..e29e28f 100644 > > --- a/include/linux/hugetlb.h > > +++ b/include/linux/hugetlb.h > > @@ -26,6 +26,7 @@ struct hugepage_subpool { > > > > struct resv_map { > > struct kref refs; > > + spinlock_t lock; > > struct list_head regions; > > }; > > extern struct resv_map *resv_map_alloc(void); > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > > index 24c0111..bf2ee11 100644 > > --- a/mm/hugetlb.c > > +++ b/mm/hugetlb.c > [...] > > @@ -193,6 +188,7 @@ static long region_chg(struct resv_map *resv, long f, long t) > > struct file_region *rg, *nrg; > > long chg = 0; > > > > + spin_lock(&resv->lock); > > /* Locate the region we are before or in. */ > > list_for_each_entry(rg, head, link) > > if (f <= rg->to) > > @@ -203,14 +199,18 @@ static long region_chg(struct resv_map *resv, long f, long t) > > * size such that we can guarantee to record the reservation. */ > > if (&rg->link == head || t < rg->from) { > > nrg = kmalloc(sizeof(*nrg), GFP_KERNEL); > > Hm, you are allocating a piece of memory with spin lock held. > How about replacing that spin lock with a mutex? I think that lock held period here is very short, so mutex is not appropriate to use. How about trying allocate with GFP_NOWAIT? And then if failed, release the lock and allocate with GFP_KERNEL and retry at the beginnig. Thanks. > > > - if (!nrg) > > - return -ENOMEM; > > + if (!nrg) { > > + chg = -ENOMEM; > > + goto out; > > + } > > + > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org