Messages in this thread | | | 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 |
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On Mon, Jul 29, 2013 at 04:58:57PM +0800, Hillf Danton wrote: > On Mon, Jul 29, 2013 at 1:31 PM, Joonsoo Kim <iamjoonsoo.kim@lge.com> 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 <iamjoonsoo.kim@lge.com> > > > > 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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
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