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Message-Id: <1391189806-13319-4-git-send-email-davidlohr@hp.com>
Date: Fri, 31 Jan 2014 09:36:43 -0800
From: Davidlohr Bueso <davidlohr@...com>
To: akpm@...ux-foundation.org, iamjoonsoo.kim@....com
Cc: riel@...hat.com, mgorman@...e.de, mhocko@...e.cz,
aneesh.kumar@...ux.vnet.ibm.com, kamezawa.hiroyu@...fujitsu.com,
hughd@...gle.com, david@...son.dropbear.id.au, js1304@...il.com,
liwanp@...ux.vnet.ibm.com, n-horiguchi@...jp.nec.com,
dhillf@...il.com, rientjes@...gle.com, davidlohr@...com,
aswin@...com, scott.norton@...com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v2 3/6] mm, hugetlb: fix race in region tracking
From: Davidlohr Bueso <davidlohr@...com>
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 only the,
mmap_sem (exclusively). This doesn't prevent other tasks from modifying the
region structure, so it can be modified by two processes concurrently.
To solve this, introduce a spinlock to resv_map and make region manipulation
function grab it before they do actual work.
Acked-by: David Gibson <david@...son.dropbear.id.au>
Suggested-by: Joonsoo Kim <iamjoonsoo.kim@....com>
Signed-off-by: Davidlohr Bueso <davidlohr@...com>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
---
include/linux/hugetlb.h | 1 +
mm/hugetlb.c | 58 ++++++++++++++++++++++++++++++++-----------------
2 files changed, 39 insertions(+), 20 deletions(-)
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index f62c2f6..5b337cf 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -27,6 +27,7 @@ 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 dca03a6..3c03c7f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -135,15 +135,8 @@ static inline struct hugepage_subpool *subpool_vma(struct vm_area_struct *vma)
* Region tracking -- allows tracking of reservations and instantiated pages
* across the pages in a mapping.
*
- * The region data structures are protected by a combination of the mmap_sem
- * and the hugetlb_instantiation_mutex. To access or modify a region the caller
- * must either hold the mmap_sem for write, or the mmap_sem for read and
- * the hugetlb_instantiation_mutex:
- *
- * down_write(&mm->mmap_sem);
- * or
- * down_read(&mm->mmap_sem);
- * mutex_lock(&hugetlb_instantiation_mutex);
+ * The region data structures are embedded into a resv_map and
+ * protected by a resv_map's lock
*/
struct file_region {
struct list_head link;
@@ -156,6 +149,7 @@ static long region_add(struct resv_map *resv, long f, long t)
struct list_head *head = &resv->regions;
struct file_region *rg, *nrg, *trg;
+ spin_lock(&resv->lock);
/* Locate the region we are either in or before. */
list_for_each_entry(rg, head, link)
if (f <= rg->to)
@@ -185,15 +179,18 @@ static long region_add(struct resv_map *resv, long f, long t)
}
nrg->from = f;
nrg->to = t;
+ spin_unlock(&resv->lock);
return 0;
}
static long region_chg(struct resv_map *resv, long f, long t)
{
struct list_head *head = &resv->regions;
- struct file_region *rg, *nrg;
+ struct file_region *rg, *nrg = NULL;
long chg = 0;
+retry:
+ spin_lock(&resv->lock);
/* Locate the region we are before or in. */
list_for_each_entry(rg, head, link)
if (f <= rg->to)
@@ -203,15 +200,21 @@ static long region_chg(struct resv_map *resv, long f, long t)
* Subtle, allocate a new region at the position but make it zero
* size such that we can guarantee to record the reservation. */
if (&rg->link == head || t < rg->from) {
- nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
- if (!nrg)
- return -ENOMEM;
- nrg->from = f;
- nrg->to = f;
- INIT_LIST_HEAD(&nrg->link);
- list_add(&nrg->link, rg->link.prev);
+ if (!nrg) {
+ spin_unlock(&resv->lock);
+ nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
+ if (!nrg)
+ return -ENOMEM;
+
+ nrg->from = f;
+ nrg->to = f;
+ INIT_LIST_HEAD(&nrg->link);
+ goto retry;
+ }
- return t - f;
+ list_add(&nrg->link, rg->link.prev);
+ chg = t - f;
+ goto out_nrg;
}
/* Round our left edge to the current segment if it encloses us. */
@@ -224,7 +227,7 @@ static long region_chg(struct resv_map *resv, long f, long t)
if (&rg->link == head)
break;
if (rg->from > t)
- return chg;
+ goto out;
/* We overlap with this area, if it extends further than
* us then we must extend ourselves. Account for its
@@ -235,6 +238,14 @@ static long region_chg(struct resv_map *resv, long f, long t)
}
chg -= rg->to - rg->from;
}
+
+out:
+ spin_unlock(&resv->lock);
+ /* We already know we raced and no longer need the new region */
+ kfree(nrg);
+ return chg;
+out_nrg:
+ spin_unlock(&resv->lock);
return chg;
}
@@ -244,12 +255,13 @@ static long region_truncate(struct resv_map *resv, long end)
struct file_region *rg, *trg;
long chg = 0;
+ spin_lock(&resv->lock);
/* Locate the region we are either in or before. */
list_for_each_entry(rg, head, link)
if (end <= rg->to)
break;
if (&rg->link == head)
- return 0;
+ goto out;
/* If we are in the middle of a region then adjust it. */
if (end > rg->from) {
@@ -266,6 +278,9 @@ static long region_truncate(struct resv_map *resv, long end)
list_del(&rg->link);
kfree(rg);
}
+
+out:
+ spin_unlock(&resv->lock);
return chg;
}
@@ -275,6 +290,7 @@ static long region_count(struct resv_map *resv, long f, long t)
struct file_region *rg;
long chg = 0;
+ spin_lock(&resv->lock);
/* Locate each segment we overlap with, and count that overlap. */
list_for_each_entry(rg, head, link) {
long seg_from;
@@ -290,6 +306,7 @@ static long region_count(struct resv_map *resv, long f, long t)
chg += seg_to - seg_from;
}
+ spin_unlock(&resv->lock);
return chg;
}
@@ -387,6 +404,7 @@ struct resv_map *resv_map_alloc(void)
return NULL;
kref_init(&resv_map->refs);
+ spin_lock_init(&resv_map->lock);
INIT_LIST_HEAD(&resv_map->regions);
return resv_map;
--
1.8.1.4
--
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