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mm, hugetlb: fix race in region tracking 

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
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.

[davidlohr@hp.com: updated changelog]
Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Suggested-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Davidlohr Bueso 2014-04-03 14:47:27 -07:00 committed by Linus Torvalds
parent 1406ec9ba6
commit 7b24d8616b
2 changed files with 39 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/hugetlb.h
View File

@ -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);

58
mm/hugetlb.c
View File

@ -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;
return t - f;
nrg->from = f;
nrg->to = f;
INIT_LIST_HEAD(&nrg->link);
goto retry;
}
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;