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@xxxxxxx> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 317b0a6..ee304d1 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 3e7a44b..cf0eaff 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 +200,23 @@ 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; + if (!nrg) { + spin_unlock(&resv->lock); + nrg = kmalloc(sizeof(*nrg), GFP_KERNEL); + if (!nrg) + return -ENOMEM; + + goto retry; + } + nrg->from = f; nrg->to = f; INIT_LIST_HEAD(&nrg->link); list_add(&nrg->link, rg->link.prev); + nrg = NULL; - return t - f; + chg = t - f; + goto out_locked; } /* Round our left edge to the current segment if it encloses us. */ @@ -224,7 +229,7 @@ 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_locked; /* We overlap with this area, if it extends further than * us then we must extend ourselves. Account for its @@ -235,6 +240,10 @@ static long region_chg(struct resv_map *resv, long f, long t) } chg -= rg->to - rg->from; } + +out_locked: + spin_unlock(&resv->lock); + kfree(nrg); return chg; } @@ -244,12 +253,13 @@ 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 +276,9 @@ 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 +288,7 @@ 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 +304,7 @@ 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 +402,7 @@ 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; -- 1.7.9.5 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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