From: Ackerley Tng HugeTLB subpools currently only track used_hpages when the user configures a size limit. This is buggy since when there are existing allocations from the subpool that would have satisfied the minimum reservations, hugepage_subpool_put_pages() will still restore a reservation to the subpool. See below for an example of a false reservation. In addition, the subpool is considered free prematurely, is freed, and this ends up causing a use-after-free. The fix is to always track used_hpages within subpools, which is also beneficial in general because with that information, reservation tracking is also fully managed within hugepage_subpool_put_pages(). The subpool always knows how many pages were allocated through it. Every page allocated through the subpool increments used_hpages, regardless of whether a reservation was taken from it. Conceptually, now, every allocation involving a subpool uses a page from the subpool, which must be returned to the subpool. Every page taken from the subpool tries to use a subpool reservation. Restoring a page to the subpool reservations only if the page was taken from subpool reservations. (If used_hpages >= min_hpages, the page must have not have been taken from the reservations.) Always tracking used_hpages provides the subpool with information of both used and reserved counts to make the correct decision for both max_size and min_size correctly. With used_hpages always tracked, subpool_is_free() can be simplified, such that the subpool can be declared free if there are no more pages in use. Also update the + Documentation for used_hpages in the subpool struct, since it no longer matters whether the used pages count against the maximum. + Docstring for hugepage_subpool_{get,put}_pages + Documentation to use active voice, and remove some details in favor of having details documented in the docstring Also update statfs reporting. Previously, if max_hpages is negative, used_hpages is static at 0, so returning max_hpages - used_hpages returns -1 and is always correct. Now, if the subpool doesn't have a maximum requested size, indicate no limit for free pages (-1). If it does have a maximum size, report the difference between the requested size and the number of used pages. This difference is always positive, because if the mount does have a maximum size, hugepage_subpool_get_pages() ensures that the subpool usage never exceeds the maximum. Fixes: 1c5ecae3a93fa ("hugetlbfs: add minimum size accounting to subpools") Cc: stable@vger.kernel.org Signed-off-by: Ackerley Tng --- Documentation/mm/hugetlbfs_reserv.rst | 17 +---- .../translations/zh_CN/mm/hugetlbfs_reserv.rst | 11 +--- fs/hugetlbfs/inode.c | 8 ++- include/linux/hugetlb.h | 4 +- mm/hugetlb.c | 73 +++++++++++++--------- 5 files changed, 55 insertions(+), 58 deletions(-) diff --git a/Documentation/mm/hugetlbfs_reserv.rst b/Documentation/mm/hugetlbfs_reserv.rst index a49115db18c76..d244583fdcbc3 100644 --- a/Documentation/mm/hugetlbfs_reserv.rst +++ b/Documentation/mm/hugetlbfs_reserv.rst @@ -314,21 +314,8 @@ huge pages. If they can not be reserved, the mount fails. The routines hugepage_subpool_get/put_pages() are called when pages are obtained from or released back to a subpool. They perform all subpool accounting, and track any reservations associated with the subpool. -hugepage_subpool_get/put_pages are passed the number of huge pages by which -to adjust the subpool 'used page' count (down for get, up for put). Normally, -they return the same value that was passed or an error if not enough pages -exist in the subpool. - -However, if reserves are associated with the subpool a return value less -than the passed value may be returned. This return value indicates the -number of additional global pool adjustments which must be made. For example, -suppose a subpool contains 3 reserved huge pages and someone asks for 5. -The 3 reserved pages associated with the subpool can be used to satisfy part -of the request. But, 2 pages must be obtained from the global pools. To -relay this information to the caller, the value 2 is returned. The caller -is then responsible for attempting to obtain the additional two pages from -the global pools. - +hugepage_subpool_get/put_pages() use the number of huge pages passed to adjust +the subpool 'used page' count. COW and Reservations ==================== diff --git a/Documentation/translations/zh_CN/mm/hugetlbfs_reserv.rst b/Documentation/translations/zh_CN/mm/hugetlbfs_reserv.rst index 20947f8bd0654..ae1f1f31477fc 100644 --- a/Documentation/translations/zh_CN/mm/hugetlbfs_reserv.rst +++ b/Documentation/translations/zh_CN/mm/hugetlbfs_reserv.rst @@ -246,15 +246,8 @@ hugepage_subpool的min_hpages字段中被跟踪。在挂载时，hugetlb_acct_me 被调用以预留指定数量的巨页。如果它们不能被预留，挂载就会失败。 当从子池中获取或释放页面时，会调用hugepage_subpool_get/put_pages()函数。 -hugepage_subpool_get/put_pages被传递给巨页数量，以此来调整子池的 “已用页面” 计数 -（get为下降，put为上升）。通常情况下，如果子池中没有足够的页面，它们会返回与传递的相同的值或 -一个错误。 - -然而，如果预留与子池相关联，可能会返回一个小于传递值的返回值。这个返回值表示必须进行的额外全局 -池调整的数量。例如，假设一个子池包含3个预留的巨页，有人要求5个。与子池相关的3个预留页可以用来 -满足部分请求。但是，必须从全局池中获得2个页面。为了向调用者转达这一信息，将返回值2。然后，调用 -者要负责从全局池中获取另外两个页面。 - +它们负责所有子池的统计核算，并跟踪与子池相关联的预留。 +hugepage_subpool_get/put_pages()函数使用传入的巨页数量来调整子池的“已用页面”计数。 COW和预留 ========== diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 7611a8470ea26..5113f743f6fc7 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -1109,8 +1109,12 @@ static int hugetlbfs_statfs(struct dentry *dentry, struct kstatfs *buf) spin_lock_irq(&sbinfo->spool->lock); buf->f_blocks = sbinfo->spool->max_hpages; - free_pages = sbinfo->spool->max_hpages - - sbinfo->spool->used_hpages; + if (sbinfo->spool->max_hpages == -1) { + free_pages = -1; + } else { + free_pages = sbinfo->spool->max_hpages - + sbinfo->spool->used_hpages; + } buf->f_bavail = buf->f_bfree = free_pages; spin_unlock_irq(&sbinfo->spool->lock); buf->f_files = sbinfo->max_inodes; diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 16c4c4caa126c..4551ff3023640 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -39,8 +39,8 @@ struct hugepage_subpool { spinlock_t lock; long count; long max_hpages; /* Maximum huge pages or -1 if no maximum. */ - long used_hpages; /* Used count against maximum, includes */ - /* both allocated and reserved pages. */ + long used_hpages; /* Used page count, includes both */ + /* allocated and reserved pages. */ struct hstate *hstate; long min_hpages; /* Minimum huge pages or -1 if no minimum. */ long rsv_hpages; /* Pages reserved against global pool to */ diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 7857728457952..66b6601abb069 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -130,12 +130,8 @@ static inline bool subpool_is_free(struct hugepage_subpool *spool) { if (spool->count) return false; - if (spool->max_hpages != -1) - return spool->used_hpages == 0; - if (spool->min_hpages != -1) - return spool->rsv_hpages == spool->min_hpages; - return true; + return spool->used_hpages == 0; } static inline void unlock_or_release_subpool(struct hugepage_subpool *spool, @@ -193,13 +189,18 @@ void hugepage_put_subpool(struct hugepage_subpool *spool) unlock_or_release_subpool(spool, flags); } -/* - * Subpool accounting for allocating and reserving pages. - * Return -ENOMEM if there are not enough resources to satisfy the - * request. Otherwise, return the number of pages by which the - * global pools must be adjusted (upward). The returned value may - * only be different than the passed value (delta) in the case where - * a subpool minimum size must be maintained. +/** + * hugepage_subpool_get_pages - Get pages from a subpool + * @spool: pointer to subpool structure (may be NULL) + * @delta: number of pages to allocate or reserve + * + * Check and update subpool page usage counts when allocating or + * reserving @delta hugepages. + * + * Context: Takes spool->lock using spin_lock_irq(). + * Return: Non-negative number of reservations that cannot be + * satisfied by the subpool, or -ENOMEM if the subpool maximum + * limit would be exceeded. */ static long hugepage_subpool_get_pages(struct hugepage_subpool *spool, long delta) @@ -211,15 +212,14 @@ static long hugepage_subpool_get_pages(struct hugepage_subpool *spool, spin_lock_irq(&spool->lock); - if (spool->max_hpages != -1) { /* maximum size accounting */ - if ((spool->used_hpages + delta) <= spool->max_hpages) - spool->used_hpages += delta; - else { - ret = -ENOMEM; - goto unlock_ret; - } + if (spool->max_hpages != -1 && + spool->used_hpages + delta > spool->max_hpages) { + ret = -ENOMEM; + goto unlock_ret; } + spool->used_hpages += delta; + /* minimum size accounting */ if (spool->min_hpages != -1 && spool->rsv_hpages) { if (delta > spool->rsv_hpages) { @@ -240,11 +240,19 @@ static long hugepage_subpool_get_pages(struct hugepage_subpool *spool, return ret; } -/* - * Subpool accounting for freeing and unreserving pages. - * Return the number of global page reservations that must be dropped. - * The return value may only be different than the passed value (delta) - * in the case where a subpool minimum size must be maintained. +/** + * hugepage_subpool_put_pages - Release pages back to a subpool + * @spool: pointer to subpool structure (may be NULL) + * @delta: number of pages to free or unreserve + * + * Check and update subpool page usage counts when freeing or + * unreserving @delta hugepages. + * + * Context: Takes spool->lock using spin_lock_irqsave(). May release + * and free @spool if its usage count and references reach + * zero. + * Return: Non-negative number of reservations that the subpool cannot + * absorb. */ static long hugepage_subpool_put_pages(struct hugepage_subpool *spool, long delta) @@ -257,19 +265,24 @@ static long hugepage_subpool_put_pages(struct hugepage_subpool *spool, spin_lock_irqsave(&spool->lock, flags); - if (spool->max_hpages != -1) /* maximum size accounting */ - spool->used_hpages -= delta; + spool->used_hpages -= delta; /* minimum size accounting */ if (spool->min_hpages != -1 && spool->used_hpages < spool->min_hpages) { - if (spool->rsv_hpages + delta <= spool->min_hpages) + /* + * limit is the maximum number of reservations that + * can be restored to this subpool. + */ + long limit = spool->min_hpages - spool->used_hpages; + + if (spool->rsv_hpages + delta <= limit) ret = 0; else - ret = spool->rsv_hpages + delta - spool->min_hpages; + ret = spool->rsv_hpages + delta - limit; spool->rsv_hpages += delta; - if (spool->rsv_hpages > spool->min_hpages) - spool->rsv_hpages = spool->min_hpages; + if (spool->rsv_hpages > limit) + spool->rsv_hpages = limit; } /* -- 2.55.0.970.g62bdec98f9-goog