[PATCH v2 7/8] hugetlb: make free_huge_page irq safe

[Mike Kravetz]

Commit c77c0a8ac4c5 ("mm/hugetlb: defer freeing of huge pages if in
non-task context") was added to address the issue of free_huge_page
being called from irq context.  That commit hands off free_huge_page
processing to a workqueue if !in_task.  However, this doesn't cover
all the cases as pointed out by 0day bot lockdep report [1].

:  Possible interrupt unsafe locking scenario:
:
:        CPU0                    CPU1
:        ----                    ----
:   lock(hugetlb_lock);
:                                local_irq_disable();
:                                lock(slock-AF_INET);
:                                lock(hugetlb_lock);
:   <Interrupt>
:     lock(slock-AF_INET);

Shakeel has later explained that this is very likely TCP TX zerocopy
from hugetlb pages scenario when the networking code drops a last
reference to hugetlb page while having IRQ disabled. Hugetlb freeing
path doesn't disable IRQ while holding hugetlb_lock so a lock dependency
chain can lead to a deadlock.

This commit addresses the issue by doing the following:
- Make hugetlb_lock irq safe.  This is mostly a simple process of
  changing spin_*lock calls to spin_*lock_irq* calls.
- Make subpool lock irq safe in a similar manner.
- Revert the !in_task check and workqueue handoff.

[1] https://lore.kernel.org/linux-mm/000000000000f1c03b05bc43aadc@xxxxxxxxxx/

Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 mm/hugetlb.c        | 167 ++++++++++++++++----------------------------
 mm/hugetlb_cgroup.c |   8 +--
 2 files changed, 66 insertions(+), 109 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index d3f3cb8766b8..bf36abc2305a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -93,9 +93,10 @@ static inline bool subpool_is_free(struct hugepage_subpool *spool)
 	return true;
 }
 
-static inline void unlock_or_release_subpool(struct hugepage_subpool *spool)
+static inline void unlock_or_release_subpool(struct hugepage_subpool *spool,
+						unsigned long irq_flags)
 {
-	spin_unlock(&spool->lock);
+	spin_unlock_irqrestore(&spool->lock, irq_flags);
 
 	/* If no pages are used, and no other handles to the subpool
 	 * remain, give up any reservations based on minimum size and
@@ -134,10 +135,12 @@ struct hugepage_subpool *hugepage_new_subpool(struct hstate *h, long max_hpages,
 
 void hugepage_put_subpool(struct hugepage_subpool *spool)
 {
-	spin_lock(&spool->lock);
+	unsigned long flags;
+
+	spin_lock_irqsave(&spool->lock, flags);
 	BUG_ON(!spool->count);
 	spool->count--;
-	unlock_or_release_subpool(spool);
+	unlock_or_release_subpool(spool, flags);
 }
 
 /*
@@ -156,7 +159,7 @@ static long hugepage_subpool_get_pages(struct hugepage_subpool *spool,
 	if (!spool)
 		return ret;
 
-	spin_lock(&spool->lock);
+	spin_lock_irq(&spool->lock);
 
 	if (spool->max_hpages != -1) {		/* maximum size accounting */
 		if ((spool->used_hpages + delta) <= spool->max_hpages)
@@ -183,7 +186,7 @@ static long hugepage_subpool_get_pages(struct hugepage_subpool *spool,
 	}
 
 unlock_ret:
-	spin_unlock(&spool->lock);
+	spin_unlock_irq(&spool->lock);
 	return ret;
 }
 
@@ -197,11 +200,12 @@ static long hugepage_subpool_put_pages(struct hugepage_subpool *spool,
 				       long delta)
 {
 	long ret = delta;
+	unsigned long flags;
 
 	if (!spool)
 		return delta;
 
-	spin_lock(&spool->lock);
+	spin_lock_irqsave(&spool->lock, flags);
 
 	if (spool->max_hpages != -1)		/* maximum size accounting */
 		spool->used_hpages -= delta;
@@ -222,7 +226,7 @@ static long hugepage_subpool_put_pages(struct hugepage_subpool *spool,
 	 * If hugetlbfs_put_super couldn't free spool due to an outstanding
 	 * quota reference, free it now.
 	 */
-	unlock_or_release_subpool(spool);
+	unlock_or_release_subpool(spool, flags);
 
 	return ret;
 }
@@ -1412,7 +1416,7 @@ struct hstate *size_to_hstate(unsigned long size)
 	return NULL;
 }
 
-static void __free_huge_page(struct page *page)
+void free_huge_page(struct page *page)
 {
 	/*
 	 * Can't pass hstate in here because it is called from the
@@ -1422,6 +1426,7 @@ static void __free_huge_page(struct page *page)
 	int nid = page_to_nid(page);
 	struct hugepage_subpool *spool = hugetlb_page_subpool(page);
 	bool restore_reserve;
+	unsigned long flags;
 
 	VM_BUG_ON_PAGE(page_count(page), page);
 	VM_BUG_ON_PAGE(page_mapcount(page), page);
@@ -1450,7 +1455,7 @@ static void __free_huge_page(struct page *page)
 			restore_reserve = true;
 	}
 
-	spin_lock(&hugetlb_lock);
+	spin_lock_irqsave(&hugetlb_lock, flags);
 	ClearHPageMigratable(page);
 	hugetlb_cgroup_uncharge_page(hstate_index(h),
 				     pages_per_huge_page(h), page);
@@ -1461,67 +1466,19 @@ static void __free_huge_page(struct page *page)
 
 	if (HPageTemporary(page)) {
 		remove_hugetlb_page(h, page, false);
-		spin_unlock(&hugetlb_lock);
+		spin_unlock_irqrestore(&hugetlb_lock, flags);
 		update_and_free_page(h, page);
 	} else if (h->surplus_huge_pages_node[nid]) {
 		/* remove the page from active list */
 		remove_hugetlb_page(h, page, true);
-		spin_unlock(&hugetlb_lock);
+		spin_unlock_irqrestore(&hugetlb_lock, flags);
 		update_and_free_page(h, page);
 	} else {
 		arch_clear_hugepage_flags(page);
 		enqueue_huge_page(h, page);
-		spin_unlock(&hugetlb_lock);
-	}
-}
-
-/*
- * As free_huge_page() can be called from a non-task context, we have
- * to defer the actual freeing in a workqueue to prevent potential
- * hugetlb_lock deadlock.
- *
- * free_hpage_workfn() locklessly retrieves the linked list of pages to
- * be freed and frees them one-by-one. As the page->mapping pointer is
- * going to be cleared in __free_huge_page() anyway, it is reused as the
- * llist_node structure of a lockless linked list of huge pages to be freed.
- */
-static LLIST_HEAD(hpage_freelist);
-
-static void free_hpage_workfn(struct work_struct *work)
-{
-	struct llist_node *node;
-	struct page *page;
-
-	node = llist_del_all(&hpage_freelist);
-
-	while (node) {
-		page = container_of((struct address_space **)node,
-				     struct page, mapping);
-		node = node->next;
-		__free_huge_page(page);
+		spin_unlock_irqrestore(&hugetlb_lock, flags);
 	}
 }
-static DECLARE_WORK(free_hpage_work, free_hpage_workfn);
-
-void free_huge_page(struct page *page)
-{
-	/*
-	 * Defer freeing if in non-task context to avoid hugetlb_lock deadlock.
-	 */
-	if (!in_task()) {
-		/*
-		 * Only call schedule_work() if hpage_freelist is previously
-		 * empty. Otherwise, schedule_work() had been called but the
-		 * workfn hasn't retrieved the list yet.
-		 */
-		if (llist_add((struct llist_node *)&page->mapping,
-			      &hpage_freelist))
-			schedule_work(&free_hpage_work);
-		return;
-	}
-
-	__free_huge_page(page);
-}
 
 static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
 {
@@ -1530,11 +1487,11 @@ static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
 	hugetlb_set_page_subpool(page, NULL);
 	set_hugetlb_cgroup(page, NULL);
 	set_hugetlb_cgroup_rsvd(page, NULL);
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 	h->nr_huge_pages++;
 	h->nr_huge_pages_node[nid]++;
 	ClearHPageFreed(page);
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 }
 
 static void prep_compound_gigantic_page(struct page *page, unsigned int order)
@@ -1780,7 +1737,7 @@ int dissolve_free_huge_page(struct page *page)
 	if (!PageHuge(page))
 		return 0;
 
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 	if (!PageHuge(page)) {
 		rc = 0;
 		goto out;
@@ -1797,7 +1754,7 @@ int dissolve_free_huge_page(struct page *page)
 		 * when it is dissolved.
 		 */
 		if (unlikely(!HPageFreed(head))) {
-			spin_unlock(&hugetlb_lock);
+			spin_unlock_irq(&hugetlb_lock);
 			cond_resched();
 
 			/*
@@ -1821,12 +1778,12 @@ int dissolve_free_huge_page(struct page *page)
 		}
 		remove_hugetlb_page(h, page, false);
 		h->max_huge_pages--;
-		spin_unlock(&hugetlb_lock);
+		spin_unlock_irq(&hugetlb_lock);
 		update_and_free_page(h, head);
 		return 0;
 	}
 out:
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 	return rc;
 }
 
@@ -1868,16 +1825,16 @@ static struct page *alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask,
 	if (hstate_is_gigantic(h))
 		return NULL;
 
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 	if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages)
 		goto out_unlock;
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 
 	page = alloc_fresh_huge_page(h, gfp_mask, nid, nmask, NULL);
 	if (!page)
 		return NULL;
 
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 	/*
 	 * We could have raced with the pool size change.
 	 * Double check that and simply deallocate the new page
@@ -1887,7 +1844,7 @@ static struct page *alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask,
 	 */
 	if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages) {
 		SetHPageTemporary(page);
-		spin_unlock(&hugetlb_lock);
+		spin_unlock_irq(&hugetlb_lock);
 		put_page(page);
 		return NULL;
 	} else {
@@ -1896,7 +1853,7 @@ static struct page *alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask,
 	}
 
 out_unlock:
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 
 	return page;
 }
@@ -1946,17 +1903,17 @@ struct page *alloc_buddy_huge_page_with_mpol(struct hstate *h,
 struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
 		nodemask_t *nmask, gfp_t gfp_mask)
 {
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 	if (h->free_huge_pages - h->resv_huge_pages > 0) {
 		struct page *page;
 
 		page = dequeue_huge_page_nodemask(h, gfp_mask, preferred_nid, nmask);
 		if (page) {
-			spin_unlock(&hugetlb_lock);
+			spin_unlock_irq(&hugetlb_lock);
 			return page;
 		}
 	}
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 
 	return alloc_migrate_huge_page(h, gfp_mask, preferred_nid, nmask);
 }
@@ -2004,7 +1961,7 @@ static int gather_surplus_pages(struct hstate *h, long delta)
 
 	ret = -ENOMEM;
 retry:
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 	for (i = 0; i < needed; i++) {
 		page = alloc_surplus_huge_page(h, htlb_alloc_mask(h),
 				NUMA_NO_NODE, NULL);
@@ -2021,7 +1978,7 @@ static int gather_surplus_pages(struct hstate *h, long delta)
 	 * After retaking hugetlb_lock, we need to recalculate 'needed'
 	 * because either resv_huge_pages or free_huge_pages may have changed.
 	 */
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 	needed = (h->resv_huge_pages + delta) -
 			(h->free_huge_pages + allocated);
 	if (needed > 0) {
@@ -2061,12 +2018,12 @@ static int gather_surplus_pages(struct hstate *h, long delta)
 		enqueue_huge_page(h, page);
 	}
 free:
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 
 	/* Free unnecessary surplus pages to the buddy allocator */
 	list_for_each_entry_safe(page, tmp, &surplus_list, lru)
 		put_page(page);
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 
 	return ret;
 }
@@ -2117,9 +2074,9 @@ static void return_unused_surplus_pages(struct hstate *h,
 	}
 
 out:
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 	update_and_free_pages_bulk(h, &page_list);
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 }
 
 
@@ -2464,7 +2421,7 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
 	if (ret)
 		goto out_uncharge_cgroup_reservation;
 
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 	/*
 	 * glb_chg is passed to indicate whether or not a page must be taken
 	 * from the global free pool (global change).  gbl_chg == 0 indicates
@@ -2472,7 +2429,7 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
 	 */
 	page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve, gbl_chg);
 	if (!page) {
-		spin_unlock(&hugetlb_lock);
+		spin_unlock_irq(&hugetlb_lock);
 		page = alloc_buddy_huge_page_with_mpol(h, vma, addr);
 		if (!page)
 			goto out_uncharge_cgroup;
@@ -2480,7 +2437,7 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
 			SetHPageRestoreReserve(page);
 			h->resv_huge_pages--;
 		}
-		spin_lock(&hugetlb_lock);
+		spin_lock_irq(&hugetlb_lock);
 		list_add(&page->lru, &h->hugepage_activelist);
 		/* Fall through */
 	}
@@ -2493,7 +2450,7 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
 						  h_cg, page);
 	}
 
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 
 	hugetlb_set_page_subpool(page, spool);
 
@@ -2706,9 +2663,9 @@ static void try_to_free_low(struct hstate *h, unsigned long count,
 	}
 
 out:
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 	update_and_free_pages_bulk(h, &page_list);
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 }
 #else
 static inline void try_to_free_low(struct hstate *h, unsigned long count,
@@ -2804,7 +2761,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 	 */
 	if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) {
 		if (count > persistent_huge_pages(h)) {
-			spin_unlock(&hugetlb_lock);
+			spin_unlock_irq(&hugetlb_lock);
 			mutex_unlock(&h->resize_lock);
 			NODEMASK_FREE(node_alloc_noretry);
 			return -EINVAL;
@@ -2834,14 +2791,14 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 		 * page, free_huge_page will handle it by freeing the page
 		 * and reducing the surplus.
 		 */
-		spin_unlock(&hugetlb_lock);
+		spin_unlock_irq(&hugetlb_lock);
 
 		/* yield cpu to avoid soft lockup */
 		cond_resched();
 
 		ret = alloc_pool_huge_page(h, nodes_allowed,
 						node_alloc_noretry);
-		spin_lock(&hugetlb_lock);
+		spin_lock_irq(&hugetlb_lock);
 		if (!ret)
 			goto out;
 
@@ -2881,9 +2838,9 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 		list_add(&page->lru, &page_list);
 	}
 	/* free the pages after dropping lock */
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 	update_and_free_pages_bulk(h, &page_list);
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 
 	while (count < persistent_huge_pages(h)) {
 		if (!adjust_pool_surplus(h, nodes_allowed, 1))
@@ -2891,7 +2848,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 	}
 out:
 	h->max_huge_pages = persistent_huge_pages(h);
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 	mutex_unlock(&h->resize_lock);
 
 	NODEMASK_FREE(node_alloc_noretry);
@@ -3047,9 +3004,9 @@ static ssize_t nr_overcommit_hugepages_store(struct kobject *kobj,
 	if (err)
 		return err;
 
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 	h->nr_overcommit_huge_pages = input;
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 
 	return count;
 }
@@ -3636,9 +3593,9 @@ int hugetlb_overcommit_handler(struct ctl_table *table, int write,
 		goto out;
 
 	if (write) {
-		spin_lock(&hugetlb_lock);
+		spin_lock_irq(&hugetlb_lock);
 		h->nr_overcommit_huge_pages = tmp;
-		spin_unlock(&hugetlb_lock);
+		spin_unlock_irq(&hugetlb_lock);
 	}
 out:
 	return ret;
@@ -3734,7 +3691,7 @@ static int hugetlb_acct_memory(struct hstate *h, long delta)
 	if (!delta)
 		return 0;
 
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 	/*
 	 * When cpuset is configured, it breaks the strict hugetlb page
 	 * reservation as the accounting is done on a global variable. Such
@@ -3773,7 +3730,7 @@ static int hugetlb_acct_memory(struct hstate *h, long delta)
 		return_unused_surplus_pages(h, (unsigned long) -delta);
 
 out:
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 	return ret;
 }
 
@@ -5837,7 +5794,7 @@ bool isolate_huge_page(struct page *page, struct list_head *list)
 {
 	bool ret = true;
 
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 	if (!PageHeadHuge(page) ||
 	    !HPageMigratable(page) ||
 	    !get_page_unless_zero(page)) {
@@ -5847,16 +5804,16 @@ bool isolate_huge_page(struct page *page, struct list_head *list)
 	ClearHPageMigratable(page);
 	list_move_tail(&page->lru, list);
 unlock:
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 	return ret;
 }
 
 void putback_active_hugepage(struct page *page)
 {
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 	SetHPageMigratable(page);
 	list_move_tail(&page->lru, &(page_hstate(page))->hugepage_activelist);
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 	put_page(page);
 }
 
@@ -5890,12 +5847,12 @@ void move_hugetlb_state(struct page *oldpage, struct page *newpage, int reason)
 		 */
 		if (new_nid == old_nid)
 			return;
-		spin_lock(&hugetlb_lock);
+		spin_lock_irq(&hugetlb_lock);
 		if (h->surplus_huge_pages_node[old_nid]) {
 			h->surplus_huge_pages_node[old_nid]--;
 			h->surplus_huge_pages_node[new_nid]++;
 		}
-		spin_unlock(&hugetlb_lock);
+		spin_unlock_irq(&hugetlb_lock);
 	}
 }
 
diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index 726b85f4f303..5383023d0cca 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -204,11 +204,11 @@ static void hugetlb_cgroup_css_offline(struct cgroup_subsys_state *css)
 	do {
 		idx = 0;
 		for_each_hstate(h) {
-			spin_lock(&hugetlb_lock);
+			spin_lock_irq(&hugetlb_lock);
 			list_for_each_entry(page, &h->hugepage_activelist, lru)
 				hugetlb_cgroup_move_parent(idx, h_cg, page);
 
-			spin_unlock(&hugetlb_lock);
+			spin_unlock_irq(&hugetlb_lock);
 			idx++;
 		}
 		cond_resched();
@@ -784,7 +784,7 @@ void hugetlb_cgroup_migrate(struct page *oldhpage, struct page *newhpage)
 	if (hugetlb_cgroup_disabled())
 		return;
 
-	spin_lock(&hugetlb_lock);
+	spin_lock_irq(&hugetlb_lock);
 	h_cg = hugetlb_cgroup_from_page(oldhpage);
 	h_cg_rsvd = hugetlb_cgroup_from_page_rsvd(oldhpage);
 	set_hugetlb_cgroup(oldhpage, NULL);
@@ -794,7 +794,7 @@ void hugetlb_cgroup_migrate(struct page *oldhpage, struct page *newhpage)
 	set_hugetlb_cgroup(newhpage, h_cg);
 	set_hugetlb_cgroup_rsvd(newhpage, h_cg_rsvd);
 	list_move(&newhpage->lru, &h->hugepage_activelist);
-	spin_unlock(&hugetlb_lock);
+	spin_unlock_irq(&hugetlb_lock);
 	return;
 }
 
-- 
2.30.2