Re: [PATCH 7/8] hugetlb: make free_huge_page irq safe
From: Michal Hocko
Date: Thu Mar 25 2021 - 07:22:18 EST
On Wed 24-03-21 17:28:34, Mike Kravetz wrote:
> 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, as seen in [1] this
> does not cover all cases. Instead, make the locks taken in the
> free_huge_page irq safe.
I would just call out the deadlock scenario here in the changelog
rathert than torture people by forcing them to follow up on the 0day
report. Something like the below?
"
"
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 patch does 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>
> ---
> mm/hugetlb.c | 169 +++++++++++++++++---------------------------
> mm/hugetlb_cgroup.c | 8 +--
> 2 files changed, 67 insertions(+), 110 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index a9785e73379f..e4c441b878f2 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;
> }
> @@ -1401,7 +1405,7 @@ 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
> @@ -1411,6 +1415,7 @@ 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);
> @@ -1439,7 +1444,7 @@ 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);
> @@ -1450,66 +1455,18 @@ 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);
> - }
> -}
> -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;
> + spin_unlock_irqrestore(&hugetlb_lock, flags);
> }
> -
> - __free_huge_page(page);
> }
>
> static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
> @@ -1519,11 +1476,11 @@ 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)
> @@ -1769,7 +1726,7 @@ 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;
> @@ -1786,7 +1743,7 @@ 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();
>
> /*
> @@ -1810,12 +1767,12 @@ 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;
> }
>
> @@ -1857,16 +1814,16 @@ 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
> @@ -1876,7 +1833,7 @@ 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 {
> @@ -1885,7 +1842,7 @@ 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;
> }
> @@ -1935,17 +1892,17 @@ 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);
> }
> @@ -1993,7 +1950,7 @@ 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);
> @@ -2010,7 +1967,7 @@ 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) {
> @@ -2050,12 +2007,12 @@ 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;
> }
> @@ -2107,13 +2064,13 @@ static void return_unused_surplus_pages(struct hstate *h,
> }
>
> out:
> - spin_unlock(&hugetlb_lock);
> + spin_unlock_irq(&hugetlb_lock);
> list_for_each_entry_safe(page, t_page, &page_list, lru) {
> list_del(&page->lru);
> update_and_free_page(h, page);
> cond_resched();
> }
> - spin_lock(&hugetlb_lock);
> + spin_lock_irq(&hugetlb_lock);
> }
>
>
> @@ -2348,7 +2305,7 @@ 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
> @@ -2356,7 +2313,7 @@ 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;
> @@ -2364,7 +2321,7 @@ 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 */
> }
> @@ -2377,7 +2334,7 @@ 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);
>
> @@ -2591,13 +2548,13 @@ static void try_to_free_low(struct hstate *h, unsigned long count,
> }
>
> out:
> - spin_unlock(&hugetlb_lock);
> + spin_unlock_irq(&hugetlb_lock);
> list_for_each_entry_safe(page, next, &page_list, lru) {
> list_del(&page->lru);
> update_and_free_page(h, page);
> cond_resched();
> }
> - spin_lock(&hugetlb_lock);
> + spin_lock_irq(&hugetlb_lock);
> }
> #else
> static inline void try_to_free_low(struct hstate *h, unsigned long count,
> @@ -2659,7 +2616,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
>
> /* mutex prevents concurrent adjustments for the same hstate */
> mutex_lock(&h->mutex);
> - spin_lock(&hugetlb_lock);
> + spin_lock_irq(&hugetlb_lock);
>
> /*
> * Check for a node specific request.
> @@ -2690,7 +2647,7 @@ 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->mutex);
> NODEMASK_FREE(node_alloc_noretry);
> return -EINVAL;
> @@ -2720,14 +2677,14 @@ 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;
>
> @@ -2768,13 +2725,13 @@ 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);
> list_for_each_entry_safe(page, t_page, &page_list, lru) {
> list_del(&page->lru);
> update_and_free_page(h, page);
> cond_resched();
> }
> - spin_lock(&hugetlb_lock);
> + spin_lock_irq(&hugetlb_lock);
>
> while (count < persistent_huge_pages(h)) {
> if (!adjust_pool_surplus(h, nodes_allowed, 1))
> @@ -2782,7 +2739,7 @@ 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->mutex);
>
> NODEMASK_FREE(node_alloc_noretry);
> @@ -2938,9 +2895,9 @@ 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;
> }
> @@ -3527,9 +3484,9 @@ 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;
> @@ -3625,7 +3582,7 @@ 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
> @@ -3664,7 +3621,7 @@ 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;
> }
>
> @@ -5727,7 +5684,7 @@ 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)) {
> @@ -5737,16 +5694,16 @@ 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);
> }
>
> @@ -5780,12 +5737,12 @@ 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
>
--
Michal Hocko
SUSE Labs