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

From: Mike Kravetz
Date: Wed Mar 24 2021 - 20:30:43 EST

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.

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>
---
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