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Subject[PATCH v2] hugetlbfs: Disable softIRQ when taking hugetlb_lock
Date
The following lockdep splat was observed when a certain hugetlbfs test
was run:

[ 612.388273] ================================
[ 612.411273] WARNING: inconsistent lock state
[ 612.432273] 4.18.0-159.el8.x86_64+debug #1 Tainted: G W --------- - -
[ 612.469273] --------------------------------
[ 612.489273] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
[ 612.517273] swapper/30/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
[ 612.541273] ffffffff9acdc038 (hugetlb_lock){+.?.}, at: free_huge_page+0x36f/0xaa0
[ 612.576273] {SOFTIRQ-ON-W} state was registered at:
[ 612.598273] lock_acquire+0x14f/0x3b0
[ 612.616273] _raw_spin_lock+0x30/0x70
[ 612.634273] __nr_hugepages_store_common+0x11b/0xb30
[ 612.657273] hugetlb_sysctl_handler_common+0x209/0x2d0
[ 612.681273] proc_sys_call_handler+0x37f/0x450
[ 612.703273] vfs_write+0x157/0x460
[ 612.719273] ksys_write+0xb8/0x170
[ 612.736273] do_syscall_64+0xa5/0x4d0
[ 612.753273] entry_SYSCALL_64_after_hwframe+0x6a/0xdf
[ 612.777273] irq event stamp: 691296
[ 612.794273] hardirqs last enabled at (691296): [<ffffffff99bb034b>] _raw_spin_unlock_irqrestore+0x4b/0x60
[ 612.839273] hardirqs last disabled at (691295): [<ffffffff99bb0ad2>] _raw_spin_lock_irqsave+0x22/0x81
[ 612.882273] softirqs last enabled at (691284): [<ffffffff97ff0c63>] irq_enter+0xc3/0xe0
[ 612.922273] softirqs last disabled at (691285): [<ffffffff97ff0ebe>] irq_exit+0x23e/0x2b0
[ 612.962273]
[ 612.962273] other info that might help us debug this:
[ 612.993273] Possible unsafe locking scenario:
[ 612.993273]
[ 613.020273] CPU0
[ 613.031273] ----
[ 613.042273] lock(hugetlb_lock);
[ 613.057273] <Interrupt>
[ 613.069273] lock(hugetlb_lock);
[ 613.085273]
[ 613.085273] *** DEADLOCK ***
:
[ 613.245273] Call Trace:
[ 613.256273] <IRQ>
[ 613.265273] dump_stack+0x9a/0xf0
[ 613.281273] mark_lock+0xd0c/0x12f0
[ 613.297273] ? print_shortest_lock_dependencies+0x80/0x80
[ 613.322273] ? sched_clock_cpu+0x18/0x1e0
[ 613.341273] __lock_acquire+0x146b/0x48c0
[ 613.360273] ? trace_hardirqs_on+0x10/0x10
[ 613.379273] ? trace_hardirqs_on_caller+0x27b/0x580
[ 613.401273] lock_acquire+0x14f/0x3b0
[ 613.419273] ? free_huge_page+0x36f/0xaa0
[ 613.440273] _raw_spin_lock+0x30/0x70
[ 613.458273] ? free_huge_page+0x36f/0xaa0
[ 613.477273] free_huge_page+0x36f/0xaa0
[ 613.495273] bio_check_pages_dirty+0x2fc/0x5c0
[ 613.516273] clone_endio+0x17f/0x670 [dm_mod]
[ 613.536273] ? disable_discard+0x90/0x90 [dm_mod]
[ 613.558273] ? bio_endio+0x4ba/0x930
[ 613.575273] ? blk_account_io_completion+0x400/0x530
[ 613.598273] blk_update_request+0x276/0xe50
[ 613.617273] scsi_end_request+0x7b/0x6a0
[ 613.636273] ? lock_downgrade+0x6f0/0x6f0
[ 613.654273] scsi_io_completion+0x1c6/0x1570
[ 613.674273] ? sd_completed_bytes+0x3a0/0x3a0 [sd_mod]
[ 613.698273] ? scsi_mq_requeue_cmd+0xc0/0xc0
[ 613.718273] blk_done_softirq+0x22e/0x350
[ 613.737273] ? blk_softirq_cpu_dead+0x230/0x230
[ 613.758273] __do_softirq+0x23d/0xad8
[ 613.776273] irq_exit+0x23e/0x2b0
[ 613.792273] do_IRQ+0x11a/0x200
[ 613.806273] common_interrupt+0xf/0xf
[ 613.823273] </IRQ>

Since hugetlb_lock can be taken from both process and softIRQ contexts,
we need to protect the lock from nested locking by disabling softIRQ
using spin_lock_bh() before taking it.

Currently, only free_huge_page() is known to be called from softIRQ
context.

Signed-off-by: Waiman Long <longman@redhat.com>
---
mm/hugetlb.c | 100 ++++++++++++++++++++++++++++-----------------------
1 file changed, 55 insertions(+), 45 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ac65bb5e38ac..5426f59683d9 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -59,7 +59,9 @@ static bool __initdata parsed_valid_hugepagesz = true;

/*
* Protects updates to hugepage_freelists, hugepage_activelist, nr_huge_pages,
- * free_huge_pages, and surplus_huge_pages.
+ * free_huge_pages, and surplus_huge_pages. These protected data can be
+ * accessed from both process and softIRQ contexts. Therefore, the spinlock
+ * needs to be acquired with softIRQ disabled to prevent nested locking.
*/
DEFINE_SPINLOCK(hugetlb_lock);

@@ -1175,7 +1177,7 @@ void free_huge_page(struct page *page)
restore_reserve = true;
}

- spin_lock(&hugetlb_lock);
+ spin_lock_bh(&hugetlb_lock);
clear_page_huge_active(page);
hugetlb_cgroup_uncharge_page(hstate_index(h),
pages_per_huge_page(h), page);
@@ -1196,18 +1198,18 @@ void free_huge_page(struct page *page)
arch_clear_hugepage_flags(page);
enqueue_huge_page(h, page);
}
- spin_unlock(&hugetlb_lock);
+ spin_unlock_bh(&hugetlb_lock);
}

static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
{
INIT_LIST_HEAD(&page->lru);
set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
- spin_lock(&hugetlb_lock);
+ spin_lock_bh(&hugetlb_lock);
set_hugetlb_cgroup(page, NULL);
h->nr_huge_pages++;
h->nr_huge_pages_node[nid]++;
- spin_unlock(&hugetlb_lock);
+ spin_unlock_bh(&hugetlb_lock);
}

static void prep_compound_gigantic_page(struct page *page, unsigned int order)
@@ -1438,7 +1440,7 @@ int dissolve_free_huge_page(struct page *page)
if (!PageHuge(page))
return 0;

- spin_lock(&hugetlb_lock);
+ spin_lock_bh(&hugetlb_lock);
if (!PageHuge(page)) {
rc = 0;
goto out;
@@ -1466,7 +1468,7 @@ int dissolve_free_huge_page(struct page *page)
rc = 0;
}
out:
- spin_unlock(&hugetlb_lock);
+ spin_unlock_bh(&hugetlb_lock);
return rc;
}

@@ -1508,16 +1510,16 @@ 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_bh(&hugetlb_lock);
if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages)
goto out_unlock;
- spin_unlock(&hugetlb_lock);
+ spin_unlock_bh(&hugetlb_lock);

page = alloc_fresh_huge_page(h, gfp_mask, nid, nmask, NULL);
if (!page)
return NULL;

- spin_lock(&hugetlb_lock);
+ spin_lock_bh(&hugetlb_lock);
/*
* We could have raced with the pool size change.
* Double check that and simply deallocate the new page
@@ -1527,7 +1529,7 @@ static struct page *alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask,
*/
if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages) {
SetPageHugeTemporary(page);
- spin_unlock(&hugetlb_lock);
+ spin_unlock_bh(&hugetlb_lock);
put_page(page);
return NULL;
} else {
@@ -1536,7 +1538,7 @@ static struct page *alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask,
}

out_unlock:
- spin_unlock(&hugetlb_lock);
+ spin_unlock_bh(&hugetlb_lock);

return page;
}
@@ -1591,10 +1593,10 @@ struct page *alloc_huge_page_node(struct hstate *h, int nid)
if (nid != NUMA_NO_NODE)
gfp_mask |= __GFP_THISNODE;

- spin_lock(&hugetlb_lock);
+ spin_lock_bh(&hugetlb_lock);
if (h->free_huge_pages - h->resv_huge_pages > 0)
page = dequeue_huge_page_nodemask(h, gfp_mask, nid, NULL);
- spin_unlock(&hugetlb_lock);
+ spin_unlock_bh(&hugetlb_lock);

if (!page)
page = alloc_migrate_huge_page(h, gfp_mask, nid, NULL);
@@ -1608,17 +1610,17 @@ struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
{
gfp_t gfp_mask = htlb_alloc_mask(h);

- spin_lock(&hugetlb_lock);
+ spin_lock_bh(&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_bh(&hugetlb_lock);
return page;
}
}
- spin_unlock(&hugetlb_lock);
+ spin_unlock_bh(&hugetlb_lock);

return alloc_migrate_huge_page(h, gfp_mask, preferred_nid, nmask);
}
@@ -1664,7 +1666,7 @@ static int gather_surplus_pages(struct hstate *h, int delta)

ret = -ENOMEM;
retry:
- spin_unlock(&hugetlb_lock);
+ spin_unlock_bh(&hugetlb_lock);
for (i = 0; i < needed; i++) {
page = alloc_surplus_huge_page(h, htlb_alloc_mask(h),
NUMA_NO_NODE, NULL);
@@ -1681,7 +1683,7 @@ static int gather_surplus_pages(struct hstate *h, int 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_bh(&hugetlb_lock);
needed = (h->resv_huge_pages + delta) -
(h->free_huge_pages + allocated);
if (needed > 0) {
@@ -1719,12 +1721,12 @@ static int gather_surplus_pages(struct hstate *h, int delta)
enqueue_huge_page(h, page);
}
free:
- spin_unlock(&hugetlb_lock);
+ spin_unlock_bh(&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_bh(&hugetlb_lock);

return ret;
}
@@ -1738,7 +1740,7 @@ static int gather_surplus_pages(struct hstate *h, int delta)
* the reservation. As many as unused_resv_pages may be freed.
*
* Called with hugetlb_lock held. However, the lock could be dropped (and
- * reacquired) during calls to cond_resched_lock. Whenever dropping the lock,
+ * reacquired) around calls to cond_resched(). Whenever dropping the lock,
* we must make sure nobody else can claim pages we are in the process of
* freeing. Do this by ensuring resv_huge_page always is greater than the
* number of huge pages we plan to free when dropping the lock.
@@ -1775,7 +1777,11 @@ static void return_unused_surplus_pages(struct hstate *h,
unused_resv_pages--;
if (!free_pool_huge_page(h, &node_states[N_MEMORY], 1))
goto out;
- cond_resched_lock(&hugetlb_lock);
+ if (need_resched()) {
+ spin_unlock_bh(&hugetlb_lock);
+ cond_resched();
+ spin_lock_bh(&hugetlb_lock);
+ }
}

out:
@@ -1994,7 +2000,7 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
if (ret)
goto out_subpool_put;

- spin_lock(&hugetlb_lock);
+ spin_lock_bh(&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
@@ -2002,7 +2008,7 @@ 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_bh(&hugetlb_lock);
page = alloc_buddy_huge_page_with_mpol(h, vma, addr);
if (!page)
goto out_uncharge_cgroup;
@@ -2010,12 +2016,12 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
SetPagePrivate(page);
h->resv_huge_pages--;
}
- spin_lock(&hugetlb_lock);
+ spin_lock_bh(&hugetlb_lock);
list_move(&page->lru, &h->hugepage_activelist);
/* Fall through */
}
hugetlb_cgroup_commit_charge(idx, pages_per_huge_page(h), h_cg, page);
- spin_unlock(&hugetlb_lock);
+ spin_unlock_bh(&hugetlb_lock);

set_page_private(page, (unsigned long)spool);

@@ -2269,7 +2275,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
else
return -ENOMEM;

- spin_lock(&hugetlb_lock);
+ spin_lock_bh(&hugetlb_lock);

/*
* Check for a node specific request.
@@ -2300,7 +2306,7 @@ 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_bh(&hugetlb_lock);
NODEMASK_FREE(node_alloc_noretry);
return -EINVAL;
}
@@ -2329,14 +2335,14 @@ 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_bh(&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_bh(&hugetlb_lock);
if (!ret)
goto out;

@@ -2366,7 +2372,11 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
while (min_count < persistent_huge_pages(h)) {
if (!free_pool_huge_page(h, nodes_allowed, 0))
break;
- cond_resched_lock(&hugetlb_lock);
+ if (need_resched()) {
+ spin_unlock_bh(&hugetlb_lock);
+ cond_resched();
+ spin_lock_bh(&hugetlb_lock);
+ }
}
while (count < persistent_huge_pages(h)) {
if (!adjust_pool_surplus(h, nodes_allowed, 1))
@@ -2374,7 +2384,7 @@ 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_bh(&hugetlb_lock);

NODEMASK_FREE(node_alloc_noretry);

@@ -2528,9 +2538,9 @@ static ssize_t nr_overcommit_hugepages_store(struct kobject *kobj,
if (err)
return err;

- spin_lock(&hugetlb_lock);
+ spin_lock_bh(&hugetlb_lock);
h->nr_overcommit_huge_pages = input;
- spin_unlock(&hugetlb_lock);
+ spin_unlock_bh(&hugetlb_lock);

return count;
}
@@ -2978,9 +2988,9 @@ int hugetlb_overcommit_handler(struct ctl_table *table, int write,
goto out;

if (write) {
- spin_lock(&hugetlb_lock);
+ spin_lock_bh(&hugetlb_lock);
h->nr_overcommit_huge_pages = tmp;
- spin_unlock(&hugetlb_lock);
+ spin_unlock_bh(&hugetlb_lock);
}
out:
return ret;
@@ -3071,7 +3081,7 @@ static int hugetlb_acct_memory(struct hstate *h, long delta)
{
int ret = -ENOMEM;

- spin_lock(&hugetlb_lock);
+ spin_lock_bh(&hugetlb_lock);
/*
* When cpuset is configured, it breaks the strict hugetlb page
* reservation as the accounting is done on a global variable. Such
@@ -3104,7 +3114,7 @@ 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_bh(&hugetlb_lock);
return ret;
}

@@ -4970,7 +4980,7 @@ bool isolate_huge_page(struct page *page, struct list_head *list)
bool ret = true;

VM_BUG_ON_PAGE(!PageHead(page), page);
- spin_lock(&hugetlb_lock);
+ spin_lock_bh(&hugetlb_lock);
if (!page_huge_active(page) || !get_page_unless_zero(page)) {
ret = false;
goto unlock;
@@ -4978,17 +4988,17 @@ bool isolate_huge_page(struct page *page, struct list_head *list)
clear_page_huge_active(page);
list_move_tail(&page->lru, list);
unlock:
- spin_unlock(&hugetlb_lock);
+ spin_unlock_bh(&hugetlb_lock);
return ret;
}

void putback_active_hugepage(struct page *page)
{
VM_BUG_ON_PAGE(!PageHead(page), page);
- spin_lock(&hugetlb_lock);
+ spin_lock_bh(&hugetlb_lock);
set_page_huge_active(page);
list_move_tail(&page->lru, &(page_hstate(page))->hugepage_activelist);
- spin_unlock(&hugetlb_lock);
+ spin_unlock_bh(&hugetlb_lock);
put_page(page);
}

@@ -5016,11 +5026,11 @@ void move_hugetlb_state(struct page *oldpage, struct page *newpage, int reason)
SetPageHugeTemporary(oldpage);
ClearPageHugeTemporary(newpage);

- spin_lock(&hugetlb_lock);
+ spin_lock_bh(&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_bh(&hugetlb_lock);
}
}
--
2.18.1
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