On 4/2/21 5:47 AM, Muchun Song wrote:
> On Wed, Mar 31, 2021 at 11:42 AM Mike Kravetz <mike.kravetz@xxxxxxxxxx> 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, 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>
>
> Hi Mike,
>
> Today I pulled the newest code (next-20210401). I found that
> alloc_and_dissolve_huge_page is not updated. In this function,
> hugetlb_lock is still non-irq safe. Maybe you or Oscar need
> to fix.
>
> Thanks.
Thank you Muchun,
Oscar's changes were not in Andrew's tree when I started on this series
and I failed to notice their inclusion. In addition,
isolate_or_dissolve_huge_page also needs updating as well as a change in
set_max_huge_pages that was omitted while rebasing.
Andrew, the following patch addresses those missing changes. Ideally,
the changes should be combined/included in this patch. If you want me
to sent another version of this patch or another series, let me know.
>From 450593eb3cea895f499ddc343c22424c552ea502 Mon Sep 17 00:00:00 2001
From: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Date: Fri, 2 Apr 2021 13:18:13 -0700
Subject: [PATCH] hugetlb: fix irq locking omissions
The pach "hugetlb: make free_huge_page irq safe" changed spin_*lock
calls to spin_*lock_irq* calls. However, it missed several places
in the file hugetlb.c. Add the overlooked changes.
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
mm/hugetlb.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index c22111f3da20..a6bfc6bcbc81 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2284,7 +2284,7 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
*/
page_ref_dec(new_page);
retry:
- spin_lock(&hugetlb_lock);
+ spin_lock_irq(&hugetlb_lock);
if (!PageHuge(old_page)) {
/*
* Freed from under us. Drop new_page too.
@@ -2297,7 +2297,7 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
* Fail with -EBUSY if not possible.
*/
update_and_free_page(h, new_page);
- spin_unlock(&hugetlb_lock);
+ spin_unlock_irq(&hugetlb_lock);
if (!isolate_huge_page(old_page, list))
ret = -EBUSY;
return ret;
@@ -2307,7 +2307,7 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
* freelist yet. Race window is small, so we can succed here if
* we retry.
*/
- spin_unlock(&hugetlb_lock);
+ spin_unlock_irq(&hugetlb_lock);
cond_resched();
goto retry;
} else {
@@ -2323,7 +2323,7 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
__enqueue_huge_page(&h->hugepage_freelists[nid], new_page);
}
unlock:
- spin_unlock(&hugetlb_lock);
+ spin_unlock_irq(&hugetlb_lock);
return ret;
}
@@ -2339,15 +2339,15 @@ int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list)
* to carefully check the state under the lock.
* Return success when racing as if we dissolved the page ourselves.
*/
- spin_lock(&hugetlb_lock);
+ spin_lock_irq(&hugetlb_lock);
if (PageHuge(page)) {
head = compound_head(page);
h = page_hstate(head);
} else {
- spin_unlock(&hugetlb_lock);
+ spin_unlock_irq(&hugetlb_lock);
return 0;
}
- spin_unlock(&hugetlb_lock);
+ spin_unlock_irq(&hugetlb_lock);
/*
* Fence off gigantic pages as there is a cyclic dependency between
@@ -2737,7 +2737,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
* pages in hstate via the proc/sysfs interfaces.
*/
mutex_lock(&h->resize_lock);
- spin_lock(&hugetlb_lock);
+ spin_lock_irq(&hugetlb_lock);
/*
* Check for a node specific request.
--
2.30.2
