linux-kernel - [PATCH v4 4/6] mm: hugetlb: retry dissolve page when hitting race

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20210113052209.75531-5-songmuchun@bytedance.com>
Date:   Wed, 13 Jan 2021 13:22:07 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     mike.kravetz@...cle.com, akpm@...ux-foundation.org
Cc:     n-horiguchi@...jp.nec.com, ak@...ux.intel.com, mhocko@...e.cz,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: [PATCH v4 4/6] mm: hugetlb: retry dissolve page when hitting race

There is a race between dissolve_free_huge_page() and put_page().
Theoretically, we should return -EBUSY when we encounter this race.
In fact, we have a chance to successfully dissolve the page if we
do a retry. Because the race window is quite small. If we seize
this opportunity, it is an optimization for increasing the success
rate of dissolving page.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 mm/hugetlb.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 4a9011e12175..898e4ea43e13 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1772,6 +1772,7 @@ int dissolve_free_huge_page(struct page *page)
 {
 	int rc = -EBUSY;
 
+retry:
 	/* Not to disrupt normal path by vainly holding hugetlb_lock */
 	if (!PageHuge(page))
 		return 0;
@@ -1793,8 +1794,23 @@ int dissolve_free_huge_page(struct page *page)
 		 * We should make sure that the page is already on the free list
 		 * when it is dissolved.
 		 */
-		if (unlikely(!PageHugeFreed(head)))
-			goto out;
+		if (unlikely(!PageHugeFreed(head))) {
+			spin_unlock(&hugetlb_lock);
+
+			/*
+			 * Theoretically, we should return -EBUSY when we
+			 * encounter this race. In fact, we have a chance
+			 * to successfully dissolve the page if we do a
+			 * retry. Because the race window is quite small.
+			 * If we seize this opportunity, it is an optimization
+			 * for increasing the success rate of dissolving page.
+			 */
+			while (PageHeadHuge(head) && !PageHugeFreed(head)) {
+				cond_resched();
+				cpu_relax();
+			}
+			goto retry;
+		}
 
 		/*
 		 * Move PageHWPoison flag from head page to the raw error page,
-- 
2.11.0