linux-kernel - Re: cgroup and FALLOC_FL_PUNCH_HOLE: WARNING: CPU: 13 PID: 2438 at mm/page_counter.c:57 page_counter

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Date:   Tue, 20 Oct 2020 20:35:03 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     David Hildenbrand <david@...hat.com>,
        Mina Almasry <almasrymina@...gle.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Michal Privoznik <mprivozn@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Muchun Song <songmuchun@...edance.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Tejun Heo <tj@...nel.org>
Subject: Re: cgroup and FALLOC_FL_PUNCH_HOLE: WARNING: CPU: 13 PID: 2438 at
 mm/page_counter.c:57 page_counter_uncharge+0x4b/0x5

On 10/20/20 6:38 AM, David Hildenbrand wrote:
> 
> I'm bisecting the warning right now. Looks like it was introduced in v5.7.

I found the following bugs in the cgroup reservation accounting.  The ones
in region_del are pretty obvious as the number of pages to uncharge would
always be zero.  The one on alloc_huge_page needs racing code to expose.

With these fixes, my testing is showing consistent/correct results for
hugetlb reservation cgroup accounting.

It would be good if Mina (at least) would look these over.  Would also
be interesting to know if these fixes address the bug seen with the qemu
use case.

I'm still doing more testing and code inspection to look for other issues.

>From 861bcd7d0443f18a5fed3c3ddc5f1c71e78c4ef4 Mon Sep 17 00:00:00 2001
From: Mike Kravetz <mike.kravetz@...cle.com>
Date: Tue, 20 Oct 2020 20:21:42 -0700
Subject: [PATCH] hugetlb_cgroup: fix reservation accounting

Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
---
 mm/hugetlb.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 67fc6383995b..c92366313780 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -685,17 +685,17 @@ static long region_del(struct resv_map *resv, long f, long t)
 		}
 
 		if (f <= rg->from) {	/* Trim beginning of region */
-			del += t - rg->from;
-			rg->from = t;
-
 			hugetlb_cgroup_uncharge_file_region(resv, rg,
 							    t - rg->from);
-		} else {		/* Trim end of region */
-			del += rg->to - f;
-			rg->to = f;
 
+			del += t - rg->from;
+			rg->from = t;
+		} else {		/* Trim end of region */
 			hugetlb_cgroup_uncharge_file_region(resv, rg,
 							    rg->to - f);
+
+			del += rg->to - f;
+			rg->to = f;
 		}
 	}
 
@@ -2454,6 +2454,9 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
 
 		rsv_adjust = hugepage_subpool_put_pages(spool, 1);
 		hugetlb_acct_memory(h, -rsv_adjust);
+		if (deferred_reserve)
+			hugetlb_cgroup_uncharge_page_rsvd(hstate_index(h),
+					pages_per_huge_page(h), page);
 	}
 	return page;
 
-- 
2.25.4