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Subject[PATCH] hugetlb_cgroup: fix reservation accounting
Date
Michal Privoznik was using "free page reporting" in QEMU/virtio-balloon
with hugetlbfs and hit the warning below. QEMU with free page hinting
uses fallocate(FALLOC_FL_PUNCH_HOLE) to discard pages that are reported
as free by a VM. The reporting granularity is in pageblock granularity.
So when the guest reports 2M chunks, we fallocate(FALLOC_FL_PUNCH_HOLE)
one huge page in QEMU.

[ 315.251417] ------------[ cut here ]------------
[ 315.251424] WARNING: CPU: 7 PID: 6636 at mm/page_counter.c:57 page_counter_uncharge+0x4b/0x50
[ 315.251425] Modules linked in: ...
[ 315.251466] CPU: 7 PID: 6636 Comm: qemu-system-x86 Not tainted 5.9.0 #137
[ 315.251467] Hardware name: Gigabyte Technology Co., Ltd. X570 AORUS PRO/X570 AORUS PRO, BIOS F21 07/31/2020
[ 315.251469] RIP: 0010:page_counter_uncharge+0x4b/0x50
...
[ 315.251479] Call Trace:
[ 315.251485] hugetlb_cgroup_uncharge_file_region+0x4b/0x80
[ 315.251487] region_del+0x1d3/0x300
[ 315.251489] hugetlb_unreserve_pages+0x39/0xb0
[ 315.251492] remove_inode_hugepages+0x1a8/0x3d0
[ 315.251495] ? tlb_finish_mmu+0x7a/0x1d0
[ 315.251497] hugetlbfs_fallocate+0x3c4/0x5c0
[ 315.251519] ? kvm_arch_vcpu_ioctl_run+0x614/0x1700 [kvm]
[ 315.251522] ? file_has_perm+0xa2/0xb0
[ 315.251524] ? inode_security+0xc/0x60
[ 315.251525] ? selinux_file_permission+0x4e/0x120
[ 315.251527] vfs_fallocate+0x146/0x290
[ 315.251529] __x64_sys_fallocate+0x3e/0x70
[ 315.251531] do_syscall_64+0x33/0x40
[ 315.251533] entry_SYSCALL_64_after_hwframe+0x44/0xa9
...
[ 315.251542] ---[ end trace 4c88c62ccb1349c9 ]---

Investigation of the issue uncovered bugs in hugetlb cgroup reservation
accounting. This patch addresses the found issues.

Fixes: 075a61d07a8e ("hugetlb_cgroup: add accounting for shared mappings")
Cc: <stable@vger.kernel.org>
Reported-by: Michal Privoznik <mprivozn@redhat.com>
Co-developed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
---
mm/hugetlb.c | 20 +++++++++++---------
1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 67fc6383995b..b853a11de14f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -655,6 +655,8 @@ static long region_del(struct resv_map *resv, long f, long t)
}

del += t - f;
+ hugetlb_cgroup_uncharge_file_region(
+ resv, rg, t - f);

/* New entry for end of split region */
nrg->from = t;
@@ -667,9 +669,6 @@ static long region_del(struct resv_map *resv, long f, long t)
/* Original entry is trimmed */
rg->to = f;

- hugetlb_cgroup_uncharge_file_region(
- resv, rg, nrg->to - nrg->from);
-
list_add(&nrg->link, &rg->link);
nrg = NULL;
break;
@@ -685,17 +684,17 @@ 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 +2453,9 @@ 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
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