Commit 79aa925b authored Nov 01, 2020 by Mike Kravetz Committed by Linus Torvalds Nov 02, 2020

hugetlb_cgroup: fix reservation accounting



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.

  WARNING: CPU: 7 PID: 6636 at mm/page_counter.c:57 page_counter_uncharge+0x4b/0x50
  Modules linked in: ...
  CPU: 7 PID: 6636 Comm: qemu-system-x86 Not tainted 5.9.0 #137
  Hardware name: Gigabyte Technology Co., Ltd. X570 AORUS PRO/X570 AORUS PRO, BIOS F21 07/31/2020
  RIP: 0010:page_counter_uncharge+0x4b/0x50
  ...
  Call Trace:
    hugetlb_cgroup_uncharge_file_region+0x4b/0x80
    region_del+0x1d3/0x300
    hugetlb_unreserve_pages+0x39/0xb0
    remove_inode_hugepages+0x1a8/0x3d0
    hugetlbfs_fallocate+0x3c4/0x5c0
    vfs_fallocate+0x146/0x290
    __x64_sys_fallocate+0x3e/0x70
    do_syscall_64+0x33/0x40
    entry_SYSCALL_64_after_hwframe+0x44/0xa9

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

Fixes: 075a61d0 ("hugetlb_cgroup: add accounting for shared mappings")
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Cc: <stable@vger.kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Tejun Heo <tj@kernel.org>
Link: https://lkml.kernel.org/r/20201021204426.36069-1-mike.kravetz@oracle.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 46b1ee38

mm/hugetlb.c

+11 −9

Original line number	Diff line number	Diff line
		@@ -648,6 +648,8 @@ retry:
		}

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

		/* New entry for end of split region */
		nrg->from = t;
		@@ -660,9 +662,6 @@ retry:
		/* 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;
		@@ -678,17 +677,17 @@ retry:
		}

		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;
		}
		}

		@@ -2443,6 +2442,9 @@ 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;

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