On Wed, Oct 21, 2020 at 01:44:26PM -0700, Mike Kravetz wrote:
> 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@xxxxxxxxxxxxxxx>
> Reported-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
> Co-developed-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> 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
