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;