Re: [PATCH] hugetlb_cgroup: fix reservation accounting

[Michal Privoznik]

On 10/21/20 10:44 PM, 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>
> ---
>   mm/hugetlb.c | 20 +++++++++++---------
>   1 file changed, 11 insertions(+), 9 deletions(-)

I just tested this and can confirm it fixes the problem:

Tested-by: Michal Privoznik <mprivozn@xxxxxxxxxx>

Thank you!
Michal