On 2022/10/20 4:19, Mike Kravetz wrote: > The hugetlb vma_lock structure hangs off the vm_private_data pointer > of sharable hugetlb vmas. The structure is vma specific and can not > be shared between vmas. At fork and various other times, vmas are > duplicated via vm_area_dup(). When this happens, the pointer in the > newly created vma must be cleared and the structure reallocated. Two > hugetlb specific routines deal with this hugetlb_dup_vma_private and > hugetlb_vm_op_open. Both routines are called for newly created vmas. > hugetlb_dup_vma_private would always clear the pointer and > hugetlb_vm_op_open would allocate the new vms_lock structure. This did > not work in the case of this calling sequence pointed out in [1]. > move_vma > copy_vma > new_vma = vm_area_dup(vma); > new_vma->vm_ops->open(new_vma); --> new_vma has its own vma lock. > is_vm_hugetlb_page(vma) > clear_vma_resv_huge_pages > hugetlb_dup_vma_private --> vma->vm_private_data is set to NULL > When clearing hugetlb_dup_vma_private we actually leak the associated > vma_lock structure. > > The vma_lock structure contains a pointer to the associated vma. This > information can be used in hugetlb_dup_vma_private and hugetlb_vm_op_open > to ensure we only clear the vm_private_data of newly created (copied) > vmas. In such cases, the vma->vma_lock->vma field will not point to the > vma. > > Update hugetlb_dup_vma_private and hugetlb_vm_op_open to not clear > vm_private_data if vma->vma_lock->vma == vma. Also, log a warning if > hugetlb_vm_op_open ever encounters the case where vma_lock has already > been correctly allocated for the vma. > > [1] https://lore.kernel.org/linux-mm/5154292a-4c55-28cd-0935-82441e512fc3@xxxxxxxxxx/ > > Fixes: 131a79b474e9 ("hugetlb: fix vma lock handling during split vma and range unmapping") > Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Thanks for update. This patch looks good to me. Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> Thanks, Miaohe Lin > --- > v2 - Allocate vma_lock in hugetlb_vm_op_open if !vma->vm_private_data > on entry. Thanks Miaohe Lin! > > mm/hugetlb.c | 35 +++++++++++++++++++++++++++-------- > 1 file changed, 27 insertions(+), 8 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 02f781624fce..ccdffc2fa1ca 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -1014,15 +1014,23 @@ void hugetlb_dup_vma_private(struct vm_area_struct *vma) > VM_BUG_ON_VMA(!is_vm_hugetlb_page(vma), vma); > /* > * Clear vm_private_data > + * - For shared mappings this is a per-vma semaphore that may be > + * allocated in a subsequent call to hugetlb_vm_op_open. > + * Before clearing, make sure pointer is not associated with vma > + * as this will leak the structure. This is the case when called > + * via clear_vma_resv_huge_pages() and hugetlb_vm_op_open has already > + * been called to allocate a new structure. > * - For MAP_PRIVATE mappings, this is the reserve map which does > * not apply to children. Faults generated by the children are > * not guaranteed to succeed, even if read-only. > - * - For shared mappings this is a per-vma semaphore that may be > - * allocated in a subsequent call to hugetlb_vm_op_open. > */ > - vma->vm_private_data = (void *)0; > - if (!(vma->vm_flags & VM_MAYSHARE)) > - return; > + if (vma->vm_flags & VM_MAYSHARE) { > + struct hugetlb_vma_lock *vma_lock = vma->vm_private_data; > + > + if (vma_lock && vma_lock->vma != vma) > + vma->vm_private_data = NULL; > + } else > + vma->vm_private_data = NULL; > } > > /* > @@ -4601,6 +4609,7 @@ static void hugetlb_vm_op_open(struct vm_area_struct *vma) > struct resv_map *resv = vma_resv_map(vma); > > /* > + * HPAGE_RESV_OWNER indicates a private mapping. > * This new VMA should share its siblings reservation map if present. > * The VMA will only ever have a valid reservation map pointer where > * it is being copied for another still existing VMA. As that VMA > @@ -4615,11 +4624,21 @@ static void hugetlb_vm_op_open(struct vm_area_struct *vma) > > /* > * vma_lock structure for sharable mappings is vma specific. > - * Clear old pointer (if copied via vm_area_dup) and create new. > + * Clear old pointer (if copied via vm_area_dup) and allocate > + * new structure. Before clearing, make sure vma_lock is not > + * for this vma. > */ > if (vma->vm_flags & VM_MAYSHARE) { > - vma->vm_private_data = NULL; > - hugetlb_vma_lock_alloc(vma); > + struct hugetlb_vma_lock *vma_lock = vma->vm_private_data; > + > + if (vma_lock) { > + if (vma_lock->vma != vma) { > + vma->vm_private_data = NULL; > + hugetlb_vma_lock_alloc(vma); > + } else > + pr_warn("HugeTLB: vma_lock already exists in %s.\n", __func__); > + } else > + hugetlb_vma_lock_alloc(vma); > } > } > >
