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>
---
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);
}
}
--
2.37.3
