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mm: fix some minor per-VMA lock issues in userfaultfd

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Rename lock_vma() to uffd_lock_vma() because it really is uffd specific. 
Remove comment referencing unlock_vma() which doesn't exist.  Fix the
comment about lock_vma_under_rcu() which I just made incorrect.

Link: https://lkml.kernel.org/r/20240426144506.1290619-4-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2024-04-26 15:45:02 +01:00 committed by Andrew Morton
parent a373baed5a
commit 73b4a0cd82
1 changed files with 9 additions and 11 deletions
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20
mm/userfaultfd.c
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@ -56,17 +56,16 @@ struct vm_area_struct *find_vma_and_prepare_anon(struct mm_struct *mm,
#ifdef CONFIG_PER_VMA_LOCK #ifdef CONFIG_PER_VMA_LOCK
/* /*
* lock_vma() - Lookup and lock vma corresponding to @address. * uffd_lock_vma() - Lookup and lock vma corresponding to @address.
* @mm: mm to search vma in. * @mm: mm to search vma in.
* @address: address that the vma should contain. * @address: address that the vma should contain.
* *
* Should be called without holding mmap_lock. vma should be unlocked after use * Should be called without holding mmap_lock.
* with unlock_vma().
* *
* Return: A locked vma containing @address, -ENOENT if no vma is found, or * Return: A locked vma containing @address, -ENOENT if no vma is found, or
* -ENOMEM if anon_vma couldn't be allocated. * -ENOMEM if anon_vma couldn't be allocated.
*/ */
static struct vm_area_struct *lock_vma(struct mm_struct *mm, static struct vm_area_struct *uffd_lock_vma(struct mm_struct *mm,
unsigned long address) unsigned long address)
{ {
struct vm_area_struct *vma; struct vm_area_struct *vma;
@ -74,9 +73,8 @@ static struct vm_area_struct *lock_vma(struct mm_struct *mm,
vma = lock_vma_under_rcu(mm, address); vma = lock_vma_under_rcu(mm, address);
if (vma) { if (vma) {
/* /*
* lock_vma_under_rcu() only checks anon_vma for private * We know we're going to need to use anon_vma, so check
* anonymous mappings. But we need to ensure it is assigned in * that early.
* private file-backed vmas as well.
*/ */
if (!(vma->vm_flags & VM_SHARED) && unlikely(!vma->anon_vma)) if (!(vma->vm_flags & VM_SHARED) && unlikely(!vma->anon_vma))
vma_end_read(vma); vma_end_read(vma);
@ -107,7 +105,7 @@ static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm,
{ {
struct vm_area_struct *dst_vma; struct vm_area_struct *dst_vma;
dst_vma = lock_vma(dst_mm, dst_start); dst_vma = uffd_lock_vma(dst_mm, dst_start);
if (IS_ERR(dst_vma) || validate_dst_vma(dst_vma, dst_start + len)) if (IS_ERR(dst_vma) || validate_dst_vma(dst_vma, dst_start + len))
return dst_vma; return dst_vma;
@ -1401,7 +1399,7 @@ static int uffd_move_lock(struct mm_struct *mm,
struct vm_area_struct *vma; struct vm_area_struct *vma;
int err; int err;
vma = lock_vma(mm, dst_start); vma = uffd_lock_vma(mm, dst_start);
if (IS_ERR(vma)) if (IS_ERR(vma))
return PTR_ERR(vma); return PTR_ERR(vma);
@ -1416,7 +1414,7 @@ static int uffd_move_lock(struct mm_struct *mm,
} }
/* /*
* Using lock_vma() to get src_vma can lead to following deadlock: * Using uffd_lock_vma() to get src_vma can lead to following deadlock:
* *
* Thread1 Thread2 * Thread1 Thread2
* ------- ------- * ------- -------
@ -1438,7 +1436,7 @@ static int uffd_move_lock(struct mm_struct *mm,
err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap); err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
if (!err) { if (!err) {
/* /*
* See comment in lock_vma() as to why not using * See comment in uffd_lock_vma() as to why not using
* vma_start_read() here. * vma_start_read() here.
*/ */
down_read(&(*dst_vmap)->vm_lock->lock); down_read(&(*dst_vmap)->vm_lock->lock);