mm/rmap: skip unfaulted VMAs on anon_vma clone, unlink

For both anon_vma_clone() and unlink_anon_vmas(), if the source VMA or the
VMA to be linked are unfaulted (e.g.  !vma->anon_vma), then the functions
do nothing.  Simply exit early in these cases.

In the unlink_anon_vmas() case we can also remove a conditional that
checks whether vma->anon_vma is set.

Link: https://lkml.kernel.org/r/085a25f7528e1c8c687276e9b856e88dc8f105ca.1768746221.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Chris Li <chriscli@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/rmap.c b/mm/rmap.c
index fe2fd9ab0deab631f6fcfa34218e11c3b875193b..3c5fb8fb105ffd02afb5ff215a94598bd8a3ec41 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -313,6 +313,9 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
 
        check_anon_vma_clone(dst, src);
 
+       if (!src->anon_vma)
+               return 0;
+
        list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
                struct anon_vma *anon_vma;
 
@@ -478,7 +481,10 @@ void unlink_anon_vmas(struct vm_area_struct *vma)
        mmap_assert_locked(vma->vm_mm);
 
        /* Unfaulted is a no-op. */
-       VM_WARN_ON_ONCE(!vma->anon_vma && !list_empty(&vma->anon_vma_chain));
+       if (!vma->anon_vma) {
+               VM_WARN_ON_ONCE(!list_empty(&vma->anon_vma_chain));
+               return;
+       }
 
        /*
         * Unlink each anon_vma chained to the VMA.  This list is ordered
@@ -502,15 +508,13 @@ void unlink_anon_vmas(struct vm_area_struct *vma)
                list_del(&avc->same_vma);
                anon_vma_chain_free(avc);
        }
-       if (vma->anon_vma) {
-               vma->anon_vma->num_active_vmas--;
 
-               /*
-                * vma would still be needed after unlink, and anon_vma will be prepared
-                * when handle fault.
-                */
-               vma->anon_vma = NULL;
-       }
+       vma->anon_vma->num_active_vmas--;
+       /*
+        * vma would still be needed after unlink, and anon_vma will be prepared
+        * when handle fault.
+        */
+       vma->anon_vma = NULL;
        unlock_anon_vma_root(root);
 
        /*