1 files changed, 158 insertions, 0 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index 5e0cc99e9cd5..e5f9cb83d6d4 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2268,3 +2268,161 @@ int install_special_mapping(struct mm_struct *mm,
 
         return 0;
 }
+
+static DEFINE_MUTEX(mm_all_locks_mutex);
+
+static void vm_lock_anon_vma(struct anon_vma *anon_vma)
+{
+        if (!test_bit(0, (unsigned long *) &anon_vma->head.next)) {
+                /*
+                 * The LSB of head.next can't change from under us
+                 * because we hold the mm_all_locks_mutex.
+                 */
+                spin_lock(&anon_vma->lock);
+                /*
+                 * We can safely modify head.next after taking the
+                 * anon_vma->lock. If some other vma in this mm shares
+                 * the same anon_vma we won't take it again.
+                 *
+                 * No need of atomic instructions here, head.next
+                 * can't change from under us thanks to the
+                 * anon_vma->lock.
+                 */
+                if (__test_and_set_bit(0, (unsigned long *)
+                                       &anon_vma->head.next))
+                        BUG();
+        }
+}
+
+static void vm_lock_mapping(struct address_space *mapping)
+{
+        if (!test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
+                /*
+                 * AS_MM_ALL_LOCKS can't change from under us because
+                 * we hold the mm_all_locks_mutex.
+                 *
+                 * Operations on ->flags have to be atomic because
+                 * even if AS_MM_ALL_LOCKS is stable thanks to the
+                 * mm_all_locks_mutex, there may be other cpus
+                 * changing other bitflags in parallel to us.
+                 */
+                if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
+                        BUG();
+                spin_lock(&mapping->i_mmap_lock);
+        }
+}
+
+/*
+ * This operation locks against the VM for all pte/vma/mm related
+ * operations that could ever happen on a certain mm. This includes
+ * vmtruncate, try_to_unmap, and all page faults.
+ *
+ * The caller must take the mmap_sem in write mode before calling
+ * mm_take_all_locks(). The caller isn't allowed to release the
+ * mmap_sem until mm_drop_all_locks() returns.
+ *
+ * mmap_sem in write mode is required in order to block all operations
+ * that could modify pagetables and free pages without need of
+ * altering the vma layout (for example populate_range() with
+ * nonlinear vmas). It's also needed in write mode to avoid new
+ * anon_vmas to be associated with existing vmas.
+ *
+ * A single task can't take more than one mm_take_all_locks() in a row
+ * or it would deadlock.
+ *
+ * The LSB in anon_vma->head.next and the AS_MM_ALL_LOCKS bitflag in
+ * mapping->flags avoid to take the same lock twice, if more than one
+ * vma in this mm is backed by the same anon_vma or address_space.
+ *
+ * We can take all the locks in random order because the VM code
+ * taking i_mmap_lock or anon_vma->lock outside the mmap_sem never
+ * takes more than one of them in a row. Secondly we're protected
+ * against a concurrent mm_take_all_locks() by the mm_all_locks_mutex.
+ *
+ * mm_take_all_locks() and mm_drop_all_locks are expensive operations
+ * that may have to take thousand of locks.
+ *
+ * mm_take_all_locks() can fail if it's interrupted by signals.
+ */
+int mm_take_all_locks(struct mm_struct *mm)
+{
+        struct vm_area_struct *vma;
+        int ret = -EINTR;
+
+        BUG_ON(down_read_trylock(&mm->mmap_sem));
+
+        mutex_lock(&mm_all_locks_mutex);
+
+        for (vma = mm->mmap; vma; vma = vma->vm_next) {
+                if (signal_pending(current))
+                        goto out_unlock;
+                if (vma->anon_vma)
+                        vm_lock_anon_vma(vma->anon_vma);
+                if (vma->vm_file && vma->vm_file->f_mapping)
+                        vm_lock_mapping(vma->vm_file->f_mapping);
+        }
+        ret = 0;
+
+out_unlock:
+        if (ret)
+                mm_drop_all_locks(mm);
+
+        return ret;
+}
+
+static void vm_unlock_anon_vma(struct anon_vma *anon_vma)
+{
+        if (test_bit(0, (unsigned long *) &anon_vma->head.next)) {
+                /*
+                 * The LSB of head.next can't change to 0 from under
+                 * us because we hold the mm_all_locks_mutex.
+                 *
+                 * We must however clear the bitflag before unlocking
+                 * the vma so the users using the anon_vma->head will
+                 * never see our bitflag.
+                 *
+                 * No need of atomic instructions here, head.next
+                 * can't change from under us until we release the
+                 * anon_vma->lock.
+                 */
+                if (!__test_and_clear_bit(0, (unsigned long *)
+                                          &anon_vma->head.next))
+                        BUG();
+                spin_unlock(&anon_vma->lock);
+        }
+}
+
+static void vm_unlock_mapping(struct address_space *mapping)
+{
+        if (test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
+                /*
+                 * AS_MM_ALL_LOCKS can't change to 0 from under us
+                 * because we hold the mm_all_locks_mutex.
+                 */
+                spin_unlock(&mapping->i_mmap_lock);
+                if (!test_and_clear_bit(AS_MM_ALL_LOCKS,
+                                        &mapping->flags))
+                        BUG();
+        }
+}
+
+/*
+ * The mmap_sem cannot be released by the caller until
+ * mm_drop_all_locks() returns.
+ */
+void mm_drop_all_locks(struct mm_struct *mm)
+{
+        struct vm_area_struct *vma;
+
+        BUG_ON(down_read_trylock(&mm->mmap_sem));
+        BUG_ON(!mutex_is_locked(&mm_all_locks_mutex));
+
+        for (vma = mm->mmap; vma; vma = vma->vm_next) {
+                if (vma->anon_vma)
+                        vm_unlock_anon_vma(vma->anon_vma);
+                if (vma->vm_file && vma->vm_file->f_mapping)
+                        vm_unlock_mapping(vma->vm_file->f_mapping);
+        }
+
+        mutex_unlock(&mm_all_locks_mutex);
+}