ClabureDB: Classified Bug-Reports Database

 * 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->vm_file && vma->vm_file->f_mapping)
                        vm_lock_mapping(mm, vma->vm_file->f_mapping);
        }

        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                if (signal_pending(current))
                        goto out_unlock;
                if (vma->anon_vma)
                        vm_lock_anon_vma(mm, vma->anon_vma);
        }

        ret = 0;