return get_compound_page_dtor(page_head) == free_huge_page;
}
+/*
+ * Find address_space associated with hugetlbfs page.
+ * Upon entry page is locked and page 'was' mapped although mapped state
+ * could change. If necessary, use anon_vma to find vma and associated
+ * address space. The returned mapping may be stale, but it can not be
+ * invalid as page lock (which is held) is required to destroy mapping.
+ */
+static struct address_space *_get_hugetlb_page_mapping(struct page *hpage)
+{
+ struct anon_vma *anon_vma;
+ pgoff_t pgoff_start, pgoff_end;
+ struct anon_vma_chain *avc;
+ struct address_space *mapping = page_mapping(hpage);
+
+ /* Simple file based mapping */
+ if (mapping)
+ return mapping;
+
+ /*
+ * Even anonymous hugetlbfs mappings are associated with an
+ * underlying hugetlbfs file (see hugetlb_file_setup in mmap
+ * code). Find a vma associated with the anonymous vma, and
+ * use the file pointer to get address_space.
+ */
+ anon_vma = page_lock_anon_vma_read(hpage);
+ if (!anon_vma)
+ return mapping; /* NULL */
+
+ /* Use first found vma */
+ pgoff_start = page_to_pgoff(hpage);
+ pgoff_end = pgoff_start + hpage_nr_pages(hpage) - 1;
+ anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root,
+ pgoff_start, pgoff_end) {
+ struct vm_area_struct *vma = avc->vma;
+
+ mapping = vma->vm_file->f_mapping;
+ break;
+ }
+
+ anon_vma_unlock_read(anon_vma);
+ return mapping;
+}
+
+/*
+ * Find and lock address space (mapping) in write mode.
+ *
+ * Upon entry, the page is locked which allows us to find the mapping
+ * even in the case of an anon page. However, locking order dictates
+ * the i_mmap_rwsem be acquired BEFORE the page lock. This is hugetlbfs
+ * specific. So, we first try to lock the sema while still holding the
+ * page lock. If this works, great! If not, then we need to drop the
+ * page lock and then acquire i_mmap_rwsem and reacquire page lock. Of
+ * course, need to revalidate state along the way.
+ */
+struct address_space *hugetlb_page_mapping_lock_write(struct page *hpage)
+{
+ struct address_space *mapping, *mapping2;
+
+ mapping = _get_hugetlb_page_mapping(hpage);
+retry:
+ if (!mapping)
+ return mapping;
+
+ /*
+ * If no contention, take lock and return
+ */
+ if (i_mmap_trylock_write(mapping))
+ return mapping;
+
+ /*
+ * Must drop page lock and wait on mapping sema.
+ * Note: Once page lock is dropped, mapping could become invalid.
+ * As a hack, increase map count until we lock page again.
+ */
+ atomic_inc(&hpage->_mapcount);
+ unlock_page(hpage);
+ i_mmap_lock_write(mapping);
+ lock_page(hpage);
+ atomic_add_negative(-1, &hpage->_mapcount);
+
+ /* verify page is still mapped */
+ if (!page_mapped(hpage)) {
+ i_mmap_unlock_write(mapping);
+ return NULL;
+ }
+
+ /*
+ * Get address space again and verify it is the same one
+ * we locked. If not, drop lock and retry.
+ */
+ mapping2 = _get_hugetlb_page_mapping(hpage);
+ if (mapping2 != mapping) {
+ i_mmap_unlock_write(mapping);
+ mapping = mapping2;
+ goto retry;
+ }
+
+ return mapping;
+}
+
pgoff_t __basepage_index(struct page *page)
{
struct page *page_head = compound_head(page);
int cow;
struct hstate *h = hstate_vma(vma);
unsigned long sz = huge_page_size(h);
+ struct address_space *mapping = vma->vm_file->f_mapping;
struct mmu_notifier_range range;
int ret = 0;
vma->vm_start,
vma->vm_end);
mmu_notifier_invalidate_range_start(&range);
+ } else {
+ /*
+ * For shared mappings i_mmap_rwsem must be held to call
+ * huge_pte_alloc, otherwise the returned ptep could go
+ * away if part of a shared pmd and another thread calls
+ * huge_pmd_unshare.
+ */
+ i_mmap_lock_read(mapping);
}
for (addr = vma->vm_start; addr < vma->vm_end; addr += sz) {
if (cow)
mmu_notifier_invalidate_range_end(&range);
+ else
+ i_mmap_unlock_read(mapping);
return ret;
}
};
/*
- * hugetlb_fault_mutex must be dropped before
- * handling userfault. Reacquire after handling
- * fault to make calling code simpler.
+ * hugetlb_fault_mutex and i_mmap_rwsem must be
+ * dropped before handling userfault. Reacquire
+ * after handling fault to make calling code simpler.
*/
hash = hugetlb_fault_mutex_hash(mapping, idx);
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
+ i_mmap_unlock_read(mapping);
ret = handle_userfault(&vmf, VM_UFFD_MISSING);
+ i_mmap_lock_read(mapping);
mutex_lock(&hugetlb_fault_mutex_table[hash]);
goto out;
}
ptep = huge_pte_offset(mm, haddr, huge_page_size(h));
if (ptep) {
+ /*
+ * Since we hold no locks, ptep could be stale. That is
+ * OK as we are only making decisions based on content and
+ * not actually modifying content here.
+ */
entry = huge_ptep_get(ptep);
if (unlikely(is_hugetlb_entry_migration(entry))) {
migration_entry_wait_huge(vma, mm, ptep);
return VM_FAULT_OOM;
}
+ /*
+ * Acquire i_mmap_rwsem before calling huge_pte_alloc and hold
+ * until finished with ptep. This prevents huge_pmd_unshare from
+ * being called elsewhere and making the ptep no longer valid.
+ *
+ * ptep could have already be assigned via huge_pte_offset. That
+ * is OK, as huge_pte_alloc will return the same value unless
+ * something has changed.
+ */
mapping = vma->vm_file->f_mapping;
- idx = vma_hugecache_offset(h, vma, haddr);
+ i_mmap_lock_read(mapping);
+ ptep = huge_pte_alloc(mm, haddr, huge_page_size(h));
+ if (!ptep) {
+ i_mmap_unlock_read(mapping);
+ return VM_FAULT_OOM;
+ }
/*
* Serialize hugepage allocation and instantiation, so that we don't
* get spurious allocation failures if two CPUs race to instantiate
* the same page in the page cache.
*/
+ idx = vma_hugecache_offset(h, vma, haddr);
hash = hugetlb_fault_mutex_hash(mapping, idx);
mutex_lock(&hugetlb_fault_mutex_table[hash]);
}
out_mutex:
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
+ i_mmap_unlock_read(mapping);
/*
* Generally it's safe to hold refcount during waiting page lock. But
* here we just wait to defer the next page fault to avoid busy loop and
* Search for a shareable pmd page for hugetlb. In any case calls pmd_alloc()
* and returns the corresponding pte. While this is not necessary for the
* !shared pmd case because we can allocate the pmd later as well, it makes the
- * code much cleaner. pmd allocation is essential for the shared case because
- * pud has to be populated inside the same i_mmap_rwsem section - otherwise
- * racing tasks could either miss the sharing (see huge_pte_offset) or select a
- * bad pmd for sharing.
+ * code much cleaner.
+ *
+ * This routine must be called with i_mmap_rwsem held in at least read mode.
+ * For hugetlbfs, this prevents removal of any page table entries associated
+ * with the address space. This is important as we are setting up sharing
+ * based on existing page table entries (mappings).
*/
pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
{
if (!vma_shareable(vma, addr))
return (pte_t *)pmd_alloc(mm, pud, addr);
- i_mmap_lock_read(mapping);
vma_interval_tree_foreach(svma, &mapping->i_mmap, idx, idx) {
if (svma == vma)
continue;
spin_unlock(ptl);
out:
pte = (pte_t *)pmd_alloc(mm, pud, addr);
- i_mmap_unlock_read(mapping);
return pte;
}
* indicated by page_count > 1, unmap is achieved by clearing pud and
* decrementing the ref count. If count == 1, the pte page is not shared.
*
- * called with page table lock held.
+ * Called with page table lock held and i_mmap_rwsem held in write mode.
*
* returns: 1 successfully unmapped a shared pte page
* 0 the underlying pte page is not shared, or it is the last user
projects / linux-2.6-microblaze.git / commitdiff