diff options
Diffstat (limited to 'mm/mremap.c')
| -rw-r--r-- | mm/mremap.c | 57 |
1 files changed, 39 insertions, 18 deletions
diff --git a/mm/mremap.c b/mm/mremap.c index 5588bb6..3b639a4 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -71,26 +71,42 @@ static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma, static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, unsigned long old_addr, unsigned long old_end, struct vm_area_struct *new_vma, pmd_t *new_pmd, - unsigned long new_addr) + unsigned long new_addr, bool need_rmap_locks) { struct address_space *mapping = NULL; - struct anon_vma *anon_vma = vma->anon_vma; + struct anon_vma *anon_vma = NULL; struct mm_struct *mm = vma->vm_mm; pte_t *old_pte, *new_pte, pte; spinlock_t *old_ptl, *new_ptl; - if (vma->vm_file) { - /* - * Subtle point from Rajesh Venkatasubramanian: before - * moving file-based ptes, we must lock truncate_pagecache - * out, since it might clean the dst vma before the src vma, - * and we propagate stale pages into the dst afterward. - */ - mapping = vma->vm_file->f_mapping; - mutex_lock(&mapping->i_mmap_mutex); + /* + * When need_rmap_locks is true, we take the i_mmap_mutex and anon_vma + * locks to ensure that rmap will always observe either the old or the + * new ptes. This is the easiest way to avoid races with + * truncate_pagecache(), page migration, etc... + * + * When need_rmap_locks is false, we use other ways to avoid + * such races: + * + * - During exec() shift_arg_pages(), we use a specially tagged vma + * which rmap call sites look for using is_vma_temporary_stack(). + * + * - During mremap(), new_vma is often known to be placed after vma + * in rmap traversal order. This ensures rmap will always observe + * either the old pte, or the new pte, or both (the page table locks + * serialize access to individual ptes, but only rmap traversal + * order guarantees that we won't miss both the old and new ptes). + */ + if (need_rmap_locks) { + if (vma->vm_file) { + mapping = vma->vm_file->f_mapping; + mutex_lock(&mapping->i_mmap_mutex); + } + if (vma->anon_vma) { + anon_vma = vma->anon_vma; + anon_vma_lock(anon_vma); + } } - if (anon_vma) - anon_vma_lock(anon_vma); /* * We don't have to worry about the ordering of src and dst @@ -127,7 +143,8 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, unsigned long move_page_tables(struct vm_area_struct *vma, unsigned long old_addr, struct vm_area_struct *new_vma, - unsigned long new_addr, unsigned long len) + unsigned long new_addr, unsigned long len, + bool need_rmap_locks) { unsigned long extent, next, old_end; pmd_t *old_pmd, *new_pmd; @@ -174,7 +191,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma, if (extent > LATENCY_LIMIT) extent = LATENCY_LIMIT; move_ptes(vma, old_pmd, old_addr, old_addr + extent, - new_vma, new_pmd, new_addr); + new_vma, new_pmd, new_addr, need_rmap_locks); need_flush = true; } if (likely(need_flush)) @@ -198,6 +215,7 @@ static unsigned long move_vma(struct vm_area_struct *vma, unsigned long hiwater_vm; int split = 0; int err; + bool need_rmap_locks; /* * We'd prefer to avoid failure later on in do_munmap: @@ -219,18 +237,21 @@ static unsigned long move_vma(struct vm_area_struct *vma, return err; new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT); - new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff); + new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff, + &need_rmap_locks); if (!new_vma) return -ENOMEM; - moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len); + moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len, + need_rmap_locks); if (moved_len < old_len) { /* * On error, move entries back from new area to old, * which will succeed since page tables still there, * and then proceed to unmap new area instead of old. */ - move_page_tables(new_vma, new_addr, vma, old_addr, moved_len); + move_page_tables(new_vma, new_addr, vma, old_addr, moved_len, + true); vma = new_vma; old_len = new_len; old_addr = new_addr; |
