mm/madvise.c

   1 /*
   2  *      linux/mm/madvise.c
   3  *
   4  * Copyright (C) 1999  Linus Torvalds
   5  * Copyright (C) 2002  Christoph Hellwig
   6  */
   7
   8 #include <linux/mman.h>
   9 #include <linux/pagemap.h>
  10 #include <linux/syscalls.h>
  11 #include <linux/mempolicy.h>
  12 #include <linux/page-isolation.h>
  13 #include <linux/hugetlb.h>
  14 #include <linux/falloc.h>
  15 #include <linux/sched.h>
  16 #include <linux/ksm.h>
  17 #include <linux/fs.h>
  18 #include <linux/file.h>
  19 #include <linux/blkdev.h>
  20 #include <linux/backing-dev.h>
  21 #include <linux/swap.h>
  22 #include <linux/swapops.h>
  23 #include <linux/mmu_notifier.h>
  24
  25 #include <asm/tlb.h>
  26
  27 /*
  28  * Any behaviour which results in changes to the vma->vm_flags needs to
  29  * take mmap_sem for writing. Others, which simply traverse vmas, need
  30  * to only take it for reading.
  31  */
  32 static int madvise_need_mmap_write(int behavior)
  33 {
  34         switch (behavior) {
  35         case MADV_REMOVE:
  36         case MADV_WILLNEED:
  37         case MADV_DONTNEED:
  38         case MADV_FREE:
  39                 return 0;
  40         default:
  41                 /* be safe, default to 1. list exceptions explicitly */
  42                 return 1;
  43         }
  44 }
  45
  46 /*
  47  * We can potentially split a vm area into separate
  48  * areas, each area with its own behavior.
  49  */
  50 static long madvise_behavior(struct vm_area_struct *vma,
  51                      struct vm_area_struct **prev,
  52                      unsigned long start, unsigned long end, int behavior)
  53 {
  54         struct mm_struct *mm = vma->vm_mm;
  55         int error = 0;
  56         pgoff_t pgoff;
  57         unsigned long new_flags = vma->vm_flags;
  58
  59         switch (behavior) {
  60         case MADV_NORMAL:
  61                 new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
  62                 break;
  63         case MADV_SEQUENTIAL:
  64                 new_flags = (new_flags & ~VM_RAND_READ) | VM_SEQ_READ;
  65                 break;
  66         case MADV_RANDOM:
  67                 new_flags = (new_flags & ~VM_SEQ_READ) | VM_RAND_READ;
  68                 break;
  69         case MADV_DONTFORK:
  70                 new_flags |= VM_DONTCOPY;
  71                 break;
  72         case MADV_DOFORK:
  73                 if (vma->vm_flags & VM_IO) {
  74                         error = -EINVAL;
  75                         goto out;
  76                 }
  77                 new_flags &= ~VM_DONTCOPY;
  78                 break;
  79         case MADV_DONTDUMP:
  80                 new_flags |= VM_DONTDUMP;
  81                 break;
  82         case MADV_DODUMP:
  83                 if (new_flags & VM_SPECIAL) {
  84                         error = -EINVAL;
  85                         goto out;
  86                 }
  87                 new_flags &= ~VM_DONTDUMP;
  88                 break;
  89         case MADV_MERGEABLE:
  90         case MADV_UNMERGEABLE:
  91                 error = ksm_madvise(vma, start, end, behavior, &new_flags);
  92                 if (error)
  93                         goto out;
  94                 break;
  95         case MADV_HUGEPAGE:
  96         case MADV_NOHUGEPAGE:
  97                 error = hugepage_madvise(vma, &new_flags, behavior);
  98                 if (error)
  99                         goto out;
 100                 break;
 101         }
 102
 103         if (new_flags == vma->vm_flags) {
 104                 *prev = vma;
 105                 goto out;
 106         }
 107
 108         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 109         *prev = vma_merge(mm, *prev, start, end, new_flags, vma->anon_vma,
 110                           vma->vm_file, pgoff, vma_policy(vma),
 111                           vma->vm_userfaultfd_ctx);
 112         if (*prev) {
 113                 vma = *prev;
 114                 goto success;
 115         }
 116
 117         *prev = vma;
 118
 119         if (start != vma->vm_start) {
 120                 error = split_vma(mm, vma, start, 1);
 121                 if (error)
 122                         goto out;
 123         }
 124
 125         if (end != vma->vm_end) {
 126                 error = split_vma(mm, vma, end, 0);
 127                 if (error)
 128                         goto out;
 129         }
 130
 131 success:
 132         /*
 133          * vm_flags is protected by the mmap_sem held in write mode.
 134          */
 135         vma->vm_flags = new_flags;
 136
 137 out:
 138         if (error == -ENOMEM)
 139                 error = -EAGAIN;
 140         return error;
 141 }
 142
 143 #ifdef CONFIG_SWAP
 144 static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
 145         unsigned long end, struct mm_walk *walk)
 146 {
 147         pte_t *orig_pte;
 148         struct vm_area_struct *vma = walk->private;
 149         unsigned long index;
 150
 151         if (pmd_none_or_trans_huge_or_clear_bad(pmd))
 152                 return 0;
 153
 154         for (index = start; index != end; index += PAGE_SIZE) {
 155                 pte_t pte;
 156                 swp_entry_t entry;
 157                 struct page *page;
 158                 spinlock_t *ptl;
 159
 160                 orig_pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
 161                 pte = *(orig_pte + ((index - start) / PAGE_SIZE));
 162                 pte_unmap_unlock(orig_pte, ptl);
 163
 164                 if (pte_present(pte) || pte_none(pte))
 165                         continue;
 166                 entry = pte_to_swp_entry(pte);
 167                 if (unlikely(non_swap_entry(entry)))
 168                         continue;
 169
 170                 page = read_swap_cache_async(entry, GFP_HIGHUSER_MOVABLE,
 171                                                                 vma, index);
 172                 if (page)
 173                         page_cache_release(page);
 174         }
 175
 176         return 0;
 177 }
 178
 179 static void force_swapin_readahead(struct vm_area_struct *vma,
 180                 unsigned long start, unsigned long end)
 181 {
 182         struct mm_walk walk = {
 183                 .mm = vma->vm_mm,
 184                 .pmd_entry = swapin_walk_pmd_entry,
 185                 .private = vma,
 186         };
 187
 188         walk_page_range(start, end, &walk);
 189
 190         lru_add_drain();        /* Push any new pages onto the LRU now */
 191 }
 192
 193 static void force_shm_swapin_readahead(struct vm_area_struct *vma,
 194                 unsigned long start, unsigned long end,
 195                 struct address_space *mapping)
 196 {
 197         pgoff_t index;
 198         struct page *page;
 199         swp_entry_t swap;
 200
 201         for (; start < end; start += PAGE_SIZE) {
 202                 index = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 203
 204                 page = find_get_entry(mapping, index);
 205                 if (!radix_tree_exceptional_entry(page)) {
 206                         if (page)
 207                                 page_cache_release(page);
 208                         continue;
 209                 }
 210                 swap = radix_to_swp_entry(page);
 211                 page = read_swap_cache_async(swap, GFP_HIGHUSER_MOVABLE,
 212                                                                 NULL, 0);
 213                 if (page)
 214                         page_cache_release(page);
 215         }
 216
 217         lru_add_drain();        /* Push any new pages onto the LRU now */
 218 }
 219 #endif          /* CONFIG_SWAP */
 220
 221 /*
 222  * Schedule all required I/O operations.  Do not wait for completion.
 223  */
 224 static long madvise_willneed(struct vm_area_struct *vma,
 225                              struct vm_area_struct **prev,
 226                              unsigned long start, unsigned long end)
 227 {
 228         struct file *file = vma->vm_file;
 229
 230 #ifdef CONFIG_SWAP
 231         if (!file) {
 232                 *prev = vma;
 233                 force_swapin_readahead(vma, start, end);
 234                 return 0;
 235         }
 236
 237         if (shmem_mapping(file->f_mapping)) {
 238                 *prev = vma;
 239                 force_shm_swapin_readahead(vma, start, end,
 240                                         file->f_mapping);
 241                 return 0;
 242         }
 243 #else
 244         if (!file)
 245                 return -EBADF;
 246 #endif
 247
 248         if (IS_DAX(file_inode(file))) {
 249                 /* no bad return value, but ignore advice */
 250                 return 0;
 251         }
 252
 253         *prev = vma;
 254         start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 255         if (end > vma->vm_end)
 256                 end = vma->vm_end;
 257         end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 258
 259         force_page_cache_readahead(file->f_mapping, file, start, end - start);
 260         return 0;
 261 }
 262
 263 static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 264                                 unsigned long end, struct mm_walk *walk)
 265
 266 {
 267         struct mmu_gather *tlb = walk->private;
 268         struct mm_struct *mm = tlb->mm;
 269         struct vm_area_struct *vma = walk->vma;
 270         spinlock_t *ptl;
 271         pte_t *pte, ptent;
 272         struct page *page;
 273         swp_entry_t entry;
 274         unsigned long next;
 275         int nr_swap = 0;
 276
 277         next = pmd_addr_end(addr, end);
 278         if (pmd_trans_huge(*pmd)) {
 279                 if (next - addr != HPAGE_PMD_SIZE)
 280                         split_huge_pmd(vma, pmd, addr);
 281                 else if (!madvise_free_huge_pmd(tlb, vma, pmd, addr))
 282                         goto next;
 283                 /* fall through */
 284         }
 285
 286         if (pmd_trans_unstable(pmd))
 287                 return 0;
 288
 289         pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
 290         arch_enter_lazy_mmu_mode();
 291         for (; addr != end; pte++, addr += PAGE_SIZE) {
 292                 ptent = *pte;
 293
 294                 if (pte_none(ptent))
 295                         continue;
 296                 /*
 297                  * If the pte has swp_entry, just clear page table to
 298                  * prevent swap-in which is more expensive rather than
 299                  * (page allocation + zeroing).
 300                  */
 301                 if (!pte_present(ptent)) {
 302                         entry = pte_to_swp_entry(ptent);
 303                         if (non_swap_entry(entry))
 304                                 continue;
 305                         nr_swap--;
 306                         free_swap_and_cache(entry);
 307                         pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
 308                         continue;
 309                 }
 310
 311                 page = vm_normal_page(vma, addr, ptent);
 312                 if (!page)
 313                         continue;
 314
 315                 if (PageSwapCache(page) || PageDirty(page)) {
 316                         if (!trylock_page(page))
 317                                 continue;
 318                         /*
 319                          * If page is shared with others, we couldn't clear
 320                          * PG_dirty of the page.
 321                          */
 322                         if (page_count(page) != 1 + !!PageSwapCache(page)) {
 323                                 unlock_page(page);
 324                                 continue;
 325                         }
 326
 327                         if (PageSwapCache(page) && !try_to_free_swap(page)) {
 328                                 unlock_page(page);
 329                                 continue;
 330                         }
 331
 332                         ClearPageDirty(page);
 333                         unlock_page(page);
 334                 }
 335
 336                 /*
 337                  * Some of architecture(ex, PPC) don't update TLB
 338                  * with set_pte_at and tlb_remove_tlb_entry so for
 339                  * the portability, remap the pte with old|clean
 340                  * after pte clearing.
 341                  */
 342                 ptent = ptep_get_and_clear_full(mm, addr, pte,
 343                                                 tlb->fullmm);
 344                 ptent = pte_mkold(ptent);
 345                 ptent = pte_mkclean(ptent);
 346                 set_pte_at(mm, addr, pte, ptent);
 347                 if (PageActive(page))
 348                         deactivate_page(page);
 349                 tlb_remove_tlb_entry(tlb, pte, addr);
 350         }
 351
 352         if (nr_swap) {
 353                 if (current->mm == mm)
 354                         sync_mm_rss(mm);
 355
 356                 add_mm_counter(mm, MM_SWAPENTS, nr_swap);
 357         }
 358
 359         arch_leave_lazy_mmu_mode();
 360         pte_unmap_unlock(pte - 1, ptl);
 361 next:
 362         cond_resched();
 363         return 0;
 364 }
 365
 366 static void madvise_free_page_range(struct mmu_gather *tlb,
 367                              struct vm_area_struct *vma,
 368                              unsigned long addr, unsigned long end)
 369 {
 370         struct mm_walk free_walk = {
 371                 .pmd_entry = madvise_free_pte_range,
 372                 .mm = vma->vm_mm,
 373                 .private = tlb,
 374         };
 375
 376         BUG_ON(addr >= end);
 377         tlb_start_vma(tlb, vma);
 378         walk_page_range(addr, end, &free_walk);
 379         tlb_end_vma(tlb, vma);
 380 }
 381
 382 static int madvise_free_single_vma(struct vm_area_struct *vma,
 383                         unsigned long start_addr, unsigned long end_addr)
 384 {
 385         unsigned long start, end;
 386         struct mm_struct *mm = vma->vm_mm;
 387         struct mmu_gather tlb;
 388
 389         if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
 390                 return -EINVAL;
 391
 392         /* MADV_FREE works for only anon vma at the moment */
 393         if (!vma_is_anonymous(vma))
 394                 return -EINVAL;
 395
 396         start = max(vma->vm_start, start_addr);
 397         if (start >= vma->vm_end)
 398                 return -EINVAL;
 399         end = min(vma->vm_end, end_addr);
 400         if (end <= vma->vm_start)
 401                 return -EINVAL;
 402
 403         lru_add_drain();
 404         tlb_gather_mmu(&tlb, mm, start, end);
 405         update_hiwater_rss(mm);
 406
 407         mmu_notifier_invalidate_range_start(mm, start, end);
 408         madvise_free_page_range(&tlb, vma, start, end);
 409         mmu_notifier_invalidate_range_end(mm, start, end);
 410         tlb_finish_mmu(&tlb, start, end);
 411
 412         return 0;
 413 }
 414
 415 static long madvise_free(struct vm_area_struct *vma,
 416                              struct vm_area_struct **prev,
 417                              unsigned long start, unsigned long end)
 418 {
 419         *prev = vma;
 420         return madvise_free_single_vma(vma, start, end);
 421 }
 422
 423 /*
 424  * Application no longer needs these pages.  If the pages are dirty,
 425  * it's OK to just throw them away.  The app will be more careful about
 426  * data it wants to keep.  Be sure to free swap resources too.  The
 427  * zap_page_range call sets things up for shrink_active_list to actually free
 428  * these pages later if no one else has touched them in the meantime,
 429  * although we could add these pages to a global reuse list for
 430  * shrink_active_list to pick up before reclaiming other pages.
 431  *
 432  * NB: This interface discards data rather than pushes it out to swap,
 433  * as some implementations do.  This has performance implications for
 434  * applications like large transactional databases which want to discard
 435  * pages in anonymous maps after committing to backing store the data
 436  * that was kept in them.  There is no reason to write this data out to
 437  * the swap area if the application is discarding it.
 438  *
 439  * An interface that causes the system to free clean pages and flush
 440  * dirty pages is already available as msync(MS_INVALIDATE).
 441  */
 442 static long madvise_dontneed(struct vm_area_struct *vma,
 443                              struct vm_area_struct **prev,
 444                              unsigned long start, unsigned long end)
 445 {
 446         *prev = vma;
 447         if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
 448                 return -EINVAL;
 449
 450         zap_page_range(vma, start, end - start, NULL);
 451         return 0;
 452 }
 453
 454 /*
 455  * Application wants to free up the pages and associated backing store.
 456  * This is effectively punching a hole into the middle of a file.
 457  */
 458 static long madvise_remove(struct vm_area_struct *vma,
 459                                 struct vm_area_struct **prev,
 460                                 unsigned long start, unsigned long end)
 461 {
 462         loff_t offset;
 463         int error;
 464         struct file *f;
 465
 466         *prev = NULL;   /* tell sys_madvise we drop mmap_sem */
 467
 468         if (vma->vm_flags & VM_LOCKED)
 469                 return -EINVAL;
 470
 471         f = vma->vm_file;
 472
 473         if (!f || !f->f_mapping || !f->f_mapping->host) {
 474                         return -EINVAL;
 475         }
 476
 477         if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) != (VM_SHARED|VM_WRITE))
 478                 return -EACCES;
 479
 480         offset = (loff_t)(start - vma->vm_start)
 481                         + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
 482
 483         /*
 484          * Filesystem's fallocate may need to take i_mutex.  We need to
 485          * explicitly grab a reference because the vma (and hence the
 486          * vma's reference to the file) can go away as soon as we drop
 487          * mmap_sem.
 488          */
 489         get_file(f);
 490         up_read(&current->mm->mmap_sem);
 491         error = vfs_fallocate(f,
 492                                 FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
 493                                 offset, end - start);
 494         fput(f);
 495         down_read(&current->mm->mmap_sem);
 496         return error;
 497 }
 498
 499 #ifdef CONFIG_MEMORY_FAILURE
 500 /*
 501  * Error injection support for memory error handling.
 502  */
 503 static int madvise_hwpoison(int bhv, unsigned long start, unsigned long end)
 504 {
 505         struct page *p;
 506         if (!capable(CAP_SYS_ADMIN))
 507                 return -EPERM;
 508         for (; start < end; start += PAGE_SIZE <<
 509                                 compound_order(compound_head(p))) {
 510                 int ret;
 511
 512                 ret = get_user_pages_fast(start, 1, 0, &p);
 513                 if (ret != 1)
 514                         return ret;
 515
 516                 if (PageHWPoison(p)) {
 517                         put_page(p);
 518                         continue;
 519                 }
 520                 if (bhv == MADV_SOFT_OFFLINE) {
 521                         pr_info("Soft offlining page %#lx at %#lx\n",
 522                                 page_to_pfn(p), start);
 523                         ret = soft_offline_page(p, MF_COUNT_INCREASED);
 524                         if (ret)
 525                                 return ret;
 526                         continue;
 527                 }
 528                 pr_info("Injecting memory failure for page %#lx at %#lx\n",
 529                        page_to_pfn(p), start);
 530                 /* Ignore return value for now */
 531                 memory_failure(page_to_pfn(p), 0, MF_COUNT_INCREASED);
 532         }
 533         return 0;
 534 }
 535 #endif
 536
 537 static long
 538 madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
 539                 unsigned long start, unsigned long end, int behavior)
 540 {
 541         switch (behavior) {
 542         case MADV_REMOVE:
 543                 return madvise_remove(vma, prev, start, end);
 544         case MADV_WILLNEED:
 545                 return madvise_willneed(vma, prev, start, end);
 546         case MADV_FREE:
 547                 /*
 548                  * XXX: In this implementation, MADV_FREE works like
 549                  * MADV_DONTNEED on swapless system or full swap.
 550                  */
 551                 if (get_nr_swap_pages() > 0)
 552                         return madvise_free(vma, prev, start, end);
 553                 /* passthrough */
 554         case MADV_DONTNEED:
 555                 return madvise_dontneed(vma, prev, start, end);
 556         default:
 557                 return madvise_behavior(vma, prev, start, end, behavior);
 558         }
 559 }
 560
 561 static bool
 562 madvise_behavior_valid(int behavior)
 563 {
 564         switch (behavior) {
 565         case MADV_DOFORK:
 566         case MADV_DONTFORK:
 567         case MADV_NORMAL:
 568         case MADV_SEQUENTIAL:
 569         case MADV_RANDOM:
 570         case MADV_REMOVE:
 571         case MADV_WILLNEED:
 572         case MADV_DONTNEED:
 573         case MADV_FREE:
 574 #ifdef CONFIG_KSM
 575         case MADV_MERGEABLE:
 576         case MADV_UNMERGEABLE:
 577 #endif
 578 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 579         case MADV_HUGEPAGE:
 580         case MADV_NOHUGEPAGE:
 581 #endif
 582         case MADV_DONTDUMP:
 583         case MADV_DODUMP:
 584                 return true;
 585
 586         default:
 587                 return false;
 588         }
 589 }
 590
 591 /*
 592  * The madvise(2) system call.
 593  *
 594  * Applications can use madvise() to advise the kernel how it should
 595  * handle paging I/O in this VM area.  The idea is to help the kernel
 596  * use appropriate read-ahead and caching techniques.  The information
 597  * provided is advisory only, and can be safely disregarded by the
 598  * kernel without affecting the correct operation of the application.
 599  *
 600  * behavior values:
 601  *  MADV_NORMAL - the default behavior is to read clusters.  This
 602  *              results in some read-ahead and read-behind.
 603  *  MADV_RANDOM - the system should read the minimum amount of data
 604  *              on any access, since it is unlikely that the appli-
 605  *              cation will need more than what it asks for.
 606  *  MADV_SEQUENTIAL - pages in the given range will probably be accessed
 607  *              once, so they can be aggressively read ahead, and
 608  *              can be freed soon after they are accessed.
 609  *  MADV_WILLNEED - the application is notifying the system to read
 610  *              some pages ahead.
 611  *  MADV_DONTNEED - the application is finished with the given range,
 612  *              so the kernel can free resources associated with it.
 613  *  MADV_REMOVE - the application wants to free up the given range of
 614  *              pages and associated backing store.
 615  *  MADV_DONTFORK - omit this area from child's address space when forking:
 616  *              typically, to avoid COWing pages pinned by get_user_pages().
 617  *  MADV_DOFORK - cancel MADV_DONTFORK: no longer omit this area when forking.
 618  *  MADV_MERGEABLE - the application recommends that KSM try to merge pages in
 619  *              this area with pages of identical content from other such areas.
 620  *  MADV_UNMERGEABLE- cancel MADV_MERGEABLE: no longer merge pages with others.
 621  *
 622  * return values:
 623  *  zero    - success
 624  *  -EINVAL - start + len < 0, start is not page-aligned,
 625  *              "behavior" is not a valid value, or application
 626  *              is attempting to release locked or shared pages.
 627  *  -ENOMEM - addresses in the specified range are not currently
 628  *              mapped, or are outside the AS of the process.
 629  *  -EIO    - an I/O error occurred while paging in data.
 630  *  -EBADF  - map exists, but area maps something that isn't a file.
 631  *  -EAGAIN - a kernel resource was temporarily unavailable.
 632  */
 633 SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
 634 {
 635         unsigned long end, tmp;
 636         struct vm_area_struct *vma, *prev;
 637         int unmapped_error = 0;
 638         int error = -EINVAL;
 639         int write;
 640         size_t len;
 641         struct blk_plug plug;
 642
 643 #ifdef CONFIG_MEMORY_FAILURE
 644         if (behavior == MADV_HWPOISON || behavior == MADV_SOFT_OFFLINE)
 645                 return madvise_hwpoison(behavior, start, start+len_in);
 646 #endif
 647         if (!madvise_behavior_valid(behavior))
 648                 return error;
 649
 650         if (start & ~PAGE_MASK)
 651                 return error;
 652         len = (len_in + ~PAGE_MASK) & PAGE_MASK;
 653
 654         /* Check to see whether len was rounded up from small -ve to zero */
 655         if (len_in && !len)
 656                 return error;
 657
 658         end = start + len;
 659         if (end < start)
 660                 return error;
 661
 662         error = 0;
 663         if (end == start)
 664                 return error;
 665
 666         write = madvise_need_mmap_write(behavior);
 667         if (write)
 668                 down_write(&current->mm->mmap_sem);
 669         else
 670                 down_read(&current->mm->mmap_sem);
 671
 672         /*
 673          * If the interval [start,end) covers some unmapped address
 674          * ranges, just ignore them, but return -ENOMEM at the end.
 675          * - different from the way of handling in mlock etc.
 676          */
 677         vma = find_vma_prev(current->mm, start, &prev);
 678         if (vma && start > vma->vm_start)
 679                 prev = vma;
 680
 681         blk_start_plug(&plug);
 682         for (;;) {
 683                 /* Still start < end. */
 684                 error = -ENOMEM;
 685                 if (!vma)
 686                         goto out;
 687
 688                 /* Here start < (end|vma->vm_end). */
 689                 if (start < vma->vm_start) {
 690                         unmapped_error = -ENOMEM;
 691                         start = vma->vm_start;
 692                         if (start >= end)
 693                                 goto out;
 694                 }
 695
 696                 /* Here vma->vm_start <= start < (end|vma->vm_end) */
 697                 tmp = vma->vm_end;
 698                 if (end < tmp)
 699                         tmp = end;
 700
 701                 /* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
 702                 error = madvise_vma(vma, &prev, start, tmp, behavior);
 703                 if (error)
 704                         goto out;
 705                 start = tmp;
 706                 if (prev && start < prev->vm_end)
 707                         start = prev->vm_end;
 708                 error = unmapped_error;
 709                 if (start >= end)
 710                         goto out;
 711                 if (prev)
 712                         vma = prev->vm_next;
 713                 else    /* madvise_remove dropped mmap_sem */
 714                         vma = find_vma(current->mm, start);
 715         }
 716 out:
 717         blk_finish_plug(&plug);
 718         if (write)
 719                 up_write(&current->mm->mmap_sem);
 720         else
 721                 up_read(&current->mm->mmap_sem);
 722
 723         return error;
 724 }