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 *orig_pte, *pte, ptent;
 272         struct page *page;
 273
 274         split_huge_pmd(vma, pmd, addr);
 275         if (pmd_trans_unstable(pmd))
 276                 return 0;
 277
 278         orig_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
 279         arch_enter_lazy_mmu_mode();
 280         for (; addr != end; pte++, addr += PAGE_SIZE) {
 281                 ptent = *pte;
 282
 283                 if (!pte_present(ptent))
 284                         continue;
 285
 286                 page = vm_normal_page(vma, addr, ptent);
 287                 if (!page)
 288                         continue;
 289
 290                 /*
 291                  * If pmd isn't transhuge but the page is THP and
 292                  * is owned by only this process, split it and
 293                  * deactivate all pages.
 294                  */
 295                 if (PageTransCompound(page)) {
 296                         if (page_mapcount(page) != 1)
 297                                 goto out;
 298                         get_page(page);
 299                         if (!trylock_page(page)) {
 300                                 put_page(page);
 301                                 goto out;
 302                         }
 303                         pte_unmap_unlock(orig_pte, ptl);
 304                         if (split_huge_page(page)) {
 305                                 unlock_page(page);
 306                                 put_page(page);
 307                                 pte_offset_map_lock(mm, pmd, addr, &ptl);
 308                                 goto out;
 309                         }
 310                         put_page(page);
 311                         unlock_page(page);
 312                         pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
 313                         pte--;
 314                         addr -= PAGE_SIZE;
 315                         continue;
 316                 }
 317
 318                 VM_BUG_ON_PAGE(PageTransCompound(page), page);
 319
 320                 if (PageSwapCache(page) || PageDirty(page)) {
 321                         if (!trylock_page(page))
 322                                 continue;
 323                         /*
 324                          * If page is shared with others, we couldn't clear
 325                          * PG_dirty of the page.
 326                          */
 327                         if (page_mapcount(page) != 1) {
 328                                 unlock_page(page);
 329                                 continue;
 330                         }
 331
 332                         if (PageSwapCache(page) && !try_to_free_swap(page)) {
 333                                 unlock_page(page);
 334                                 continue;
 335                         }
 336
 337                         ClearPageDirty(page);
 338                         unlock_page(page);
 339                 }
 340
 341                 if (pte_young(ptent) || pte_dirty(ptent)) {
 342                         /*
 343                          * Some of architecture(ex, PPC) don't update TLB
 344                          * with set_pte_at and tlb_remove_tlb_entry so for
 345                          * the portability, remap the pte with old|clean
 346                          * after pte clearing.
 347                          */
 348                         ptent = ptep_get_and_clear_full(mm, addr, pte,
 349                                                         tlb->fullmm);
 350
 351                         ptent = pte_mkold(ptent);
 352                         ptent = pte_mkclean(ptent);
 353                         set_pte_at(mm, addr, pte, ptent);
 354                         tlb_remove_tlb_entry(tlb, pte, addr);
 355                 }
 356         }
 357 out:
 358         arch_leave_lazy_mmu_mode();
 359         pte_unmap_unlock(orig_pte, ptl);
 360         cond_resched();
 361         return 0;
 362 }
 363
 364 static void madvise_free_page_range(struct mmu_gather *tlb,
 365                              struct vm_area_struct *vma,
 366                              unsigned long addr, unsigned long end)
 367 {
 368         struct mm_walk free_walk = {
 369                 .pmd_entry = madvise_free_pte_range,
 370                 .mm = vma->vm_mm,
 371                 .private = tlb,
 372         };
 373
 374         tlb_start_vma(tlb, vma);
 375         walk_page_range(addr, end, &free_walk);
 376         tlb_end_vma(tlb, vma);
 377 }
 378
 379 static int madvise_free_single_vma(struct vm_area_struct *vma,
 380                         unsigned long start_addr, unsigned long end_addr)
 381 {
 382         unsigned long start, end;
 383         struct mm_struct *mm = vma->vm_mm;
 384         struct mmu_gather tlb;
 385
 386         if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
 387                 return -EINVAL;
 388
 389         /* MADV_FREE works for only anon vma at the moment */
 390         if (!vma_is_anonymous(vma))
 391                 return -EINVAL;
 392
 393         start = max(vma->vm_start, start_addr);
 394         if (start >= vma->vm_end)
 395                 return -EINVAL;
 396         end = min(vma->vm_end, end_addr);
 397         if (end <= vma->vm_start)
 398                 return -EINVAL;
 399
 400         lru_add_drain();
 401         tlb_gather_mmu(&tlb, mm, start, end);
 402         update_hiwater_rss(mm);
 403
 404         mmu_notifier_invalidate_range_start(mm, start, end);
 405         madvise_free_page_range(&tlb, vma, start, end);
 406         mmu_notifier_invalidate_range_end(mm, start, end);
 407         tlb_finish_mmu(&tlb, start, end);
 408
 409         return 0;
 410 }
 411
 412 static long madvise_free(struct vm_area_struct *vma,
 413                              struct vm_area_struct **prev,
 414                              unsigned long start, unsigned long end)
 415 {
 416         *prev = vma;
 417         return madvise_free_single_vma(vma, start, end);
 418 }
 419
 420 /*
 421  * Application no longer needs these pages.  If the pages are dirty,
 422  * it's OK to just throw them away.  The app will be more careful about
 423  * data it wants to keep.  Be sure to free swap resources too.  The
 424  * zap_page_range call sets things up for shrink_active_list to actually free
 425  * these pages later if no one else has touched them in the meantime,
 426  * although we could add these pages to a global reuse list for
 427  * shrink_active_list to pick up before reclaiming other pages.
 428  *
 429  * NB: This interface discards data rather than pushes it out to swap,
 430  * as some implementations do.  This has performance implications for
 431  * applications like large transactional databases which want to discard
 432  * pages in anonymous maps after committing to backing store the data
 433  * that was kept in them.  There is no reason to write this data out to
 434  * the swap area if the application is discarding it.
 435  *
 436  * An interface that causes the system to free clean pages and flush
 437  * dirty pages is already available as msync(MS_INVALIDATE).
 438  */
 439 static long madvise_dontneed(struct vm_area_struct *vma,
 440                              struct vm_area_struct **prev,
 441                              unsigned long start, unsigned long end)
 442 {
 443         *prev = vma;
 444         if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
 445                 return -EINVAL;
 446
 447         zap_page_range(vma, start, end - start, NULL);
 448         return 0;
 449 }
 450
 451 /*
 452  * Application wants to free up the pages and associated backing store.
 453  * This is effectively punching a hole into the middle of a file.
 454  */
 455 static long madvise_remove(struct vm_area_struct *vma,
 456                                 struct vm_area_struct **prev,
 457                                 unsigned long start, unsigned long end)
 458 {
 459         loff_t offset;
 460         int error;
 461         struct file *f;
 462
 463         *prev = NULL;   /* tell sys_madvise we drop mmap_sem */
 464
 465         if (vma->vm_flags & VM_LOCKED)
 466                 return -EINVAL;
 467
 468         f = vma->vm_file;
 469
 470         if (!f || !f->f_mapping || !f->f_mapping->host) {
 471                         return -EINVAL;
 472         }
 473
 474         if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) != (VM_SHARED|VM_WRITE))
 475                 return -EACCES;
 476
 477         offset = (loff_t)(start - vma->vm_start)
 478                         + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
 479
 480         /*
 481          * Filesystem's fallocate may need to take i_mutex.  We need to
 482          * explicitly grab a reference because the vma (and hence the
 483          * vma's reference to the file) can go away as soon as we drop
 484          * mmap_sem.
 485          */
 486         get_file(f);
 487         up_read(&current->mm->mmap_sem);
 488         error = vfs_fallocate(f,
 489                                 FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
 490                                 offset, end - start);
 491         fput(f);
 492         down_read(&current->mm->mmap_sem);
 493         return error;
 494 }
 495
 496 #ifdef CONFIG_MEMORY_FAILURE
 497 /*
 498  * Error injection support for memory error handling.
 499  */
 500 static int madvise_hwpoison(int bhv, unsigned long start, unsigned long end)
 501 {
 502         struct page *p;
 503         if (!capable(CAP_SYS_ADMIN))
 504                 return -EPERM;
 505         for (; start < end; start += PAGE_SIZE <<
 506                                 compound_order(compound_head(p))) {
 507                 int ret;
 508
 509                 ret = get_user_pages_fast(start, 1, 0, &p);
 510                 if (ret != 1)
 511                         return ret;
 512
 513                 if (PageHWPoison(p)) {
 514                         put_page(p);
 515                         continue;
 516                 }
 517                 if (bhv == MADV_SOFT_OFFLINE) {
 518                         pr_info("Soft offlining page %#lx at %#lx\n",
 519                                 page_to_pfn(p), start);
 520                         ret = soft_offline_page(p, MF_COUNT_INCREASED);
 521                         if (ret)
 522                                 return ret;
 523                         continue;
 524                 }
 525                 pr_info("Injecting memory failure for page %#lx at %#lx\n",
 526                        page_to_pfn(p), start);
 527                 /* Ignore return value for now */
 528                 memory_failure(page_to_pfn(p), 0, MF_COUNT_INCREASED);
 529         }
 530         return 0;
 531 }
 532 #endif
 533
 534 static long
 535 madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
 536                 unsigned long start, unsigned long end, int behavior)
 537 {
 538         switch (behavior) {
 539         case MADV_REMOVE:
 540                 return madvise_remove(vma, prev, start, end);
 541         case MADV_WILLNEED:
 542                 return madvise_willneed(vma, prev, start, end);
 543         case MADV_FREE:
 544                 /*
 545                  * XXX: In this implementation, MADV_FREE works like
 546                  * MADV_DONTNEED on swapless system or full swap.
 547                  */
 548                 if (get_nr_swap_pages() > 0)
 549                         return madvise_free(vma, prev, start, end);
 550                 /* passthrough */
 551         case MADV_DONTNEED:
 552                 return madvise_dontneed(vma, prev, start, end);
 553         default:
 554                 return madvise_behavior(vma, prev, start, end, behavior);
 555         }
 556 }
 557
 558 static bool
 559 madvise_behavior_valid(int behavior)
 560 {
 561         switch (behavior) {
 562         case MADV_DOFORK:
 563         case MADV_DONTFORK:
 564         case MADV_NORMAL:
 565         case MADV_SEQUENTIAL:
 566         case MADV_RANDOM:
 567         case MADV_REMOVE:
 568         case MADV_WILLNEED:
 569         case MADV_DONTNEED:
 570         case MADV_FREE:
 571 #ifdef CONFIG_KSM
 572         case MADV_MERGEABLE:
 573         case MADV_UNMERGEABLE:
 574 #endif
 575 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 576         case MADV_HUGEPAGE:
 577         case MADV_NOHUGEPAGE:
 578 #endif
 579         case MADV_DONTDUMP:
 580         case MADV_DODUMP:
 581                 return true;
 582
 583         default:
 584                 return false;
 585         }
 586 }
 587
 588 /*
 589  * The madvise(2) system call.
 590  *
 591  * Applications can use madvise() to advise the kernel how it should
 592  * handle paging I/O in this VM area.  The idea is to help the kernel
 593  * use appropriate read-ahead and caching techniques.  The information
 594  * provided is advisory only, and can be safely disregarded by the
 595  * kernel without affecting the correct operation of the application.
 596  *
 597  * behavior values:
 598  *  MADV_NORMAL - the default behavior is to read clusters.  This
 599  *              results in some read-ahead and read-behind.
 600  *  MADV_RANDOM - the system should read the minimum amount of data
 601  *              on any access, since it is unlikely that the appli-
 602  *              cation will need more than what it asks for.
 603  *  MADV_SEQUENTIAL - pages in the given range will probably be accessed
 604  *              once, so they can be aggressively read ahead, and
 605  *              can be freed soon after they are accessed.
 606  *  MADV_WILLNEED - the application is notifying the system to read
 607  *              some pages ahead.
 608  *  MADV_DONTNEED - the application is finished with the given range,
 609  *              so the kernel can free resources associated with it.
 610  *  MADV_REMOVE - the application wants to free up the given range of
 611  *              pages and associated backing store.
 612  *  MADV_DONTFORK - omit this area from child's address space when forking:
 613  *              typically, to avoid COWing pages pinned by get_user_pages().
 614  *  MADV_DOFORK - cancel MADV_DONTFORK: no longer omit this area when forking.
 615  *  MADV_MERGEABLE - the application recommends that KSM try to merge pages in
 616  *              this area with pages of identical content from other such areas.
 617  *  MADV_UNMERGEABLE- cancel MADV_MERGEABLE: no longer merge pages with others.
 618  *
 619  * return values:
 620  *  zero    - success
 621  *  -EINVAL - start + len < 0, start is not page-aligned,
 622  *              "behavior" is not a valid value, or application
 623  *              is attempting to release locked or shared pages.
 624  *  -ENOMEM - addresses in the specified range are not currently
 625  *              mapped, or are outside the AS of the process.
 626  *  -EIO    - an I/O error occurred while paging in data.
 627  *  -EBADF  - map exists, but area maps something that isn't a file.
 628  *  -EAGAIN - a kernel resource was temporarily unavailable.
 629  */
 630 SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
 631 {
 632         unsigned long end, tmp;
 633         struct vm_area_struct *vma, *prev;
 634         int unmapped_error = 0;
 635         int error = -EINVAL;
 636         int write;
 637         size_t len;
 638         struct blk_plug plug;
 639
 640 #ifdef CONFIG_MEMORY_FAILURE
 641         if (behavior == MADV_HWPOISON || behavior == MADV_SOFT_OFFLINE)
 642                 return madvise_hwpoison(behavior, start, start+len_in);
 643 #endif
 644         if (!madvise_behavior_valid(behavior))
 645                 return error;
 646
 647         if (start & ~PAGE_MASK)
 648                 return error;
 649         len = (len_in + ~PAGE_MASK) & PAGE_MASK;
 650
 651         /* Check to see whether len was rounded up from small -ve to zero */
 652         if (len_in && !len)
 653                 return error;
 654
 655         end = start + len;
 656         if (end < start)
 657                 return error;
 658
 659         error = 0;
 660         if (end == start)
 661                 return error;
 662
 663         write = madvise_need_mmap_write(behavior);
 664         if (write)
 665                 down_write(&current->mm->mmap_sem);
 666         else
 667                 down_read(&current->mm->mmap_sem);
 668
 669         /*
 670          * If the interval [start,end) covers some unmapped address
 671          * ranges, just ignore them, but return -ENOMEM at the end.
 672          * - different from the way of handling in mlock etc.
 673          */
 674         vma = find_vma_prev(current->mm, start, &prev);
 675         if (vma && start > vma->vm_start)
 676                 prev = vma;
 677
 678         blk_start_plug(&plug);
 679         for (;;) {
 680                 /* Still start < end. */
 681                 error = -ENOMEM;
 682                 if (!vma)
 683                         goto out;
 684
 685                 /* Here start < (end|vma->vm_end). */
 686                 if (start < vma->vm_start) {
 687                         unmapped_error = -ENOMEM;
 688                         start = vma->vm_start;
 689                         if (start >= end)
 690                                 goto out;
 691                 }
 692
 693                 /* Here vma->vm_start <= start < (end|vma->vm_end) */
 694                 tmp = vma->vm_end;
 695                 if (end < tmp)
 696                         tmp = end;
 697
 698                 /* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
 699                 error = madvise_vma(vma, &prev, start, tmp, behavior);
 700                 if (error)
 701                         goto out;
 702                 start = tmp;
 703                 if (prev && start < prev->vm_end)
 704                         start = prev->vm_end;
 705                 error = unmapped_error;
 706                 if (start >= end)
 707                         goto out;
 708                 if (prev)
 709                         vma = prev->vm_next;
 710                 else    /* madvise_remove dropped mmap_sem */
 711                         vma = find_vma(current->mm, start);
 712         }
 713 out:
 714         blk_finish_plug(&plug);
 715         if (write)
 716                 up_write(&current->mm->mmap_sem);
 717         else
 718                 up_read(&current->mm->mmap_sem);
 719
 720         return error;
 721 }