mm/mlock.c

   1 /*
   2  *      linux/mm/mlock.c
   3  *
   4  *  (C) Copyright 1995 Linus Torvalds
   5  *  (C) Copyright 2002 Christoph Hellwig
   6  */
   7
   8 #include <linux/capability.h>
   9 #include <linux/mman.h>
  10 #include <linux/mm.h>
  11 #include <linux/swap.h>
  12 #include <linux/swapops.h>
  13 #include <linux/pagemap.h>
  14 #include <linux/mempolicy.h>
  15 #include <linux/syscalls.h>
  16 #include <linux/sched.h>
  17 #include <linux/module.h>
  18 #include <linux/rmap.h>
  19 #include <linux/mmzone.h>
  20 #include <linux/hugetlb.h>
  21
  22 #include "internal.h"
  23
  24 int can_do_mlock(void)
  25 {
  26         if (capable(CAP_IPC_LOCK))
  27                 return 1;
  28         if (current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur != 0)
  29                 return 1;
  30         return 0;
  31 }
  32 EXPORT_SYMBOL(can_do_mlock);
  33
  34 #ifdef CONFIG_UNEVICTABLE_LRU
  35 /*
  36  * Mlocked pages are marked with PageMlocked() flag for efficient testing
  37  * in vmscan and, possibly, the fault path; and to support semi-accurate
  38  * statistics.
  39  *
  40  * An mlocked page [PageMlocked(page)] is unevictable.  As such, it will
  41  * be placed on the LRU "unevictable" list, rather than the [in]active lists.
  42  * The unevictable list is an LRU sibling list to the [in]active lists.
  43  * PageUnevictable is set to indicate the unevictable state.
  44  *
  45  * When lazy mlocking via vmscan, it is important to ensure that the
  46  * vma's VM_LOCKED status is not concurrently being modified, otherwise we
  47  * may have mlocked a page that is being munlocked. So lazy mlock must take
  48  * the mmap_sem for read, and verify that the vma really is locked
  49  * (see mm/rmap.c).
  50  */
  51
  52 /*
  53  *  LRU accounting for clear_page_mlock()
  54  */
  55 void __clear_page_mlock(struct page *page)
  56 {
  57         VM_BUG_ON(!PageLocked(page));
  58
  59         if (!page->mapping) {   /* truncated ? */
  60                 return;
  61         }
  62
  63         dec_zone_page_state(page, NR_MLOCK);
  64         count_vm_event(UNEVICTABLE_PGCLEARED);
  65         if (!isolate_lru_page(page)) {
  66                 putback_lru_page(page);
  67         } else {
  68                 /*
  69                  * We lost the race. the page already moved to evictable list.
  70                  */
  71                 if (PageUnevictable(page))
  72                         count_vm_event(UNEVICTABLE_PGSTRANDED);
  73         }
  74 }
  75
  76 /*
  77  * Mark page as mlocked if not already.
  78  * If page on LRU, isolate and putback to move to unevictable list.
  79  */
  80 void mlock_vma_page(struct page *page)
  81 {
  82         BUG_ON(!PageLocked(page));
  83
  84         if (!TestSetPageMlocked(page)) {
  85                 inc_zone_page_state(page, NR_MLOCK);
  86                 count_vm_event(UNEVICTABLE_PGMLOCKED);
  87                 if (!isolate_lru_page(page))
  88                         putback_lru_page(page);
  89         }
  90 }
  91
  92 /*
  93  * called from munlock()/munmap() path with page supposedly on the LRU.
  94  *
  95  * Note:  unlike mlock_vma_page(), we can't just clear the PageMlocked
  96  * [in try_to_munlock()] and then attempt to isolate the page.  We must
  97  * isolate the page to keep others from messing with its unevictable
  98  * and mlocked state while trying to munlock.  However, we pre-clear the
  99  * mlocked state anyway as we might lose the isolation race and we might
 100  * not get another chance to clear PageMlocked.  If we successfully
 101  * isolate the page and try_to_munlock() detects other VM_LOCKED vmas
 102  * mapping the page, it will restore the PageMlocked state, unless the page
 103  * is mapped in a non-linear vma.  So, we go ahead and SetPageMlocked(),
 104  * perhaps redundantly.
 105  * If we lose the isolation race, and the page is mapped by other VM_LOCKED
 106  * vmas, we'll detect this in vmscan--via try_to_munlock() or try_to_unmap()
 107  * either of which will restore the PageMlocked state by calling
 108  * mlock_vma_page() above, if it can grab the vma's mmap sem.
 109  */
 110 static void munlock_vma_page(struct page *page)
 111 {
 112         BUG_ON(!PageLocked(page));
 113
 114         if (TestClearPageMlocked(page)) {
 115                 dec_zone_page_state(page, NR_MLOCK);
 116                 if (!isolate_lru_page(page)) {
 117                         int ret = try_to_munlock(page);
 118                         /*
 119                          * did try_to_unlock() succeed or punt?
 120                          */
 121                         if (ret == SWAP_SUCCESS || ret == SWAP_AGAIN)
 122                                 count_vm_event(UNEVICTABLE_PGMUNLOCKED);
 123
 124                         putback_lru_page(page);
 125                 } else {
 126                         /*
 127                          * We lost the race.  let try_to_unmap() deal
 128                          * with it.  At least we get the page state and
 129                          * mlock stats right.  However, page is still on
 130                          * the noreclaim list.  We'll fix that up when
 131                          * the page is eventually freed or we scan the
 132                          * noreclaim list.
 133                          */
 134                         if (PageUnevictable(page))
 135                                 count_vm_event(UNEVICTABLE_PGSTRANDED);
 136                         else
 137                                 count_vm_event(UNEVICTABLE_PGMUNLOCKED);
 138                 }
 139         }
 140 }
 141
 142 /**
 143  * __mlock_vma_pages_range() -  mlock/munlock a range of pages in the vma.
 144  * @vma:   target vma
 145  * @start: start address
 146  * @end:   end address
 147  * @mlock: 0 indicate munlock, otherwise mlock.
 148  *
 149  * If @mlock == 0, unlock an mlocked range;
 150  * else mlock the range of pages.  This takes care of making the pages present ,
 151  * too.
 152  *
 153  * return 0 on success, negative error code on error.
 154  *
 155  * vma->vm_mm->mmap_sem must be held for at least read.
 156  */
 157 static long __mlock_vma_pages_range(struct vm_area_struct *vma,
 158                                    unsigned long start, unsigned long end,
 159                                    int mlock)
 160 {
 161         struct mm_struct *mm = vma->vm_mm;
 162         unsigned long addr = start;
 163         struct page *pages[16]; /* 16 gives a reasonable batch */
 164         int nr_pages = (end - start) / PAGE_SIZE;
 165         int ret = 0;
 166         int gup_flags = 0;
 167
 168         VM_BUG_ON(start & ~PAGE_MASK);
 169         VM_BUG_ON(end   & ~PAGE_MASK);
 170         VM_BUG_ON(start < vma->vm_start);
 171         VM_BUG_ON(end   > vma->vm_end);
 172         VM_BUG_ON((!rwsem_is_locked(&mm->mmap_sem)) &&
 173                   (atomic_read(&mm->mm_users) != 0));
 174
 175         /*
 176          * mlock:   don't page populate if page has PROT_NONE permission.
 177          * munlock: the pages always do munlock althrough
 178          *          its has PROT_NONE permission.
 179          */
 180         if (!mlock)
 181                 gup_flags |= GUP_FLAGS_IGNORE_VMA_PERMISSIONS;
 182
 183         if (vma->vm_flags & VM_WRITE)
 184                 gup_flags |= GUP_FLAGS_WRITE;
 185
 186         while (nr_pages > 0) {
 187                 int i;
 188
 189                 cond_resched();
 190
 191                 /*
 192                  * get_user_pages makes pages present if we are
 193                  * setting mlock. and this extra reference count will
 194                  * disable migration of this page.  However, page may
 195                  * still be truncated out from under us.
 196                  */
 197                 ret = __get_user_pages(current, mm, addr,
 198                                 min_t(int, nr_pages, ARRAY_SIZE(pages)),
 199                                 gup_flags, pages, NULL);
 200                 /*
 201                  * This can happen for, e.g., VM_NONLINEAR regions before
 202                  * a page has been allocated and mapped at a given offset,
 203                  * or for addresses that map beyond end of a file.
 204                  * We'll mlock the the pages if/when they get faulted in.
 205                  */
 206                 if (ret < 0)
 207                         break;
 208                 if (ret == 0) {
 209                         /*
 210                          * We know the vma is there, so the only time
 211                          * we cannot get a single page should be an
 212                          * error (ret < 0) case.
 213                          */
 214                         WARN_ON(1);
 215                         break;
 216                 }
 217
 218                 lru_add_drain();        /* push cached pages to LRU */
 219
 220                 for (i = 0; i < ret; i++) {
 221                         struct page *page = pages[i];
 222
 223                         lock_page(page);
 224                         /*
 225                          * Because we lock page here and migration is blocked
 226                          * by the elevated reference, we need only check for
 227                          * page truncation (file-cache only).
 228                          */
 229                         if (page->mapping) {
 230                                 if (mlock)
 231                                         mlock_vma_page(page);
 232                                 else
 233                                         munlock_vma_page(page);
 234                         }
 235                         unlock_page(page);
 236                         put_page(page);         /* ref from get_user_pages() */
 237
 238                         /*
 239                          * here we assume that get_user_pages() has given us
 240                          * a list of virtually contiguous pages.
 241                          */
 242                         addr += PAGE_SIZE;      /* for next get_user_pages() */
 243                         nr_pages--;
 244                 }
 245                 ret = 0;
 246         }
 247
 248         return ret;     /* count entire vma as locked_vm */
 249 }
 250
 251 /*
 252  * convert get_user_pages() return value to posix mlock() error
 253  */
 254 static int __mlock_posix_error_return(long retval)
 255 {
 256         if (retval == -EFAULT)
 257                 retval = -ENOMEM;
 258         else if (retval == -ENOMEM)
 259                 retval = -EAGAIN;
 260         return retval;
 261 }
 262
 263 #else /* CONFIG_UNEVICTABLE_LRU */
 264
 265 /*
 266  * Just make pages present if VM_LOCKED.  No-op if unlocking.
 267  */
 268 static long __mlock_vma_pages_range(struct vm_area_struct *vma,
 269                                    unsigned long start, unsigned long end,
 270                                    int mlock)
 271 {
 272         if (mlock && (vma->vm_flags & VM_LOCKED))
 273                 return make_pages_present(start, end);
 274         return 0;
 275 }
 276
 277 static inline int __mlock_posix_error_return(long retval)
 278 {
 279         return 0;
 280 }
 281
 282 #endif /* CONFIG_UNEVICTABLE_LRU */
 283
 284 /**
 285  * mlock_vma_pages_range() - mlock pages in specified vma range.
 286  * @vma - the vma containing the specfied address range
 287  * @start - starting address in @vma to mlock
 288  * @end   - end address [+1] in @vma to mlock
 289  *
 290  * For mmap()/mremap()/expansion of mlocked vma.
 291  *
 292  * return 0 on success for "normal" vmas.
 293  *
 294  * return number of pages [> 0] to be removed from locked_vm on success
 295  * of "special" vmas.
 296  *
 297  * return negative error if vma spanning @start-@range disappears while
 298  * mmap semaphore is dropped.  Unlikely?
 299  */
 300 long mlock_vma_pages_range(struct vm_area_struct *vma,
 301                         unsigned long start, unsigned long end)
 302 {
 303         struct mm_struct *mm = vma->vm_mm;
 304         int nr_pages = (end - start) / PAGE_SIZE;
 305         BUG_ON(!(vma->vm_flags & VM_LOCKED));
 306
 307         /*
 308          * filter unlockable vmas
 309          */
 310         if (vma->vm_flags & (VM_IO | VM_PFNMAP))
 311                 goto no_mlock;
 312
 313         if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
 314                         is_vm_hugetlb_page(vma) ||
 315                         vma == get_gate_vma(current))) {
 316                 long error;
 317                 downgrade_write(&mm->mmap_sem);
 318
 319                 error = __mlock_vma_pages_range(vma, start, end, 1);
 320
 321                 up_read(&mm->mmap_sem);
 322                 /* vma can change or disappear */
 323                 down_write(&mm->mmap_sem);
 324                 vma = find_vma(mm, start);
 325                 /* non-NULL vma must contain @start, but need to check @end */
 326                 if (!vma ||  end > vma->vm_end)
 327                         return -ENOMEM;
 328
 329                 return 0;       /* hide other errors from mmap(), et al */
 330         }
 331
 332         /*
 333          * User mapped kernel pages or huge pages:
 334          * make these pages present to populate the ptes, but
 335          * fall thru' to reset VM_LOCKED--no need to unlock, and
 336          * return nr_pages so these don't get counted against task's
 337          * locked limit.  huge pages are already counted against
 338          * locked vm limit.
 339          */
 340         make_pages_present(start, end);
 341
 342 no_mlock:
 343         vma->vm_flags &= ~VM_LOCKED;    /* and don't come back! */
 344         return nr_pages;                /* error or pages NOT mlocked */
 345 }
 346
 347
 348 /*
 349  * munlock_vma_pages_range() - munlock all pages in the vma range.'
 350  * @vma - vma containing range to be munlock()ed.
 351  * @start - start address in @vma of the range
 352  * @end - end of range in @vma.
 353  *
 354  *  For mremap(), munmap() and exit().
 355  *
 356  * Called with @vma VM_LOCKED.
 357  *
 358  * Returns with VM_LOCKED cleared.  Callers must be prepared to
 359  * deal with this.
 360  *
 361  * We don't save and restore VM_LOCKED here because pages are
 362  * still on lru.  In unmap path, pages might be scanned by reclaim
 363  * and re-mlocked by try_to_{munlock|unmap} before we unmap and
 364  * free them.  This will result in freeing mlocked pages.
 365  */
 366 void munlock_vma_pages_range(struct vm_area_struct *vma,
 367                            unsigned long start, unsigned long end)
 368 {
 369         vma->vm_flags &= ~VM_LOCKED;
 370         __mlock_vma_pages_range(vma, start, end, 0);
 371 }
 372
 373 /*
 374  * mlock_fixup  - handle mlock[all]/munlock[all] requests.
 375  *
 376  * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
 377  * munlock is a no-op.  However, for some special vmas, we go ahead and
 378  * populate the ptes via make_pages_present().
 379  *
 380  * For vmas that pass the filters, merge/split as appropriate.
 381  */
 382 static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
 383         unsigned long start, unsigned long end, unsigned int newflags)
 384 {
 385         struct mm_struct *mm = vma->vm_mm;
 386         pgoff_t pgoff;
 387         int nr_pages;
 388         int ret = 0;
 389         int lock = newflags & VM_LOCKED;
 390
 391         if (newflags == vma->vm_flags ||
 392                         (vma->vm_flags & (VM_IO | VM_PFNMAP)))
 393                 goto out;       /* don't set VM_LOCKED,  don't count */
 394
 395         if ((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
 396                         is_vm_hugetlb_page(vma) ||
 397                         vma == get_gate_vma(current)) {
 398                 if (lock)
 399                         make_pages_present(start, end);
 400                 goto out;       /* don't set VM_LOCKED,  don't count */
 401         }
 402
 403         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 404         *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
 405                           vma->vm_file, pgoff, vma_policy(vma));
 406         if (*prev) {
 407                 vma = *prev;
 408                 goto success;
 409         }
 410
 411         if (start != vma->vm_start) {
 412                 ret = split_vma(mm, vma, start, 1);
 413                 if (ret)
 414                         goto out;
 415         }
 416
 417         if (end != vma->vm_end) {
 418                 ret = split_vma(mm, vma, end, 0);
 419                 if (ret)
 420                         goto out;
 421         }
 422
 423 success:
 424         /*
 425          * Keep track of amount of locked VM.
 426          */
 427         nr_pages = (end - start) >> PAGE_SHIFT;
 428         if (!lock)
 429                 nr_pages = -nr_pages;
 430         mm->locked_vm += nr_pages;
 431
 432         /*
 433          * vm_flags is protected by the mmap_sem held in write mode.
 434          * It's okay if try_to_unmap_one unmaps a page just after we
 435          * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
 436          */
 437         vma->vm_flags = newflags;
 438
 439         if (lock) {
 440                 /*
 441                  * mmap_sem is currently held for write.  Downgrade the write
 442                  * lock to a read lock so that other faults, mmap scans, ...
 443                  * while we fault in all pages.
 444                  */
 445                 downgrade_write(&mm->mmap_sem);
 446
 447                 ret = __mlock_vma_pages_range(vma, start, end, 1);
 448
 449                 /*
 450                  * Need to reacquire mmap sem in write mode, as our callers
 451                  * expect this.  We have no support for atomically upgrading
 452                  * a sem to write, so we need to check for ranges while sem
 453                  * is unlocked.
 454                  */
 455                 up_read(&mm->mmap_sem);
 456                 /* vma can change or disappear */
 457                 down_write(&mm->mmap_sem);
 458                 *prev = find_vma(mm, start);
 459                 /* non-NULL *prev must contain @start, but need to check @end */
 460                 if (!(*prev) || end > (*prev)->vm_end)
 461                         ret = -ENOMEM;
 462                 else if (ret > 0) {
 463                         mm->locked_vm -= ret;
 464                         ret = 0;
 465                 } else
 466                         ret = __mlock_posix_error_return(ret); /* translate if needed */
 467         } else {
 468                 /*
 469                  * TODO:  for unlocking, pages will already be resident, so
 470                  * we don't need to wait for allocations/reclaim/pagein, ...
 471                  * However, unlocking a very large region can still take a
 472                  * while.  Should we downgrade the semaphore for both lock
 473                  * AND unlock ?
 474                  */
 475                 __mlock_vma_pages_range(vma, start, end, 0);
 476         }
 477
 478 out:
 479         *prev = vma;
 480         return ret;
 481 }
 482
 483 static int do_mlock(unsigned long start, size_t len, int on)
 484 {
 485         unsigned long nstart, end, tmp;
 486         struct vm_area_struct * vma, * prev;
 487         int error;
 488
 489         len = PAGE_ALIGN(len);
 490         end = start + len;
 491         if (end < start)
 492                 return -EINVAL;
 493         if (end == start)
 494                 return 0;
 495         vma = find_vma_prev(current->mm, start, &prev);
 496         if (!vma || vma->vm_start > start)
 497                 return -ENOMEM;
 498
 499         if (start > vma->vm_start)
 500                 prev = vma;
 501
 502         for (nstart = start ; ; ) {
 503                 unsigned int newflags;
 504
 505                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 506
 507                 newflags = vma->vm_flags | VM_LOCKED;
 508                 if (!on)
 509                         newflags &= ~VM_LOCKED;
 510
 511                 tmp = vma->vm_end;
 512                 if (tmp > end)
 513                         tmp = end;
 514                 error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
 515                 if (error)
 516                         break;
 517                 nstart = tmp;
 518                 if (nstart < prev->vm_end)
 519                         nstart = prev->vm_end;
 520                 if (nstart >= end)
 521                         break;
 522
 523                 vma = prev->vm_next;
 524                 if (!vma || vma->vm_start != nstart) {
 525                         error = -ENOMEM;
 526                         break;
 527                 }
 528         }
 529         return error;
 530 }
 531
 532 asmlinkage long sys_mlock(unsigned long start, size_t len)
 533 {
 534         unsigned long locked;
 535         unsigned long lock_limit;
 536         int error = -ENOMEM;
 537
 538         if (!can_do_mlock())
 539                 return -EPERM;
 540
 541         lru_add_drain_all();    /* flush pagevec */
 542
 543         down_write(&current->mm->mmap_sem);
 544         len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 545         start &= PAGE_MASK;
 546
 547         locked = len >> PAGE_SHIFT;
 548         locked += current->mm->locked_vm;
 549
 550         lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
 551         lock_limit >>= PAGE_SHIFT;
 552
 553         /* check against resource limits */
 554         if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
 555                 error = do_mlock(start, len, 1);
 556         up_write(&current->mm->mmap_sem);
 557         return error;
 558 }
 559
 560 asmlinkage long sys_munlock(unsigned long start, size_t len)
 561 {
 562         int ret;
 563
 564         down_write(&current->mm->mmap_sem);
 565         len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 566         start &= PAGE_MASK;
 567         ret = do_mlock(start, len, 0);
 568         up_write(&current->mm->mmap_sem);
 569         return ret;
 570 }
 571
 572 static int do_mlockall(int flags)
 573 {
 574         struct vm_area_struct * vma, * prev = NULL;
 575         unsigned int def_flags = 0;
 576
 577         if (flags & MCL_FUTURE)
 578                 def_flags = VM_LOCKED;
 579         current->mm->def_flags = def_flags;
 580         if (flags == MCL_FUTURE)
 581                 goto out;
 582
 583         for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
 584                 unsigned int newflags;
 585
 586                 newflags = vma->vm_flags | VM_LOCKED;
 587                 if (!(flags & MCL_CURRENT))
 588                         newflags &= ~VM_LOCKED;
 589
 590                 /* Ignore errors */
 591                 mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
 592         }
 593 out:
 594         return 0;
 595 }
 596
 597 asmlinkage long sys_mlockall(int flags)
 598 {
 599         unsigned long lock_limit;
 600         int ret = -EINVAL;
 601
 602         if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
 603                 goto out;
 604
 605         ret = -EPERM;
 606         if (!can_do_mlock())
 607                 goto out;
 608
 609         lru_add_drain_all();    /* flush pagevec */
 610
 611         down_write(&current->mm->mmap_sem);
 612
 613         lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
 614         lock_limit >>= PAGE_SHIFT;
 615
 616         ret = -ENOMEM;
 617         if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
 618             capable(CAP_IPC_LOCK))
 619                 ret = do_mlockall(flags);
 620         up_write(&current->mm->mmap_sem);
 621 out:
 622         return ret;
 623 }
 624
 625 asmlinkage long sys_munlockall(void)
 626 {
 627         int ret;
 628
 629         down_write(&current->mm->mmap_sem);
 630         ret = do_mlockall(0);
 631         up_write(&current->mm->mmap_sem);
 632         return ret;
 633 }
 634
 635 /*
 636  * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
 637  * shm segments) get accounted against the user_struct instead.
 638  */
 639 static DEFINE_SPINLOCK(shmlock_user_lock);
 640
 641 int user_shm_lock(size_t size, struct user_struct *user)
 642 {
 643         unsigned long lock_limit, locked;
 644         int allowed = 0;
 645
 646         locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 647         lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
 648         if (lock_limit == RLIM_INFINITY)
 649                 allowed = 1;
 650         lock_limit >>= PAGE_SHIFT;
 651         spin_lock(&shmlock_user_lock);
 652         if (!allowed &&
 653             locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
 654                 goto out;
 655         get_uid(user);
 656         user->locked_shm += locked;
 657         allowed = 1;
 658 out:
 659         spin_unlock(&shmlock_user_lock);
 660         return allowed;
 661 }
 662
 663 void user_shm_unlock(size_t size, struct user_struct *user)
 664 {
 665         spin_lock(&shmlock_user_lock);
 666         user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 667         spin_unlock(&shmlock_user_lock);
 668         free_uid(user);
 669 }
 670
 671 void *alloc_locked_buffer(size_t size)
 672 {
 673         unsigned long rlim, vm, pgsz;
 674         void *buffer = NULL;
 675
 676         pgsz = PAGE_ALIGN(size) >> PAGE_SHIFT;
 677
 678         down_write(&current->mm->mmap_sem);
 679
 680         rlim = current->signal->rlim[RLIMIT_AS].rlim_cur >> PAGE_SHIFT;
 681         vm   = current->mm->total_vm + pgsz;
 682         if (rlim < vm)
 683                 goto out;
 684
 685         rlim = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur >> PAGE_SHIFT;
 686         vm   = current->mm->locked_vm + pgsz;
 687         if (rlim < vm)
 688                 goto out;
 689
 690         buffer = kzalloc(size, GFP_KERNEL);
 691         if (!buffer)
 692                 goto out;
 693
 694         current->mm->total_vm  += pgsz;
 695         current->mm->locked_vm += pgsz;
 696
 697  out:
 698         up_write(&current->mm->mmap_sem);
 699         return buffer;
 700 }
 701
 702 void free_locked_buffer(void *buffer, size_t size)
 703 {
 704         unsigned long pgsz = PAGE_ALIGN(size) >> PAGE_SHIFT;
 705
 706         down_write(&current->mm->mmap_sem);
 707
 708         current->mm->total_vm  -= pgsz;
 709         current->mm->locked_vm -= pgsz;
 710
 711         up_write(&current->mm->mmap_sem);
 712
 713         kfree(buffer);
 714 }