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 vma has PROT_NONE permission.
 177          * munlock: always do munlock although the vma has PROT_NONE
 178          *          permission, or SIGKILL is pending.
 179          */
 180         if (!mlock)
 181                 gup_flags |= GUP_FLAGS_IGNORE_VMA_PERMISSIONS |
 182                              GUP_FLAGS_IGNORE_SIGKILL;
 183
 184         if (vma->vm_flags & VM_WRITE)
 185                 gup_flags |= GUP_FLAGS_WRITE;
 186
 187         while (nr_pages > 0) {
 188                 int i;
 189
 190                 cond_resched();
 191
 192                 /*
 193                  * get_user_pages makes pages present if we are
 194                  * setting mlock. and this extra reference count will
 195                  * disable migration of this page.  However, page may
 196                  * still be truncated out from under us.
 197                  */
 198                 ret = __get_user_pages(current, mm, addr,
 199                                 min_t(int, nr_pages, ARRAY_SIZE(pages)),
 200                                 gup_flags, pages, NULL);
 201                 /*
 202                  * This can happen for, e.g., VM_NONLINEAR regions before
 203                  * a page has been allocated and mapped at a given offset,
 204                  * or for addresses that map beyond end of a file.
 205                  * We'll mlock the the pages if/when they get faulted in.
 206                  */
 207                 if (ret < 0)
 208                         break;
 209                 if (ret == 0) {
 210                         /*
 211                          * We know the vma is there, so the only time
 212                          * we cannot get a single page should be an
 213                          * error (ret < 0) case.
 214                          */
 215                         WARN_ON(1);
 216                         break;
 217                 }
 218
 219                 lru_add_drain();        /* push cached pages to LRU */
 220
 221                 for (i = 0; i < ret; i++) {
 222                         struct page *page = pages[i];
 223
 224                         lock_page(page);
 225                         /*
 226                          * Because we lock page here and migration is blocked
 227                          * by the elevated reference, we need only check for
 228                          * page truncation (file-cache only).
 229                          */
 230                         if (page->mapping) {
 231                                 if (mlock)
 232                                         mlock_vma_page(page);
 233                                 else
 234                                         munlock_vma_page(page);
 235                         }
 236                         unlock_page(page);
 237                         put_page(page);         /* ref from get_user_pages() */
 238
 239                         /*
 240                          * here we assume that get_user_pages() has given us
 241                          * a list of virtually contiguous pages.
 242                          */
 243                         addr += PAGE_SIZE;      /* for next get_user_pages() */
 244                         nr_pages--;
 245                 }
 246                 ret = 0;
 247         }
 248
 249         return ret;     /* count entire vma as locked_vm */
 250 }
 251
 252 /*
 253  * convert get_user_pages() return value to posix mlock() error
 254  */
 255 static int __mlock_posix_error_return(long retval)
 256 {
 257         if (retval == -EFAULT)
 258                 retval = -ENOMEM;
 259         else if (retval == -ENOMEM)
 260                 retval = -EAGAIN;
 261         return retval;
 262 }
 263
 264 #else /* CONFIG_UNEVICTABLE_LRU */
 265
 266 /*
 267  * Just make pages present if VM_LOCKED.  No-op if unlocking.
 268  */
 269 static long __mlock_vma_pages_range(struct vm_area_struct *vma,
 270                                    unsigned long start, unsigned long end,
 271                                    int mlock)
 272 {
 273         if (mlock && (vma->vm_flags & VM_LOCKED))
 274                 return make_pages_present(start, end);
 275         return 0;
 276 }
 277
 278 static inline int __mlock_posix_error_return(long retval)
 279 {
 280         return 0;
 281 }
 282
 283 #endif /* CONFIG_UNEVICTABLE_LRU */
 284
 285 /**
 286  * mlock_vma_pages_range() - mlock pages in specified vma range.
 287  * @vma - the vma containing the specfied address range
 288  * @start - starting address in @vma to mlock
 289  * @end   - end address [+1] in @vma to mlock
 290  *
 291  * For mmap()/mremap()/expansion of mlocked vma.
 292  *
 293  * return 0 on success for "normal" vmas.
 294  *
 295  * return number of pages [> 0] to be removed from locked_vm on success
 296  * of "special" vmas.
 297  */
 298 long mlock_vma_pages_range(struct vm_area_struct *vma,
 299                         unsigned long start, unsigned long end)
 300 {
 301         int nr_pages = (end - start) / PAGE_SIZE;
 302         BUG_ON(!(vma->vm_flags & VM_LOCKED));
 303
 304         /*
 305          * filter unlockable vmas
 306          */
 307         if (vma->vm_flags & (VM_IO | VM_PFNMAP))
 308                 goto no_mlock;
 309
 310         if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
 311                         is_vm_hugetlb_page(vma) ||
 312                         vma == get_gate_vma(current))) {
 313
 314                 __mlock_vma_pages_range(vma, start, end, 1);
 315
 316                 /* Hide errors from mmap() and other callers */
 317                 return 0;
 318         }
 319
 320         /*
 321          * User mapped kernel pages or huge pages:
 322          * make these pages present to populate the ptes, but
 323          * fall thru' to reset VM_LOCKED--no need to unlock, and
 324          * return nr_pages so these don't get counted against task's
 325          * locked limit.  huge pages are already counted against
 326          * locked vm limit.
 327          */
 328         make_pages_present(start, end);
 329
 330 no_mlock:
 331         vma->vm_flags &= ~VM_LOCKED;    /* and don't come back! */
 332         return nr_pages;                /* error or pages NOT mlocked */
 333 }
 334
 335
 336 /*
 337  * munlock_vma_pages_range() - munlock all pages in the vma range.'
 338  * @vma - vma containing range to be munlock()ed.
 339  * @start - start address in @vma of the range
 340  * @end - end of range in @vma.
 341  *
 342  *  For mremap(), munmap() and exit().
 343  *
 344  * Called with @vma VM_LOCKED.
 345  *
 346  * Returns with VM_LOCKED cleared.  Callers must be prepared to
 347  * deal with this.
 348  *
 349  * We don't save and restore VM_LOCKED here because pages are
 350  * still on lru.  In unmap path, pages might be scanned by reclaim
 351  * and re-mlocked by try_to_{munlock|unmap} before we unmap and
 352  * free them.  This will result in freeing mlocked pages.
 353  */
 354 void munlock_vma_pages_range(struct vm_area_struct *vma,
 355                            unsigned long start, unsigned long end)
 356 {
 357         vma->vm_flags &= ~VM_LOCKED;
 358         __mlock_vma_pages_range(vma, start, end, 0);
 359 }
 360
 361 /*
 362  * mlock_fixup  - handle mlock[all]/munlock[all] requests.
 363  *
 364  * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
 365  * munlock is a no-op.  However, for some special vmas, we go ahead and
 366  * populate the ptes via make_pages_present().
 367  *
 368  * For vmas that pass the filters, merge/split as appropriate.
 369  */
 370 static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
 371         unsigned long start, unsigned long end, unsigned int newflags)
 372 {
 373         struct mm_struct *mm = vma->vm_mm;
 374         pgoff_t pgoff;
 375         int nr_pages;
 376         int ret = 0;
 377         int lock = newflags & VM_LOCKED;
 378
 379         if (newflags == vma->vm_flags ||
 380                         (vma->vm_flags & (VM_IO | VM_PFNMAP)))
 381                 goto out;       /* don't set VM_LOCKED,  don't count */
 382
 383         if ((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
 384                         is_vm_hugetlb_page(vma) ||
 385                         vma == get_gate_vma(current)) {
 386                 if (lock)
 387                         make_pages_present(start, end);
 388                 goto out;       /* don't set VM_LOCKED,  don't count */
 389         }
 390
 391         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 392         *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
 393                           vma->vm_file, pgoff, vma_policy(vma));
 394         if (*prev) {
 395                 vma = *prev;
 396                 goto success;
 397         }
 398
 399         if (start != vma->vm_start) {
 400                 ret = split_vma(mm, vma, start, 1);
 401                 if (ret)
 402                         goto out;
 403         }
 404
 405         if (end != vma->vm_end) {
 406                 ret = split_vma(mm, vma, end, 0);
 407                 if (ret)
 408                         goto out;
 409         }
 410
 411 success:
 412         /*
 413          * Keep track of amount of locked VM.
 414          */
 415         nr_pages = (end - start) >> PAGE_SHIFT;
 416         if (!lock)
 417                 nr_pages = -nr_pages;
 418         mm->locked_vm += nr_pages;
 419
 420         /*
 421          * vm_flags is protected by the mmap_sem held in write mode.
 422          * It's okay if try_to_unmap_one unmaps a page just after we
 423          * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
 424          */
 425         vma->vm_flags = newflags;
 426
 427         if (lock) {
 428                 ret = __mlock_vma_pages_range(vma, start, end, 1);
 429
 430                 if (ret > 0) {
 431                         mm->locked_vm -= ret;
 432                         ret = 0;
 433                 } else
 434                         ret = __mlock_posix_error_return(ret); /* translate if needed */
 435         } else {
 436                 __mlock_vma_pages_range(vma, start, end, 0);
 437         }
 438
 439 out:
 440         *prev = vma;
 441         return ret;
 442 }
 443
 444 static int do_mlock(unsigned long start, size_t len, int on)
 445 {
 446         unsigned long nstart, end, tmp;
 447         struct vm_area_struct * vma, * prev;
 448         int error;
 449
 450         len = PAGE_ALIGN(len);
 451         end = start + len;
 452         if (end < start)
 453                 return -EINVAL;
 454         if (end == start)
 455                 return 0;
 456         vma = find_vma_prev(current->mm, start, &prev);
 457         if (!vma || vma->vm_start > start)
 458                 return -ENOMEM;
 459
 460         if (start > vma->vm_start)
 461                 prev = vma;
 462
 463         for (nstart = start ; ; ) {
 464                 unsigned int newflags;
 465
 466                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 467
 468                 newflags = vma->vm_flags | VM_LOCKED;
 469                 if (!on)
 470                         newflags &= ~VM_LOCKED;
 471
 472                 tmp = vma->vm_end;
 473                 if (tmp > end)
 474                         tmp = end;
 475                 error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
 476                 if (error)
 477                         break;
 478                 nstart = tmp;
 479                 if (nstart < prev->vm_end)
 480                         nstart = prev->vm_end;
 481                 if (nstart >= end)
 482                         break;
 483
 484                 vma = prev->vm_next;
 485                 if (!vma || vma->vm_start != nstart) {
 486                         error = -ENOMEM;
 487                         break;
 488                 }
 489         }
 490         return error;
 491 }
 492
 493 SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
 494 {
 495         unsigned long locked;
 496         unsigned long lock_limit;
 497         int error = -ENOMEM;
 498
 499         if (!can_do_mlock())
 500                 return -EPERM;
 501
 502         lru_add_drain_all();    /* flush pagevec */
 503
 504         down_write(&current->mm->mmap_sem);
 505         len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 506         start &= PAGE_MASK;
 507
 508         locked = len >> PAGE_SHIFT;
 509         locked += current->mm->locked_vm;
 510
 511         lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
 512         lock_limit >>= PAGE_SHIFT;
 513
 514         /* check against resource limits */
 515         if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
 516                 error = do_mlock(start, len, 1);
 517         up_write(&current->mm->mmap_sem);
 518         return error;
 519 }
 520
 521 SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
 522 {
 523         int ret;
 524
 525         down_write(&current->mm->mmap_sem);
 526         len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 527         start &= PAGE_MASK;
 528         ret = do_mlock(start, len, 0);
 529         up_write(&current->mm->mmap_sem);
 530         return ret;
 531 }
 532
 533 static int do_mlockall(int flags)
 534 {
 535         struct vm_area_struct * vma, * prev = NULL;
 536         unsigned int def_flags = 0;
 537
 538         if (flags & MCL_FUTURE)
 539                 def_flags = VM_LOCKED;
 540         current->mm->def_flags = def_flags;
 541         if (flags == MCL_FUTURE)
 542                 goto out;
 543
 544         for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
 545                 unsigned int newflags;
 546
 547                 newflags = vma->vm_flags | VM_LOCKED;
 548                 if (!(flags & MCL_CURRENT))
 549                         newflags &= ~VM_LOCKED;
 550
 551                 /* Ignore errors */
 552                 mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
 553         }
 554 out:
 555         return 0;
 556 }
 557
 558 SYSCALL_DEFINE1(mlockall, int, flags)
 559 {
 560         unsigned long lock_limit;
 561         int ret = -EINVAL;
 562
 563         if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
 564                 goto out;
 565
 566         ret = -EPERM;
 567         if (!can_do_mlock())
 568                 goto out;
 569
 570         lru_add_drain_all();    /* flush pagevec */
 571
 572         down_write(&current->mm->mmap_sem);
 573
 574         lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
 575         lock_limit >>= PAGE_SHIFT;
 576
 577         ret = -ENOMEM;
 578         if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
 579             capable(CAP_IPC_LOCK))
 580                 ret = do_mlockall(flags);
 581         up_write(&current->mm->mmap_sem);
 582 out:
 583         return ret;
 584 }
 585
 586 SYSCALL_DEFINE0(munlockall)
 587 {
 588         int ret;
 589
 590         down_write(&current->mm->mmap_sem);
 591         ret = do_mlockall(0);
 592         up_write(&current->mm->mmap_sem);
 593         return ret;
 594 }
 595
 596 /*
 597  * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
 598  * shm segments) get accounted against the user_struct instead.
 599  */
 600 static DEFINE_SPINLOCK(shmlock_user_lock);
 601
 602 int user_shm_lock(size_t size, struct user_struct *user)
 603 {
 604         unsigned long lock_limit, locked;
 605         int allowed = 0;
 606
 607         locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 608         lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
 609         if (lock_limit == RLIM_INFINITY)
 610                 allowed = 1;
 611         lock_limit >>= PAGE_SHIFT;
 612         spin_lock(&shmlock_user_lock);
 613         if (!allowed &&
 614             locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
 615                 goto out;
 616         get_uid(user);
 617         user->locked_shm += locked;
 618         allowed = 1;
 619 out:
 620         spin_unlock(&shmlock_user_lock);
 621         return allowed;
 622 }
 623
 624 void user_shm_unlock(size_t size, struct user_struct *user)
 625 {
 626         spin_lock(&shmlock_user_lock);
 627         user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 628         spin_unlock(&shmlock_user_lock);
 629         free_uid(user);
 630 }
 631
 632 void *alloc_locked_buffer(size_t size)
 633 {
 634         unsigned long rlim, vm, pgsz;
 635         void *buffer = NULL;
 636
 637         pgsz = PAGE_ALIGN(size) >> PAGE_SHIFT;
 638
 639         down_write(&current->mm->mmap_sem);
 640
 641         rlim = current->signal->rlim[RLIMIT_AS].rlim_cur >> PAGE_SHIFT;
 642         vm   = current->mm->total_vm + pgsz;
 643         if (rlim < vm)
 644                 goto out;
 645
 646         rlim = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur >> PAGE_SHIFT;
 647         vm   = current->mm->locked_vm + pgsz;
 648         if (rlim < vm)
 649                 goto out;
 650
 651         buffer = kzalloc(size, GFP_KERNEL);
 652         if (!buffer)
 653                 goto out;
 654
 655         current->mm->total_vm  += pgsz;
 656         current->mm->locked_vm += pgsz;
 657
 658  out:
 659         up_write(&current->mm->mmap_sem);
 660         return buffer;
 661 }
 662
 663 void release_locked_buffer(void *buffer, size_t size)
 664 {
 665         unsigned long pgsz = PAGE_ALIGN(size) >> PAGE_SHIFT;
 666
 667         down_write(&current->mm->mmap_sem);
 668
 669         current->mm->total_vm  -= pgsz;
 670         current->mm->locked_vm -= pgsz;
 671
 672         up_write(&current->mm->mmap_sem);
 673 }
 674
 675 void free_locked_buffer(void *buffer, size_t size)
 676 {
 677         release_locked_buffer(buffer, size);
 678
 679         kfree(buffer);
 680 }