sys/kern/kern_subr.c

   1 /*
   2  * Copyright (c) 1982, 1986, 1991, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  * (c) UNIX System Laboratories, Inc.
   5  * All or some portions of this file are derived from material licensed
   6  * to the University of California by American Telephone and Telegraph
   7  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
   8  * the permission of UNIX System Laboratories, Inc.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  * 3. Neither the name of the University nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  *
  34  *      @(#)kern_subr.c 8.3 (Berkeley) 1/21/94
  35  * $FreeBSD: src/sys/kern/kern_subr.c,v 1.31.2.2 2002/04/21 08:09:37 bde Exp $
  36  */
  37
  38 #include <sys/param.h>
  39 #include <sys/systm.h>
  40 #include <sys/kernel.h>
  41 #include <sys/proc.h>
  42 #include <sys/malloc.h>
  43 #include <sys/lock.h>
  44 #include <sys/resourcevar.h>
  45 #include <sys/sysctl.h>
  46 #include <sys/uio.h>
  47 #include <sys/vnode.h>
  48 #include <sys/thread2.h>
  49 #include <machine/limits.h>
  50
  51 #include <cpu/lwbuf.h>
  52
  53 #include <vm/vm.h>
  54 #include <vm/vm_page.h>
  55 #include <vm/vm_map.h>
  56
  57 SYSCTL_INT(_kern, KERN_IOV_MAX, iov_max, CTLFLAG_RD, NULL, UIO_MAXIOV,
  58         "Maximum number of elements in an I/O vector; sysconf(_SC_IOV_MAX)");
  59
  60 int
  61 copyin_nofault(const void *udaddr, void *kaddr, size_t len)
  62 {
  63         thread_t td = curthread;
  64         int error;
  65
  66         atomic_set_int(&td->td_flags, TDF_NOFAULT);
  67         error = copyin(udaddr, kaddr, len);
  68         atomic_clear_int(&td->td_flags, TDF_NOFAULT);
  69         return error;
  70 }
  71
  72 int
  73 copyout_nofault(const void *kaddr, void *udaddr, size_t len)
  74 {
  75         thread_t td = curthread;
  76         int error;
  77
  78         atomic_set_int(&td->td_flags, TDF_NOFAULT);
  79         error = copyout(kaddr, udaddr, len);
  80         atomic_clear_int(&td->td_flags, TDF_NOFAULT);
  81         return error;
  82 }
  83
  84 /*
  85  * UIO_READ:    copy the kernelspace cp to the user or kernelspace UIO
  86  * UIO_WRITE:   copy the user or kernelspace UIO to the kernelspace cp
  87  *
  88  * For userspace UIO's, uio_td must be the current thread.
  89  *
  90  * The syscall interface is responsible for limiting the length to
  91  * ssize_t for things like read() or write() which return the bytes
  92  * read or written as ssize_t.  These functions work with unsigned
  93  * lengths.
  94  */
  95 int
  96 uiomove(caddr_t cp, size_t n, struct uio *uio)
  97 {
  98         thread_t td = curthread;
  99         struct iovec *iov;
 100         size_t cnt;
 101         size_t tot;
 102         int error = 0;
 103         int save = 0;
 104
 105         KASSERT(uio->uio_rw == UIO_READ || uio->uio_rw == UIO_WRITE,
 106             ("uiomove: mode"));
 107         KASSERT(uio->uio_segflg != UIO_USERSPACE || uio->uio_td == td,
 108             ("uiomove proc"));
 109
 110         crit_enter();
 111         save = td->td_flags & TDF_DEADLKTREAT;
 112         td->td_flags |= TDF_DEADLKTREAT;
 113         crit_exit();
 114
 115         tot = 0;
 116
 117         while (n > 0 && uio->uio_resid) {
 118                 iov = uio->uio_iov;
 119                 cnt = iov->iov_len;
 120                 if (cnt == 0) {
 121                         uio->uio_iov++;
 122                         uio->uio_iovcnt--;
 123                         continue;
 124                 }
 125                 if (cnt > n)
 126                         cnt = n;
 127                 tot += cnt;
 128
 129                 switch (uio->uio_segflg) {
 130                 case UIO_USERSPACE:
 131                         if (tot > 1024*1024)
 132                                 lwkt_user_yield();
 133                         if (uio->uio_rw == UIO_READ)
 134                                 error = copyout(cp, iov->iov_base, cnt);
 135                         else
 136                                 error = copyin(iov->iov_base, cp, cnt);
 137                         break;
 138                 case UIO_SYSSPACE:
 139                         if (uio->uio_rw == UIO_READ)
 140                                 bcopy(cp, iov->iov_base, cnt);
 141                         else
 142                                 bcopy(iov->iov_base, cp, cnt);
 143                         break;
 144                 case UIO_NOCOPY:
 145                         break;
 146                 }
 147
 148                 if (error)
 149                         break;
 150                 iov->iov_base = (char *)iov->iov_base + cnt;
 151                 iov->iov_len -= cnt;
 152                 uio->uio_resid -= cnt;
 153                 uio->uio_offset += cnt;
 154                 cp += cnt;
 155                 n -= cnt;
 156         }
 157         crit_enter();
 158         td->td_flags = (td->td_flags & ~TDF_DEADLKTREAT) | save;
 159         crit_exit();
 160
 161         return (error);
 162 }
 163
 164 /*
 165  * This is the same as uiomove() except (cp, n) is within the bounds of
 166  * the passed, locked buffer.  Under certain circumstances a VM fault
 167  * occuring with a locked buffer held can result in a deadlock or an
 168  * attempt to recursively lock the buffer.
 169  *
 170  * This procedure deals with these cases.
 171  *
 172  * If the buffer represents a regular file, is B_CACHE, but the last VM page
 173  * is not fully valid we fix-up the last VM page.  This should handle the
 174  * recursive lock issue.
 175  *
 176  * Deadlocks are another issue.  We are holding the vp and the bp locked
 177  * and could deadlock against a different vp and/or bp if another thread is
 178  * trying to access us while we accessing it.  The only solution here is
 179  * to release the bp and vnode lock and do the uio to/from a system buffer,
 180  * then regain the locks and copyback (if applicable).  XXX TODO.
 181  */
 182 int
 183 uiomovebp(struct buf *bp, caddr_t cp, size_t n, struct uio *uio)
 184 {
 185         int count;
 186         vm_page_t m;
 187
 188         if (bp->b_vp && bp->b_vp->v_type == VREG &&
 189             (bp->b_flags & B_CACHE) &&
 190             (count = bp->b_xio.xio_npages) != 0 &&
 191             (m = bp->b_xio.xio_pages[count-1])->valid != VM_PAGE_BITS_ALL) {
 192                 vm_page_zero_invalid(m, TRUE);
 193         }
 194         return (uiomove(cp, n, uio));
 195 }
 196
 197 /*
 198  * uiomove() but fail for non-trivial VM faults, even if the VM fault is
 199  * valid.  Returns EFAULT if a VM fault occurred via the copyin/copyout
 200  * onfault code.
 201  *
 202  * This allows callers to hold e.g. a busy VM page, or a busy VM object,
 203  * or a locked vnode through the call and then fall-back to safer code
 204  * if we fail.
 205  */
 206 int
 207 uiomove_nofault(caddr_t cp, size_t n, struct uio *uio)
 208 {
 209         thread_t td = curthread;
 210         int error;
 211
 212         atomic_set_int(&td->td_flags, TDF_NOFAULT);
 213         error = uiomove(cp, n, uio);
 214         atomic_clear_int(&td->td_flags, TDF_NOFAULT);
 215         return error;
 216 }
 217
 218 /*
 219  * Like uiomove() but copies zero-fill.  Only allowed for UIO_READ,
 220  * for obvious reasons.
 221  */
 222 int
 223 uiomovez(size_t n, struct uio *uio)
 224 {
 225         struct iovec *iov;
 226         size_t cnt;
 227         int error = 0;
 228
 229         KASSERT(uio->uio_rw == UIO_READ, ("uiomovez: mode"));
 230         KASSERT(uio->uio_segflg != UIO_USERSPACE || uio->uio_td == curthread,
 231                 ("uiomove proc"));
 232
 233         while (n > 0 && uio->uio_resid) {
 234                 iov = uio->uio_iov;
 235                 cnt = iov->iov_len;
 236                 if (cnt == 0) {
 237                         uio->uio_iov++;
 238                         uio->uio_iovcnt--;
 239                         continue;
 240                 }
 241                 if (cnt > n)
 242                         cnt = n;
 243
 244                 switch (uio->uio_segflg) {
 245                 case UIO_USERSPACE:
 246                         error = copyout(ZeroPage, iov->iov_base, cnt);
 247                         break;
 248                 case UIO_SYSSPACE:
 249                         bzero(iov->iov_base, cnt);
 250                         break;
 251                 case UIO_NOCOPY:
 252                         break;
 253                 }
 254
 255                 if (error)
 256                         break;
 257                 iov->iov_base = (char *)iov->iov_base + cnt;
 258                 iov->iov_len -= cnt;
 259                 uio->uio_resid -= cnt;
 260                 uio->uio_offset += cnt;
 261                 n -= cnt;
 262         }
 263         return (error);
 264 }
 265
 266 /*
 267  * Wrapper for uiomove() that validates the arguments against a known-good
 268  * kernel buffer.  This function automatically indexes the buffer by
 269  * uio_offset and handles all range checking.
 270  */
 271 int
 272 uiomove_frombuf(void *buf, size_t buflen, struct uio *uio)
 273 {
 274         size_t offset;
 275
 276         offset = (size_t)uio->uio_offset;
 277         if ((off_t)offset != uio->uio_offset)
 278                 return (EINVAL);
 279         if (buflen == 0 || offset >= buflen)
 280                 return (0);
 281         return (uiomove((char *)buf + offset, buflen - offset, uio));
 282 }
 283
 284 /*
 285  * Give next character to user as result of read.
 286  */
 287 int
 288 ureadc(int c, struct uio *uio)
 289 {
 290         struct iovec *iov;
 291         char *iov_base;
 292
 293 again:
 294         if (uio->uio_iovcnt == 0 || uio->uio_resid == 0)
 295                 panic("ureadc");
 296         iov = uio->uio_iov;
 297         if (iov->iov_len == 0) {
 298                 uio->uio_iovcnt--;
 299                 uio->uio_iov++;
 300                 goto again;
 301         }
 302
 303         switch (uio->uio_segflg) {
 304         case UIO_USERSPACE:
 305                 if (subyte(iov->iov_base, c) < 0)
 306                         return (EFAULT);
 307                 break;
 308         case UIO_SYSSPACE:
 309                 iov_base = iov->iov_base;
 310                 *iov_base = c;
 311                 iov->iov_base = iov_base;
 312                 break;
 313         case UIO_NOCOPY:
 314                 break;
 315         }
 316
 317         iov->iov_base = (char *)iov->iov_base + 1;
 318         iov->iov_len--;
 319         uio->uio_resid--;
 320         uio->uio_offset++;
 321         return (0);
 322 }
 323
 324 /*
 325  * General routine to allocate a hash table.  Make the hash table size a
 326  * power of 2 greater or equal to the number of elements requested, and
 327  * store the masking value in *hashmask.
 328  */
 329 void *
 330 hashinit(int elements, struct malloc_type *type, u_long *hashmask)
 331 {
 332         long hashsize;
 333         LIST_HEAD(generic, generic) *hashtbl;
 334         int i;
 335
 336         if (elements <= 0)
 337                 panic("hashinit: bad elements");
 338         for (hashsize = 2; hashsize < elements; hashsize <<= 1)
 339                 continue;
 340         hashtbl = kmalloc((u_long)hashsize * sizeof(*hashtbl), type, M_WAITOK);
 341         for (i = 0; i < hashsize; i++)
 342                 LIST_INIT(&hashtbl[i]);
 343         *hashmask = hashsize - 1;
 344         return (hashtbl);
 345 }
 346
 347 void
 348 hashdestroy(void *vhashtbl, struct malloc_type *type, u_long hashmask)
 349 {
 350         LIST_HEAD(generic, generic) *hashtbl, *hp;
 351
 352         hashtbl = vhashtbl;
 353         for (hp = hashtbl; hp <= &hashtbl[hashmask]; hp++)
 354                 KASSERT(LIST_EMPTY(hp), ("%s: hash not empty", __func__));
 355         kfree(hashtbl, type);
 356 }
 357
 358 /*
 359  * This is a newer version which allocates a hash table of structures.
 360  *
 361  * The returned array will be zero'd.  The caller is responsible for
 362  * initializing the structures.
 363  */
 364 void *
 365 hashinit_ext(int elements, size_t size, struct malloc_type *type,
 366              u_long *hashmask)
 367 {
 368         long hashsize;
 369         void *hashtbl;
 370
 371         if (elements <= 0)
 372                 panic("hashinit: bad elements");
 373         for (hashsize = 2; hashsize < elements; hashsize <<= 1)
 374                 continue;
 375         hashtbl = kmalloc((size_t)hashsize * size, type, M_WAITOK | M_ZERO);
 376         *hashmask = hashsize - 1;
 377         return (hashtbl);
 378 }
 379
 380 static int primes[] = { 1, 13, 31, 61, 127, 251, 509, 761, 1021, 1531, 2039,
 381                         2557, 3067, 3583, 4093, 4603, 5119, 5623, 6143, 6653,
 382                         7159, 7673, 8191, 12281, 16381, 24571, 32749 };
 383 #define NPRIMES NELEM(primes)
 384
 385 /*
 386  * General routine to allocate a prime number sized hash table.
 387  */
 388 void *
 389 phashinit(int elements, struct malloc_type *type, u_long *nentries)
 390 {
 391         long hashsize;
 392         LIST_HEAD(generic, generic) *hashtbl;
 393         int i;
 394
 395         if (elements <= 0)
 396                 panic("phashinit: bad elements");
 397         for (i = 1, hashsize = primes[1]; hashsize <= elements;) {
 398                 i++;
 399                 if (i == NPRIMES)
 400                         break;
 401                 hashsize = primes[i];
 402         }
 403         hashsize = primes[i - 1];
 404         hashtbl = kmalloc((u_long)hashsize * sizeof(*hashtbl), type, M_WAITOK);
 405         for (i = 0; i < hashsize; i++)
 406                 LIST_INIT(&hashtbl[i]);
 407         *nentries = hashsize;
 408         return (hashtbl);
 409 }
 410
 411 /*
 412  * This is a newer version which allocates a hash table of structures
 413  * in a prime-number size.
 414  *
 415  * The returned array will be zero'd.  The caller is responsible for
 416  * initializing the structures.
 417  */
 418 void *
 419 phashinit_ext(int elements, size_t size, struct malloc_type *type,
 420               u_long *nentries)
 421 {
 422         long hashsize;
 423         void *hashtbl;
 424         int i;
 425
 426         if (elements <= 0)
 427                 panic("phashinit: bad elements");
 428         for (i = 1, hashsize = primes[1]; hashsize <= elements;) {
 429                 i++;
 430                 if (i == NPRIMES)
 431                         break;
 432                 hashsize = primes[i];
 433         }
 434         hashsize = primes[i - 1];
 435         hashtbl = kmalloc((size_t)hashsize * size, type, M_WAITOK | M_ZERO);
 436         *nentries = hashsize;
 437         return (hashtbl);
 438 }
 439
 440 /*
 441  * Copyin an iovec.  If the iovec array fits, use the preallocated small
 442  * iovec structure.  If it is too big, dynamically allocate an iovec array
 443  * of sufficient size.
 444  *
 445  * MPSAFE
 446  */
 447 int
 448 iovec_copyin(struct iovec *uiov, struct iovec **kiov, struct iovec *siov,
 449              size_t iov_cnt, size_t *iov_len)
 450 {
 451         struct iovec *iovp;
 452         int error, i;
 453         size_t len;
 454
 455         if (iov_cnt > UIO_MAXIOV)
 456                 return EMSGSIZE;
 457         if (iov_cnt > UIO_SMALLIOV) {
 458                 *kiov = kmalloc(sizeof(struct iovec) * iov_cnt, M_IOV,
 459                                 M_WAITOK);
 460         } else {
 461                 *kiov = siov;
 462         }
 463         error = copyin(uiov, *kiov, iov_cnt * sizeof(struct iovec));
 464         if (error == 0) {
 465                 *iov_len = 0;
 466                 for (i = 0, iovp = *kiov; i < iov_cnt; i++, iovp++) {
 467                         /*
 468                          * Check for both *iov_len overflows and out of
 469                          * range iovp->iov_len's.  We limit to the
 470                          * capabilities of signed integers.
 471                          *
 472                          * GCC4 - overflow check opt requires assign/test.
 473                          */
 474                         len = *iov_len + iovp->iov_len;
 475                         if (len < *iov_len)
 476                                 error = EINVAL;
 477                         *iov_len = len;
 478                 }
 479         }
 480
 481         /*
 482          * From userland disallow iovec's which exceed the sized size
 483          * limit as the system calls return ssize_t.
 484          *
 485          * NOTE: Internal kernel interfaces can handle the unsigned
 486          *       limit.
 487          */
 488         if (error == 0 && (ssize_t)*iov_len < 0)
 489                 error = EINVAL;
 490
 491         if (error)
 492                 iovec_free(kiov, siov);
 493         return (error);
 494 }
 495
 496
 497 /*
 498  * Copyright (c) 2004 Alan L. Cox <alc@cs.rice.edu>
 499  * Copyright (c) 1982, 1986, 1991, 1993
 500  *      The Regents of the University of California.  All rights reserved.
 501  * (c) UNIX System Laboratories, Inc.
 502  * All or some portions of this file are derived from material licensed
 503  * to the University of California by American Telephone and Telegraph
 504  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 505  * the permission of UNIX System Laboratories, Inc.
 506  *
 507  * Redistribution and use in source and binary forms, with or without
 508  * modification, are permitted provided that the following conditions
 509  * are met:
 510  * 1. Redistributions of source code must retain the above copyright
 511  *    notice, this list of conditions and the following disclaimer.
 512  * 2. Redistributions in binary form must reproduce the above copyright
 513  *    notice, this list of conditions and the following disclaimer in the
 514  *    documentation and/or other materials provided with the distribution.
 515  * 3. Neither the name of the University nor the names of its contributors
 516  *    may be used to endorse or promote products derived from this software
 517  *    without specific prior written permission.
 518  *
 519  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 520  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 521  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 522  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 523  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 524  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 525  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 526  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 527  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 528  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 529  * SUCH DAMAGE.
 530  *
 531  * @(#)kern_subr.c      8.3 (Berkeley) 1/21/94
 532  * $FreeBSD: src/sys/i386/i386/uio_machdep.c,v 1.1 2004/03/21 20:28:36 alc Exp $
 533  */
 534
 535 /*
 536  * Implement uiomove(9) from physical memory using lwbuf's to reduce
 537  * the creation and destruction of ephemeral mappings.
 538  */
 539 int
 540 uiomove_fromphys(vm_page_t *ma, vm_offset_t offset, size_t n, struct uio *uio)
 541 {
 542         struct lwbuf lwb_cache;
 543         struct lwbuf *lwb;
 544         struct thread *td = curthread;
 545         struct iovec *iov;
 546         void *cp;
 547         vm_offset_t page_offset;
 548         vm_page_t m;
 549         size_t cnt;
 550         int error = 0;
 551         int save = 0;
 552
 553         KASSERT(uio->uio_rw == UIO_READ || uio->uio_rw == UIO_WRITE,
 554             ("uiomove_fromphys: mode"));
 555         KASSERT(uio->uio_segflg != UIO_USERSPACE || uio->uio_td == curthread,
 556             ("uiomove_fromphys proc"));
 557
 558         crit_enter();
 559         save = td->td_flags & TDF_DEADLKTREAT;
 560         td->td_flags |= TDF_DEADLKTREAT;
 561         crit_exit();
 562
 563         while (n > 0 && uio->uio_resid) {
 564                 iov = uio->uio_iov;
 565                 cnt = iov->iov_len;
 566                 if (cnt == 0) {
 567                         uio->uio_iov++;
 568                         uio->uio_iovcnt--;
 569                         continue;
 570                 }
 571                 if (cnt > n)
 572                         cnt = n;
 573                 page_offset = offset & PAGE_MASK;
 574                 cnt = min(cnt, PAGE_SIZE - page_offset);
 575                 m = ma[offset >> PAGE_SHIFT];
 576                 lwb = lwbuf_alloc(m, &lwb_cache);
 577                 cp = (char *)lwbuf_kva(lwb) + page_offset;
 578
 579                 switch (uio->uio_segflg) {
 580                 case UIO_USERSPACE:
 581                         /*
 582                          * note: removed uioyield (it was the wrong place to
 583                          * put it).
 584                          */
 585                         if (uio->uio_rw == UIO_READ)
 586                                 error = copyout(cp, iov->iov_base, cnt);
 587                         else
 588                                 error = copyin(iov->iov_base, cp, cnt);
 589                         if (error) {
 590                                 lwbuf_free(lwb);
 591                                 goto out;
 592                         }
 593                         break;
 594                 case UIO_SYSSPACE:
 595                         if (uio->uio_rw == UIO_READ)
 596                                 bcopy(cp, iov->iov_base, cnt);
 597                         else
 598                                 bcopy(iov->iov_base, cp, cnt);
 599                         break;
 600                 case UIO_NOCOPY:
 601                         break;
 602                 }
 603                 lwbuf_free(lwb);
 604                 iov->iov_base = (char *)iov->iov_base + cnt;
 605                 iov->iov_len -= cnt;
 606                 uio->uio_resid -= cnt;
 607                 uio->uio_offset += cnt;
 608                 offset += cnt;
 609                 n -= cnt;
 610         }
 611 out:
 612         if (save == 0) {
 613                 crit_enter();
 614                 td->td_flags &= ~TDF_DEADLKTREAT;
 615                 crit_exit();
 616         }
 617         return (error);
 618 }
 619