fs/pipe.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  linux/fs/pipe.c
   4  *
   5  *  Copyright (C) 1991, 1992, 1999  Linus Torvalds
   6  */
   7
   8 #include <linux/mm.h>
   9 #include <linux/file.h>
  10 #include <linux/poll.h>
  11 #include <linux/slab.h>
  12 #include <linux/module.h>
  13 #include <linux/init.h>
  14 #include <linux/fs.h>
  15 #include <linux/log2.h>
  16 #include <linux/mount.h>
  17 #include <linux/pseudo_fs.h>
  18 #include <linux/magic.h>
  19 #include <linux/pipe_fs_i.h>
  20 #include <linux/uio.h>
  21 #include <linux/highmem.h>
  22 #include <linux/pagemap.h>
  23 #include <linux/audit.h>
  24 #include <linux/syscalls.h>
  25 #include <linux/fcntl.h>
  26 #include <linux/memcontrol.h>
  27
  28 #include <linux/uaccess.h>
  29 #include <asm/ioctls.h>
  30
  31 #include "internal.h"
  32
  33 /*
  34  * The max size that a non-root user is allowed to grow the pipe. Can
  35  * be set by root in /proc/sys/fs/pipe-max-size
  36  */
  37 unsigned int pipe_max_size = 1048576;
  38
  39 /* Maximum allocatable pages per user. Hard limit is unset by default, soft
  40  * matches default values.
  41  */
  42 unsigned long pipe_user_pages_hard;
  43 unsigned long pipe_user_pages_soft = PIPE_DEF_BUFFERS * INR_OPEN_CUR;
  44
  45 /*
  46  * We use head and tail indices that aren't masked off, except at the point of
  47  * dereference, but rather they're allowed to wrap naturally.  This means there
  48  * isn't a dead spot in the buffer, but the ring has to be a power of two and
  49  * <= 2^31.
  50  * -- David Howells 2019-09-23.
  51  *
  52  * Reads with count = 0 should always return 0.
  53  * -- Julian Bradfield 1999-06-07.
  54  *
  55  * FIFOs and Pipes now generate SIGIO for both readers and writers.
  56  * -- Jeremy Elson <jelson@circlemud.org> 2001-08-16
  57  *
  58  * pipe_read & write cleanup
  59  * -- Manfred Spraul <manfred@colorfullife.com> 2002-05-09
  60  */
  61
  62 static void pipe_lock_nested(struct pipe_inode_info *pipe, int subclass)
  63 {
  64         if (pipe->files)
  65                 mutex_lock_nested(&pipe->mutex, subclass);
  66 }
  67
  68 void pipe_lock(struct pipe_inode_info *pipe)
  69 {
  70         /*
  71          * pipe_lock() nests non-pipe inode locks (for writing to a file)
  72          */
  73         pipe_lock_nested(pipe, I_MUTEX_PARENT);
  74 }
  75 EXPORT_SYMBOL(pipe_lock);
  76
  77 void pipe_unlock(struct pipe_inode_info *pipe)
  78 {
  79         if (pipe->files)
  80                 mutex_unlock(&pipe->mutex);
  81 }
  82 EXPORT_SYMBOL(pipe_unlock);
  83
  84 static inline void __pipe_lock(struct pipe_inode_info *pipe)
  85 {
  86         mutex_lock_nested(&pipe->mutex, I_MUTEX_PARENT);
  87 }
  88
  89 static inline void __pipe_unlock(struct pipe_inode_info *pipe)
  90 {
  91         mutex_unlock(&pipe->mutex);
  92 }
  93
  94 void pipe_double_lock(struct pipe_inode_info *pipe1,
  95                       struct pipe_inode_info *pipe2)
  96 {
  97         BUG_ON(pipe1 == pipe2);
  98
  99         if (pipe1 < pipe2) {
 100                 pipe_lock_nested(pipe1, I_MUTEX_PARENT);
 101                 pipe_lock_nested(pipe2, I_MUTEX_CHILD);
 102         } else {
 103                 pipe_lock_nested(pipe2, I_MUTEX_PARENT);
 104                 pipe_lock_nested(pipe1, I_MUTEX_CHILD);
 105         }
 106 }
 107
 108 /* Drop the inode semaphore and wait for a pipe event, atomically */
 109 void pipe_wait(struct pipe_inode_info *pipe)
 110 {
 111         DEFINE_WAIT(rdwait);
 112         DEFINE_WAIT(wrwait);
 113
 114         /*
 115          * Pipes are system-local resources, so sleeping on them
 116          * is considered a noninteractive wait:
 117          */
 118         prepare_to_wait(&pipe->rd_wait, &rdwait, TASK_INTERRUPTIBLE);
 119         prepare_to_wait(&pipe->wr_wait, &wrwait, TASK_INTERRUPTIBLE);
 120         pipe_unlock(pipe);
 121         schedule();
 122         finish_wait(&pipe->rd_wait, &rdwait);
 123         finish_wait(&pipe->wr_wait, &wrwait);
 124         pipe_lock(pipe);
 125 }
 126
 127 static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
 128                                   struct pipe_buffer *buf)
 129 {
 130         struct page *page = buf->page;
 131
 132         /*
 133          * If nobody else uses this page, and we don't already have a
 134          * temporary page, let's keep track of it as a one-deep
 135          * allocation cache. (Otherwise just release our reference to it)
 136          */
 137         if (page_count(page) == 1 && !pipe->tmp_page)
 138                 pipe->tmp_page = page;
 139         else
 140                 put_page(page);
 141 }
 142
 143 static int anon_pipe_buf_steal(struct pipe_inode_info *pipe,
 144                                struct pipe_buffer *buf)
 145 {
 146         struct page *page = buf->page;
 147
 148         if (page_count(page) == 1) {
 149                 memcg_kmem_uncharge_page(page, 0);
 150                 __SetPageLocked(page);
 151                 return 0;
 152         }
 153         return 1;
 154 }
 155
 156 /**
 157  * generic_pipe_buf_steal - attempt to take ownership of a &pipe_buffer
 158  * @pipe:       the pipe that the buffer belongs to
 159  * @buf:        the buffer to attempt to steal
 160  *
 161  * Description:
 162  *      This function attempts to steal the &struct page attached to
 163  *      @buf. If successful, this function returns 0 and returns with
 164  *      the page locked. The caller may then reuse the page for whatever
 165  *      he wishes; the typical use is insertion into a different file
 166  *      page cache.
 167  */
 168 int generic_pipe_buf_steal(struct pipe_inode_info *pipe,
 169                            struct pipe_buffer *buf)
 170 {
 171         struct page *page = buf->page;
 172
 173         /*
 174          * A reference of one is golden, that means that the owner of this
 175          * page is the only one holding a reference to it. lock the page
 176          * and return OK.
 177          */
 178         if (page_count(page) == 1) {
 179                 lock_page(page);
 180                 return 0;
 181         }
 182
 183         return 1;
 184 }
 185 EXPORT_SYMBOL(generic_pipe_buf_steal);
 186
 187 /**
 188  * generic_pipe_buf_get - get a reference to a &struct pipe_buffer
 189  * @pipe:       the pipe that the buffer belongs to
 190  * @buf:        the buffer to get a reference to
 191  *
 192  * Description:
 193  *      This function grabs an extra reference to @buf. It's used in
 194  *      in the tee() system call, when we duplicate the buffers in one
 195  *      pipe into another.
 196  */
 197 bool generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
 198 {
 199         return try_get_page(buf->page);
 200 }
 201 EXPORT_SYMBOL(generic_pipe_buf_get);
 202
 203 /**
 204  * generic_pipe_buf_confirm - verify contents of the pipe buffer
 205  * @info:       the pipe that the buffer belongs to
 206  * @buf:        the buffer to confirm
 207  *
 208  * Description:
 209  *      This function does nothing, because the generic pipe code uses
 210  *      pages that are always good when inserted into the pipe.
 211  */
 212 int generic_pipe_buf_confirm(struct pipe_inode_info *info,
 213                              struct pipe_buffer *buf)
 214 {
 215         return 0;
 216 }
 217 EXPORT_SYMBOL(generic_pipe_buf_confirm);
 218
 219 /**
 220  * generic_pipe_buf_release - put a reference to a &struct pipe_buffer
 221  * @pipe:       the pipe that the buffer belongs to
 222  * @buf:        the buffer to put a reference to
 223  *
 224  * Description:
 225  *      This function releases a reference to @buf.
 226  */
 227 void generic_pipe_buf_release(struct pipe_inode_info *pipe,
 228                               struct pipe_buffer *buf)
 229 {
 230         put_page(buf->page);
 231 }
 232 EXPORT_SYMBOL(generic_pipe_buf_release);
 233
 234 /* New data written to a pipe may be appended to a buffer with this type. */
 235 static const struct pipe_buf_operations anon_pipe_buf_ops = {
 236         .confirm = generic_pipe_buf_confirm,
 237         .release = anon_pipe_buf_release,
 238         .steal = anon_pipe_buf_steal,
 239         .get = generic_pipe_buf_get,
 240 };
 241
 242 static const struct pipe_buf_operations anon_pipe_buf_nomerge_ops = {
 243         .confirm = generic_pipe_buf_confirm,
 244         .release = anon_pipe_buf_release,
 245         .steal = anon_pipe_buf_steal,
 246         .get = generic_pipe_buf_get,
 247 };
 248
 249 static const struct pipe_buf_operations packet_pipe_buf_ops = {
 250         .confirm = generic_pipe_buf_confirm,
 251         .release = anon_pipe_buf_release,
 252         .steal = anon_pipe_buf_steal,
 253         .get = generic_pipe_buf_get,
 254 };
 255
 256 /**
 257  * pipe_buf_mark_unmergeable - mark a &struct pipe_buffer as unmergeable
 258  * @buf:        the buffer to mark
 259  *
 260  * Description:
 261  *      This function ensures that no future writes will be merged into the
 262  *      given &struct pipe_buffer. This is necessary when multiple pipe buffers
 263  *      share the same backing page.
 264  */
 265 void pipe_buf_mark_unmergeable(struct pipe_buffer *buf)
 266 {
 267         if (buf->ops == &anon_pipe_buf_ops)
 268                 buf->ops = &anon_pipe_buf_nomerge_ops;
 269 }
 270
 271 static bool pipe_buf_can_merge(struct pipe_buffer *buf)
 272 {
 273         return buf->ops == &anon_pipe_buf_ops;
 274 }
 275
 276 /* Done while waiting without holding the pipe lock - thus the READ_ONCE() */
 277 static inline bool pipe_readable(const struct pipe_inode_info *pipe)
 278 {
 279         unsigned int head = READ_ONCE(pipe->head);
 280         unsigned int tail = READ_ONCE(pipe->tail);
 281         unsigned int writers = READ_ONCE(pipe->writers);
 282
 283         return !pipe_empty(head, tail) || !writers;
 284 }
 285
 286 static ssize_t
 287 pipe_read(struct kiocb *iocb, struct iov_iter *to)
 288 {
 289         size_t total_len = iov_iter_count(to);
 290         struct file *filp = iocb->ki_filp;
 291         struct pipe_inode_info *pipe = filp->private_data;
 292         bool was_full, wake_next_reader = false;
 293         ssize_t ret;
 294
 295         /* Null read succeeds. */
 296         if (unlikely(total_len == 0))
 297                 return 0;
 298
 299         ret = 0;
 300         __pipe_lock(pipe);
 301
 302         /*
 303          * We only wake up writers if the pipe was full when we started
 304          * reading in order to avoid unnecessary wakeups.
 305          *
 306          * But when we do wake up writers, we do so using a sync wakeup
 307          * (WF_SYNC), because we want them to get going and generate more
 308          * data for us.
 309          */
 310         was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage);
 311         for (;;) {
 312                 unsigned int head = pipe->head;
 313                 unsigned int tail = pipe->tail;
 314                 unsigned int mask = pipe->ring_size - 1;
 315
 316                 if (!pipe_empty(head, tail)) {
 317                         struct pipe_buffer *buf = &pipe->bufs[tail & mask];
 318                         size_t chars = buf->len;
 319                         size_t written;
 320                         int error;
 321
 322                         if (chars > total_len)
 323                                 chars = total_len;
 324
 325                         error = pipe_buf_confirm(pipe, buf);
 326                         if (error) {
 327                                 if (!ret)
 328                                         ret = error;
 329                                 break;
 330                         }
 331
 332                         written = copy_page_to_iter(buf->page, buf->offset, chars, to);
 333                         if (unlikely(written < chars)) {
 334                                 if (!ret)
 335                                         ret = -EFAULT;
 336                                 break;
 337                         }
 338                         ret += chars;
 339                         buf->offset += chars;
 340                         buf->len -= chars;
 341
 342                         /* Was it a packet buffer? Clean up and exit */
 343                         if (buf->flags & PIPE_BUF_FLAG_PACKET) {
 344                                 total_len = chars;
 345                                 buf->len = 0;
 346                         }
 347
 348                         if (!buf->len) {
 349                                 pipe_buf_release(pipe, buf);
 350                                 spin_lock_irq(&pipe->rd_wait.lock);
 351                                 tail++;
 352                                 pipe->tail = tail;
 353                                 spin_unlock_irq(&pipe->rd_wait.lock);
 354                         }
 355                         total_len -= chars;
 356                         if (!total_len)
 357                                 break;  /* common path: read succeeded */
 358                         if (!pipe_empty(head, tail))    /* More to do? */
 359                                 continue;
 360                 }
 361
 362                 if (!pipe->writers)
 363                         break;
 364                 if (ret)
 365                         break;
 366                 if (filp->f_flags & O_NONBLOCK) {
 367                         ret = -EAGAIN;
 368                         break;
 369                 }
 370                 __pipe_unlock(pipe);
 371
 372                 /*
 373                  * We only get here if we didn't actually read anything.
 374                  *
 375                  * However, we could have seen (and removed) a zero-sized
 376                  * pipe buffer, and might have made space in the buffers
 377                  * that way.
 378                  *
 379                  * You can't make zero-sized pipe buffers by doing an empty
 380                  * write (not even in packet mode), but they can happen if
 381                  * the writer gets an EFAULT when trying to fill a buffer
 382                  * that already got allocated and inserted in the buffer
 383                  * array.
 384                  *
 385                  * So we still need to wake up any pending writers in the
 386                  * _very_ unlikely case that the pipe was full, but we got
 387                  * no data.
 388                  */
 389                 if (unlikely(was_full)) {
 390                         wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);
 391                         kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
 392                 }
 393
 394                 /*
 395                  * But because we didn't read anything, at this point we can
 396                  * just return directly with -ERESTARTSYS if we're interrupted,
 397                  * since we've done any required wakeups and there's no need
 398                  * to mark anything accessed. And we've dropped the lock.
 399                  */
 400                 if (wait_event_interruptible_exclusive(pipe->rd_wait, pipe_readable(pipe)) < 0)
 401                         return -ERESTARTSYS;
 402
 403                 __pipe_lock(pipe);
 404                 was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage);
 405                 wake_next_reader = true;
 406         }
 407         if (pipe_empty(pipe->head, pipe->tail))
 408                 wake_next_reader = false;
 409         __pipe_unlock(pipe);
 410
 411         if (was_full) {
 412                 wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);
 413                 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
 414         }
 415         if (wake_next_reader)
 416                 wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
 417         if (ret > 0)
 418                 file_accessed(filp);
 419         return ret;
 420 }
 421
 422 static inline int is_packetized(struct file *file)
 423 {
 424         return (file->f_flags & O_DIRECT) != 0;
 425 }
 426
 427 /* Done while waiting without holding the pipe lock - thus the READ_ONCE() */
 428 static inline bool pipe_writable(const struct pipe_inode_info *pipe)
 429 {
 430         unsigned int head = READ_ONCE(pipe->head);
 431         unsigned int tail = READ_ONCE(pipe->tail);
 432         unsigned int max_usage = READ_ONCE(pipe->max_usage);
 433
 434         return !pipe_full(head, tail, max_usage) ||
 435                 !READ_ONCE(pipe->readers);
 436 }
 437
 438 static ssize_t
 439 pipe_write(struct kiocb *iocb, struct iov_iter *from)
 440 {
 441         struct file *filp = iocb->ki_filp;
 442         struct pipe_inode_info *pipe = filp->private_data;
 443         unsigned int head;
 444         ssize_t ret = 0;
 445         size_t total_len = iov_iter_count(from);
 446         ssize_t chars;
 447         bool was_empty = false;
 448         bool wake_next_writer = false;
 449
 450         /* Null write succeeds. */
 451         if (unlikely(total_len == 0))
 452                 return 0;
 453
 454         __pipe_lock(pipe);
 455
 456         if (!pipe->readers) {
 457                 send_sig(SIGPIPE, current, 0);
 458                 ret = -EPIPE;
 459                 goto out;
 460         }
 461
 462         /*
 463          * Only wake up if the pipe started out empty, since
 464          * otherwise there should be no readers waiting.
 465          *
 466          * If it wasn't empty we try to merge new data into
 467          * the last buffer.
 468          *
 469          * That naturally merges small writes, but it also
 470          * page-aligs the rest of the writes for large writes
 471          * spanning multiple pages.
 472          */
 473         head = pipe->head;
 474         was_empty = pipe_empty(head, pipe->tail);
 475         chars = total_len & (PAGE_SIZE-1);
 476         if (chars && !was_empty) {
 477                 unsigned int mask = pipe->ring_size - 1;
 478                 struct pipe_buffer *buf = &pipe->bufs[(head - 1) & mask];
 479                 int offset = buf->offset + buf->len;
 480
 481                 if (pipe_buf_can_merge(buf) && offset + chars <= PAGE_SIZE) {
 482                         ret = pipe_buf_confirm(pipe, buf);
 483                         if (ret)
 484                                 goto out;
 485
 486                         ret = copy_page_from_iter(buf->page, offset, chars, from);
 487                         if (unlikely(ret < chars)) {
 488                                 ret = -EFAULT;
 489                                 goto out;
 490                         }
 491
 492                         buf->len += ret;
 493                         if (!iov_iter_count(from))
 494                                 goto out;
 495                 }
 496         }
 497
 498         for (;;) {
 499                 if (!pipe->readers) {
 500                         send_sig(SIGPIPE, current, 0);
 501                         if (!ret)
 502                                 ret = -EPIPE;
 503                         break;
 504                 }
 505
 506                 head = pipe->head;
 507                 if (!pipe_full(head, pipe->tail, pipe->max_usage)) {
 508                         unsigned int mask = pipe->ring_size - 1;
 509                         struct pipe_buffer *buf = &pipe->bufs[head & mask];
 510                         struct page *page = pipe->tmp_page;
 511                         int copied;
 512
 513                         if (!page) {
 514                                 page = alloc_page(GFP_HIGHUSER | __GFP_ACCOUNT);
 515                                 if (unlikely(!page)) {
 516                                         ret = ret ? : -ENOMEM;
 517                                         break;
 518                                 }
 519                                 pipe->tmp_page = page;
 520                         }
 521
 522                         /* Allocate a slot in the ring in advance and attach an
 523                          * empty buffer.  If we fault or otherwise fail to use
 524                          * it, either the reader will consume it or it'll still
 525                          * be there for the next write.
 526                          */
 527                         spin_lock_irq(&pipe->rd_wait.lock);
 528
 529                         head = pipe->head;
 530                         if (pipe_full(head, pipe->tail, pipe->max_usage)) {
 531                                 spin_unlock_irq(&pipe->rd_wait.lock);
 532                                 continue;
 533                         }
 534
 535                         pipe->head = head + 1;
 536                         spin_unlock_irq(&pipe->rd_wait.lock);
 537
 538                         /* Insert it into the buffer array */
 539                         buf = &pipe->bufs[head & mask];
 540                         buf->page = page;
 541                         buf->ops = &anon_pipe_buf_ops;
 542                         buf->offset = 0;
 543                         buf->len = 0;
 544                         buf->flags = 0;
 545                         if (is_packetized(filp)) {
 546                                 buf->ops = &packet_pipe_buf_ops;
 547                                 buf->flags = PIPE_BUF_FLAG_PACKET;
 548                         }
 549                         pipe->tmp_page = NULL;
 550
 551                         copied = copy_page_from_iter(page, 0, PAGE_SIZE, from);
 552                         if (unlikely(copied < PAGE_SIZE && iov_iter_count(from))) {
 553                                 if (!ret)
 554                                         ret = -EFAULT;
 555                                 break;
 556                         }
 557                         ret += copied;
 558                         buf->offset = 0;
 559                         buf->len = copied;
 560
 561                         if (!iov_iter_count(from))
 562                                 break;
 563                 }
 564
 565                 if (!pipe_full(head, pipe->tail, pipe->max_usage))
 566                         continue;
 567
 568                 /* Wait for buffer space to become available. */
 569                 if (filp->f_flags & O_NONBLOCK) {
 570                         if (!ret)
 571                                 ret = -EAGAIN;
 572                         break;
 573                 }
 574                 if (signal_pending(current)) {
 575                         if (!ret)
 576                                 ret = -ERESTARTSYS;
 577                         break;
 578                 }
 579
 580                 /*
 581                  * We're going to release the pipe lock and wait for more
 582                  * space. We wake up any readers if necessary, and then
 583                  * after waiting we need to re-check whether the pipe
 584                  * become empty while we dropped the lock.
 585                  */
 586                 __pipe_unlock(pipe);
 587                 if (was_empty) {
 588                         wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
 589                         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 590                 }
 591                 wait_event_interruptible_exclusive(pipe->wr_wait, pipe_writable(pipe));
 592                 __pipe_lock(pipe);
 593                 was_empty = pipe_empty(pipe->head, pipe->tail);
 594                 wake_next_writer = true;
 595         }
 596 out:
 597         if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
 598                 wake_next_writer = false;
 599         __pipe_unlock(pipe);
 600
 601         /*
 602          * If we do do a wakeup event, we do a 'sync' wakeup, because we
 603          * want the reader to start processing things asap, rather than
 604          * leave the data pending.
 605          *
 606          * This is particularly important for small writes, because of
 607          * how (for example) the GNU make jobserver uses small writes to
 608          * wake up pending jobs
 609          */
 610         if (was_empty) {
 611                 wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
 612                 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 613         }
 614         if (wake_next_writer)
 615                 wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);
 616         if (ret > 0 && sb_start_write_trylock(file_inode(filp)->i_sb)) {
 617                 int err = file_update_time(filp);
 618                 if (err)
 619                         ret = err;
 620                 sb_end_write(file_inode(filp)->i_sb);
 621         }
 622         return ret;
 623 }
 624
 625 static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 626 {
 627         struct pipe_inode_info *pipe = filp->private_data;
 628         int count, head, tail, mask;
 629
 630         switch (cmd) {
 631                 case FIONREAD:
 632                         __pipe_lock(pipe);
 633                         count = 0;
 634                         head = pipe->head;
 635                         tail = pipe->tail;
 636                         mask = pipe->ring_size - 1;
 637
 638                         while (tail != head) {
 639                                 count += pipe->bufs[tail & mask].len;
 640                                 tail++;
 641                         }
 642                         __pipe_unlock(pipe);
 643
 644                         return put_user(count, (int __user *)arg);
 645                 default:
 646                         return -ENOIOCTLCMD;
 647         }
 648 }
 649
 650 /* No kernel lock held - fine */
 651 static __poll_t
 652 pipe_poll(struct file *filp, poll_table *wait)
 653 {
 654         __poll_t mask;
 655         struct pipe_inode_info *pipe = filp->private_data;
 656         unsigned int head, tail;
 657
 658         /*
 659          * Reading pipe state only -- no need for acquiring the semaphore.
 660          *
 661          * But because this is racy, the code has to add the
 662          * entry to the poll table _first_ ..
 663          */
 664         if (filp->f_mode & FMODE_READ)
 665                 poll_wait(filp, &pipe->rd_wait, wait);
 666         if (filp->f_mode & FMODE_WRITE)
 667                 poll_wait(filp, &pipe->wr_wait, wait);
 668
 669         /*
 670          * .. and only then can you do the racy tests. That way,
 671          * if something changes and you got it wrong, the poll
 672          * table entry will wake you up and fix it.
 673          */
 674         head = READ_ONCE(pipe->head);
 675         tail = READ_ONCE(pipe->tail);
 676
 677         mask = 0;
 678         if (filp->f_mode & FMODE_READ) {
 679                 if (!pipe_empty(head, tail))
 680                         mask |= EPOLLIN | EPOLLRDNORM;
 681                 if (!pipe->writers && filp->f_version != pipe->w_counter)
 682                         mask |= EPOLLHUP;
 683         }
 684
 685         if (filp->f_mode & FMODE_WRITE) {
 686                 if (!pipe_full(head, tail, pipe->max_usage))
 687                         mask |= EPOLLOUT | EPOLLWRNORM;
 688                 /*
 689                  * Most Unices do not set EPOLLERR for FIFOs but on Linux they
 690                  * behave exactly like pipes for poll().
 691                  */
 692                 if (!pipe->readers)
 693                         mask |= EPOLLERR;
 694         }
 695
 696         return mask;
 697 }
 698
 699 static void put_pipe_info(struct inode *inode, struct pipe_inode_info *pipe)
 700 {
 701         int kill = 0;
 702
 703         spin_lock(&inode->i_lock);
 704         if (!--pipe->files) {
 705                 inode->i_pipe = NULL;
 706                 kill = 1;
 707         }
 708         spin_unlock(&inode->i_lock);
 709
 710         if (kill)
 711                 free_pipe_info(pipe);
 712 }
 713
 714 static int
 715 pipe_release(struct inode *inode, struct file *file)
 716 {
 717         struct pipe_inode_info *pipe = file->private_data;
 718
 719         __pipe_lock(pipe);
 720         if (file->f_mode & FMODE_READ)
 721                 pipe->readers--;
 722         if (file->f_mode & FMODE_WRITE)
 723                 pipe->writers--;
 724
 725         /* Was that the last reader or writer, but not the other side? */
 726         if (!pipe->readers != !pipe->writers) {
 727                 wake_up_interruptible_all(&pipe->rd_wait);
 728                 wake_up_interruptible_all(&pipe->wr_wait);
 729                 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 730                 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
 731         }
 732         __pipe_unlock(pipe);
 733
 734         put_pipe_info(inode, pipe);
 735         return 0;
 736 }
 737
 738 static int
 739 pipe_fasync(int fd, struct file *filp, int on)
 740 {
 741         struct pipe_inode_info *pipe = filp->private_data;
 742         int retval = 0;
 743
 744         __pipe_lock(pipe);
 745         if (filp->f_mode & FMODE_READ)
 746                 retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);
 747         if ((filp->f_mode & FMODE_WRITE) && retval >= 0) {
 748                 retval = fasync_helper(fd, filp, on, &pipe->fasync_writers);
 749                 if (retval < 0 && (filp->f_mode & FMODE_READ))
 750                         /* this can happen only if on == T */
 751                         fasync_helper(-1, filp, 0, &pipe->fasync_readers);
 752         }
 753         __pipe_unlock(pipe);
 754         return retval;
 755 }
 756
 757 static unsigned long account_pipe_buffers(struct user_struct *user,
 758                                  unsigned long old, unsigned long new)
 759 {
 760         return atomic_long_add_return(new - old, &user->pipe_bufs);
 761 }
 762
 763 static bool too_many_pipe_buffers_soft(unsigned long user_bufs)
 764 {
 765         unsigned long soft_limit = READ_ONCE(pipe_user_pages_soft);
 766
 767         return soft_limit && user_bufs > soft_limit;
 768 }
 769
 770 static bool too_many_pipe_buffers_hard(unsigned long user_bufs)
 771 {
 772         unsigned long hard_limit = READ_ONCE(pipe_user_pages_hard);
 773
 774         return hard_limit && user_bufs > hard_limit;
 775 }
 776
 777 static bool is_unprivileged_user(void)
 778 {
 779         return !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN);
 780 }
 781
 782 struct pipe_inode_info *alloc_pipe_info(void)
 783 {
 784         struct pipe_inode_info *pipe;
 785         unsigned long pipe_bufs = PIPE_DEF_BUFFERS;
 786         struct user_struct *user = get_current_user();
 787         unsigned long user_bufs;
 788         unsigned int max_size = READ_ONCE(pipe_max_size);
 789
 790         pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL_ACCOUNT);
 791         if (pipe == NULL)
 792                 goto out_free_uid;
 793
 794         if (pipe_bufs * PAGE_SIZE > max_size && !capable(CAP_SYS_RESOURCE))
 795                 pipe_bufs = max_size >> PAGE_SHIFT;
 796
 797         user_bufs = account_pipe_buffers(user, 0, pipe_bufs);
 798
 799         if (too_many_pipe_buffers_soft(user_bufs) && is_unprivileged_user()) {
 800                 user_bufs = account_pipe_buffers(user, pipe_bufs, 1);
 801                 pipe_bufs = 1;
 802         }
 803
 804         if (too_many_pipe_buffers_hard(user_bufs) && is_unprivileged_user())
 805                 goto out_revert_acct;
 806
 807         pipe->bufs = kcalloc(pipe_bufs, sizeof(struct pipe_buffer),
 808                              GFP_KERNEL_ACCOUNT);
 809
 810         if (pipe->bufs) {
 811                 init_waitqueue_head(&pipe->rd_wait);
 812                 init_waitqueue_head(&pipe->wr_wait);
 813                 pipe->r_counter = pipe->w_counter = 1;
 814                 pipe->max_usage = pipe_bufs;
 815                 pipe->ring_size = pipe_bufs;
 816                 pipe->user = user;
 817                 mutex_init(&pipe->mutex);
 818                 return pipe;
 819         }
 820
 821 out_revert_acct:
 822         (void) account_pipe_buffers(user, pipe_bufs, 0);
 823         kfree(pipe);
 824 out_free_uid:
 825         free_uid(user);
 826         return NULL;
 827 }
 828
 829 void free_pipe_info(struct pipe_inode_info *pipe)
 830 {
 831         int i;
 832
 833         (void) account_pipe_buffers(pipe->user, pipe->ring_size, 0);
 834         free_uid(pipe->user);
 835         for (i = 0; i < pipe->ring_size; i++) {
 836                 struct pipe_buffer *buf = pipe->bufs + i;
 837                 if (buf->ops)
 838                         pipe_buf_release(pipe, buf);
 839         }
 840         if (pipe->tmp_page)
 841                 __free_page(pipe->tmp_page);
 842         kfree(pipe->bufs);
 843         kfree(pipe);
 844 }
 845
 846 static struct vfsmount *pipe_mnt __read_mostly;
 847
 848 /*
 849  * pipefs_dname() is called from d_path().
 850  */
 851 static char *pipefs_dname(struct dentry *dentry, char *buffer, int buflen)
 852 {
 853         return dynamic_dname(dentry, buffer, buflen, "pipe:[%lu]",
 854                                 d_inode(dentry)->i_ino);
 855 }
 856
 857 static const struct dentry_operations pipefs_dentry_operations = {
 858         .d_dname        = pipefs_dname,
 859 };
 860
 861 static struct inode * get_pipe_inode(void)
 862 {
 863         struct inode *inode = new_inode_pseudo(pipe_mnt->mnt_sb);
 864         struct pipe_inode_info *pipe;
 865
 866         if (!inode)
 867                 goto fail_inode;
 868
 869         inode->i_ino = get_next_ino();
 870
 871         pipe = alloc_pipe_info();
 872         if (!pipe)
 873                 goto fail_iput;
 874
 875         inode->i_pipe = pipe;
 876         pipe->files = 2;
 877         pipe->readers = pipe->writers = 1;
 878         inode->i_fop = &pipefifo_fops;
 879
 880         /*
 881          * Mark the inode dirty from the very beginning,
 882          * that way it will never be moved to the dirty
 883          * list because "mark_inode_dirty()" will think
 884          * that it already _is_ on the dirty list.
 885          */
 886         inode->i_state = I_DIRTY;
 887         inode->i_mode = S_IFIFO | S_IRUSR | S_IWUSR;
 888         inode->i_uid = current_fsuid();
 889         inode->i_gid = current_fsgid();
 890         inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
 891
 892         return inode;
 893
 894 fail_iput:
 895         iput(inode);
 896
 897 fail_inode:
 898         return NULL;
 899 }
 900
 901 int create_pipe_files(struct file **res, int flags)
 902 {
 903         struct inode *inode = get_pipe_inode();
 904         struct file *f;
 905
 906         if (!inode)
 907                 return -ENFILE;
 908
 909         f = alloc_file_pseudo(inode, pipe_mnt, "",
 910                                 O_WRONLY | (flags & (O_NONBLOCK | O_DIRECT)),
 911                                 &pipefifo_fops);
 912         if (IS_ERR(f)) {
 913                 free_pipe_info(inode->i_pipe);
 914                 iput(inode);
 915                 return PTR_ERR(f);
 916         }
 917
 918         f->private_data = inode->i_pipe;
 919
 920         res[0] = alloc_file_clone(f, O_RDONLY | (flags & O_NONBLOCK),
 921                                   &pipefifo_fops);
 922         if (IS_ERR(res[0])) {
 923                 put_pipe_info(inode, inode->i_pipe);
 924                 fput(f);
 925                 return PTR_ERR(res[0]);
 926         }
 927         res[0]->private_data = inode->i_pipe;
 928         res[1] = f;
 929         stream_open(inode, res[0]);
 930         stream_open(inode, res[1]);
 931         return 0;
 932 }
 933
 934 static int __do_pipe_flags(int *fd, struct file **files, int flags)
 935 {
 936         int error;
 937         int fdw, fdr;
 938
 939         if (flags & ~(O_CLOEXEC | O_NONBLOCK | O_DIRECT))
 940                 return -EINVAL;
 941
 942         error = create_pipe_files(files, flags);
 943         if (error)
 944                 return error;
 945
 946         error = get_unused_fd_flags(flags);
 947         if (error < 0)
 948                 goto err_read_pipe;
 949         fdr = error;
 950
 951         error = get_unused_fd_flags(flags);
 952         if (error < 0)
 953                 goto err_fdr;
 954         fdw = error;
 955
 956         audit_fd_pair(fdr, fdw);
 957         fd[0] = fdr;
 958         fd[1] = fdw;
 959         return 0;
 960
 961  err_fdr:
 962         put_unused_fd(fdr);
 963  err_read_pipe:
 964         fput(files[0]);
 965         fput(files[1]);
 966         return error;
 967 }
 968
 969 int do_pipe_flags(int *fd, int flags)
 970 {
 971         struct file *files[2];
 972         int error = __do_pipe_flags(fd, files, flags);
 973         if (!error) {
 974                 fd_install(fd[0], files[0]);
 975                 fd_install(fd[1], files[1]);
 976         }
 977         return error;
 978 }
 979
 980 /*
 981  * sys_pipe() is the normal C calling standard for creating
 982  * a pipe. It's not the way Unix traditionally does this, though.
 983  */
 984 static int do_pipe2(int __user *fildes, int flags)
 985 {
 986         struct file *files[2];
 987         int fd[2];
 988         int error;
 989
 990         error = __do_pipe_flags(fd, files, flags);
 991         if (!error) {
 992                 if (unlikely(copy_to_user(fildes, fd, sizeof(fd)))) {
 993                         fput(files[0]);
 994                         fput(files[1]);
 995                         put_unused_fd(fd[0]);
 996                         put_unused_fd(fd[1]);
 997                         error = -EFAULT;
 998                 } else {
 999                         fd_install(fd[0], files[0]);
1000                         fd_install(fd[1], files[1]);
1001                 }
1002         }
1003         return error;
1004 }
1005
1006 SYSCALL_DEFINE2(pipe2, int __user *, fildes, int, flags)
1007 {
1008         return do_pipe2(fildes, flags);
1009 }
1010
1011 SYSCALL_DEFINE1(pipe, int __user *, fildes)
1012 {
1013         return do_pipe2(fildes, 0);
1014 }
1015
1016 static int wait_for_partner(struct pipe_inode_info *pipe, unsigned int *cnt)
1017 {
1018         int cur = *cnt;
1019
1020         while (cur == *cnt) {
1021                 pipe_wait(pipe);
1022                 if (signal_pending(current))
1023                         break;
1024         }
1025         return cur == *cnt ? -ERESTARTSYS : 0;
1026 }
1027
1028 static void wake_up_partner(struct pipe_inode_info *pipe)
1029 {
1030         wake_up_interruptible_all(&pipe->rd_wait);
1031         wake_up_interruptible_all(&pipe->wr_wait);
1032 }
1033
1034 static int fifo_open(struct inode *inode, struct file *filp)
1035 {
1036         struct pipe_inode_info *pipe;
1037         bool is_pipe = inode->i_sb->s_magic == PIPEFS_MAGIC;
1038         int ret;
1039
1040         filp->f_version = 0;
1041
1042         spin_lock(&inode->i_lock);
1043         if (inode->i_pipe) {
1044                 pipe = inode->i_pipe;
1045                 pipe->files++;
1046                 spin_unlock(&inode->i_lock);
1047         } else {
1048                 spin_unlock(&inode->i_lock);
1049                 pipe = alloc_pipe_info();
1050                 if (!pipe)
1051                         return -ENOMEM;
1052                 pipe->files = 1;
1053                 spin_lock(&inode->i_lock);
1054                 if (unlikely(inode->i_pipe)) {
1055                         inode->i_pipe->files++;
1056                         spin_unlock(&inode->i_lock);
1057                         free_pipe_info(pipe);
1058                         pipe = inode->i_pipe;
1059                 } else {
1060                         inode->i_pipe = pipe;
1061                         spin_unlock(&inode->i_lock);
1062                 }
1063         }
1064         filp->private_data = pipe;
1065         /* OK, we have a pipe and it's pinned down */
1066
1067         __pipe_lock(pipe);
1068
1069         /* We can only do regular read/write on fifos */
1070         stream_open(inode, filp);
1071
1072         switch (filp->f_mode & (FMODE_READ | FMODE_WRITE)) {
1073         case FMODE_READ:
1074         /*
1075          *  O_RDONLY
1076          *  POSIX.1 says that O_NONBLOCK means return with the FIFO
1077          *  opened, even when there is no process writing the FIFO.
1078          */
1079                 pipe->r_counter++;
1080                 if (pipe->readers++ == 0)
1081                         wake_up_partner(pipe);
1082
1083                 if (!is_pipe && !pipe->writers) {
1084                         if ((filp->f_flags & O_NONBLOCK)) {
1085                                 /* suppress EPOLLHUP until we have
1086                                  * seen a writer */
1087                                 filp->f_version = pipe->w_counter;
1088                         } else {
1089                                 if (wait_for_partner(pipe, &pipe->w_counter))
1090                                         goto err_rd;
1091                         }
1092                 }
1093                 break;
1094
1095         case FMODE_WRITE:
1096         /*
1097          *  O_WRONLY
1098          *  POSIX.1 says that O_NONBLOCK means return -1 with
1099          *  errno=ENXIO when there is no process reading the FIFO.
1100          */
1101                 ret = -ENXIO;
1102                 if (!is_pipe && (filp->f_flags & O_NONBLOCK) && !pipe->readers)
1103                         goto err;
1104
1105                 pipe->w_counter++;
1106                 if (!pipe->writers++)
1107                         wake_up_partner(pipe);
1108
1109                 if (!is_pipe && !pipe->readers) {
1110                         if (wait_for_partner(pipe, &pipe->r_counter))
1111                                 goto err_wr;
1112                 }
1113                 break;
1114
1115         case FMODE_READ | FMODE_WRITE:
1116         /*
1117          *  O_RDWR
1118          *  POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
1119          *  This implementation will NEVER block on a O_RDWR open, since
1120          *  the process can at least talk to itself.
1121          */
1122
1123                 pipe->readers++;
1124                 pipe->writers++;
1125                 pipe->r_counter++;
1126                 pipe->w_counter++;
1127                 if (pipe->readers == 1 || pipe->writers == 1)
1128                         wake_up_partner(pipe);
1129                 break;
1130
1131         default:
1132                 ret = -EINVAL;
1133                 goto err;
1134         }
1135
1136         /* Ok! */
1137         __pipe_unlock(pipe);
1138         return 0;
1139
1140 err_rd:
1141         if (!--pipe->readers)
1142                 wake_up_interruptible(&pipe->wr_wait);
1143         ret = -ERESTARTSYS;
1144         goto err;
1145
1146 err_wr:
1147         if (!--pipe->writers)
1148                 wake_up_interruptible_all(&pipe->rd_wait);
1149         ret = -ERESTARTSYS;
1150         goto err;
1151
1152 err:
1153         __pipe_unlock(pipe);
1154
1155         put_pipe_info(inode, pipe);
1156         return ret;
1157 }
1158
1159 const struct file_operations pipefifo_fops = {
1160         .open           = fifo_open,
1161         .llseek         = no_llseek,
1162         .read_iter      = pipe_read,
1163         .write_iter     = pipe_write,
1164         .poll           = pipe_poll,
1165         .unlocked_ioctl = pipe_ioctl,
1166         .release        = pipe_release,
1167         .fasync         = pipe_fasync,
1168 };
1169
1170 /*
1171  * Currently we rely on the pipe array holding a power-of-2 number
1172  * of pages. Returns 0 on error.
1173  */
1174 unsigned int round_pipe_size(unsigned long size)
1175 {
1176         if (size > (1U << 31))
1177                 return 0;
1178
1179         /* Minimum pipe size, as required by POSIX */
1180         if (size < PAGE_SIZE)
1181                 return PAGE_SIZE;
1182
1183         return roundup_pow_of_two(size);
1184 }
1185
1186 /*
1187  * Allocate a new array of pipe buffers and copy the info over. Returns the
1188  * pipe size if successful, or return -ERROR on error.
1189  */
1190 static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
1191 {
1192         struct pipe_buffer *bufs;
1193         unsigned int size, nr_slots, head, tail, mask, n;
1194         unsigned long user_bufs;
1195         long ret = 0;
1196
1197         size = round_pipe_size(arg);
1198         nr_slots = size >> PAGE_SHIFT;
1199
1200         if (!nr_slots)
1201                 return -EINVAL;
1202
1203         /*
1204          * If trying to increase the pipe capacity, check that an
1205          * unprivileged user is not trying to exceed various limits
1206          * (soft limit check here, hard limit check just below).
1207          * Decreasing the pipe capacity is always permitted, even
1208          * if the user is currently over a limit.
1209          */
1210         if (nr_slots > pipe->ring_size &&
1211                         size > pipe_max_size && !capable(CAP_SYS_RESOURCE))
1212                 return -EPERM;
1213
1214         user_bufs = account_pipe_buffers(pipe->user, pipe->ring_size, nr_slots);
1215
1216         if (nr_slots > pipe->ring_size &&
1217                         (too_many_pipe_buffers_hard(user_bufs) ||
1218                          too_many_pipe_buffers_soft(user_bufs)) &&
1219                         is_unprivileged_user()) {
1220                 ret = -EPERM;
1221                 goto out_revert_acct;
1222         }
1223
1224         /*
1225          * We can shrink the pipe, if arg is greater than the ring occupancy.
1226          * Since we don't expect a lot of shrink+grow operations, just free and
1227          * allocate again like we would do for growing.  If the pipe currently
1228          * contains more buffers than arg, then return busy.
1229          */
1230         mask = pipe->ring_size - 1;
1231         head = pipe->head;
1232         tail = pipe->tail;
1233         n = pipe_occupancy(pipe->head, pipe->tail);
1234         if (nr_slots < n) {
1235                 ret = -EBUSY;
1236                 goto out_revert_acct;
1237         }
1238
1239         bufs = kcalloc(nr_slots, sizeof(*bufs),
1240                        GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
1241         if (unlikely(!bufs)) {
1242                 ret = -ENOMEM;
1243                 goto out_revert_acct;
1244         }
1245
1246         /*
1247          * The pipe array wraps around, so just start the new one at zero
1248          * and adjust the indices.
1249          */
1250         if (n > 0) {
1251                 unsigned int h = head & mask;
1252                 unsigned int t = tail & mask;
1253                 if (h > t) {
1254                         memcpy(bufs, pipe->bufs + t,
1255                                n * sizeof(struct pipe_buffer));
1256                 } else {
1257                         unsigned int tsize = pipe->ring_size - t;
1258                         if (h > 0)
1259                                 memcpy(bufs + tsize, pipe->bufs,
1260                                        h * sizeof(struct pipe_buffer));
1261                         memcpy(bufs, pipe->bufs + t,
1262                                tsize * sizeof(struct pipe_buffer));
1263                 }
1264         }
1265
1266         head = n;
1267         tail = 0;
1268
1269         kfree(pipe->bufs);
1270         pipe->bufs = bufs;
1271         pipe->ring_size = nr_slots;
1272         pipe->max_usage = nr_slots;
1273         pipe->tail = tail;
1274         pipe->head = head;
1275
1276         /* This might have made more room for writers */
1277         wake_up_interruptible(&pipe->wr_wait);
1278         return pipe->max_usage * PAGE_SIZE;
1279
1280 out_revert_acct:
1281         (void) account_pipe_buffers(pipe->user, nr_slots, pipe->ring_size);
1282         return ret;
1283 }
1284
1285 /*
1286  * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same
1287  * location, so checking ->i_pipe is not enough to verify that this is a
1288  * pipe.
1289  */
1290 struct pipe_inode_info *get_pipe_info(struct file *file)
1291 {
1292         return file->f_op == &pipefifo_fops ? file->private_data : NULL;
1293 }
1294
1295 long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
1296 {
1297         struct pipe_inode_info *pipe;
1298         long ret;
1299
1300         pipe = get_pipe_info(file);
1301         if (!pipe)
1302                 return -EBADF;
1303
1304         __pipe_lock(pipe);
1305
1306         switch (cmd) {
1307         case F_SETPIPE_SZ:
1308                 ret = pipe_set_size(pipe, arg);
1309                 break;
1310         case F_GETPIPE_SZ:
1311                 ret = pipe->max_usage * PAGE_SIZE;
1312                 break;
1313         default:
1314                 ret = -EINVAL;
1315                 break;
1316         }
1317
1318         __pipe_unlock(pipe);
1319         return ret;
1320 }
1321
1322 static const struct super_operations pipefs_ops = {
1323         .destroy_inode = free_inode_nonrcu,
1324         .statfs = simple_statfs,
1325 };
1326
1327 /*
1328  * pipefs should _never_ be mounted by userland - too much of security hassle,
1329  * no real gain from having the whole whorehouse mounted. So we don't need
1330  * any operations on the root directory. However, we need a non-trivial
1331  * d_name - pipe: will go nicely and kill the special-casing in procfs.
1332  */
1333
1334 static int pipefs_init_fs_context(struct fs_context *fc)
1335 {
1336         struct pseudo_fs_context *ctx = init_pseudo(fc, PIPEFS_MAGIC);
1337         if (!ctx)
1338                 return -ENOMEM;
1339         ctx->ops = &pipefs_ops;
1340         ctx->dops = &pipefs_dentry_operations;
1341         return 0;
1342 }
1343
1344 static struct file_system_type pipe_fs_type = {
1345         .name           = "pipefs",
1346         .init_fs_context = pipefs_init_fs_context,
1347         .kill_sb        = kill_anon_super,
1348 };
1349
1350 static int __init init_pipe_fs(void)
1351 {
1352         int err = register_filesystem(&pipe_fs_type);
1353
1354         if (!err) {
1355                 pipe_mnt = kern_mount(&pipe_fs_type);
1356                 if (IS_ERR(pipe_mnt)) {
1357                         err = PTR_ERR(pipe_mnt);
1358                         unregister_filesystem(&pipe_fs_type);
1359                 }
1360         }
1361         return err;
1362 }
1363
1364 fs_initcall(init_pipe_fs);