fs/iomap/direct-io.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2010 Red Hat, Inc.
   4  * Copyright (c) 2016-2021 Christoph Hellwig.
   5  */
   6 #include <linux/module.h>
   7 #include <linux/compiler.h>
   8 #include <linux/fs.h>
   9 #include <linux/fscrypt.h>
  10 #include <linux/pagemap.h>
  11 #include <linux/iomap.h>
  12 #include <linux/backing-dev.h>
  13 #include <linux/uio.h>
  14 #include <linux/task_io_accounting_ops.h>
  15 #include "trace.h"
  16
  17 #include "../internal.h"
  18
  19 /*
  20  * Private flags for iomap_dio, must not overlap with the public ones in
  21  * iomap.h:
  22  */
  23 #define IOMAP_DIO_WRITE_FUA     (1 << 28)
  24 #define IOMAP_DIO_NEED_SYNC     (1 << 29)
  25 #define IOMAP_DIO_WRITE         (1 << 30)
  26 #define IOMAP_DIO_DIRTY         (1 << 31)
  27
  28 struct iomap_dio {
  29         struct kiocb            *iocb;
  30         const struct iomap_dio_ops *dops;
  31         loff_t                  i_size;
  32         loff_t                  size;
  33         atomic_t                ref;
  34         unsigned                flags;
  35         int                     error;
  36         size_t                  done_before;
  37         bool                    wait_for_completion;
  38
  39         union {
  40                 /* used during submission and for synchronous completion: */
  41                 struct {
  42                         struct iov_iter         *iter;
  43                         struct task_struct      *waiter;
  44                         struct bio              *poll_bio;
  45                 } submit;
  46
  47                 /* used for aio completion: */
  48                 struct {
  49                         struct work_struct      work;
  50                 } aio;
  51         };
  52 };
  53
  54 static struct bio *iomap_dio_alloc_bio(const struct iomap_iter *iter,
  55                 struct iomap_dio *dio, unsigned short nr_vecs, blk_opf_t opf)
  56 {
  57         if (dio->dops && dio->dops->bio_set)
  58                 return bio_alloc_bioset(iter->iomap.bdev, nr_vecs, opf,
  59                                         GFP_KERNEL, dio->dops->bio_set);
  60         return bio_alloc(iter->iomap.bdev, nr_vecs, opf, GFP_KERNEL);
  61 }
  62
  63 static void iomap_dio_submit_bio(const struct iomap_iter *iter,
  64                 struct iomap_dio *dio, struct bio *bio, loff_t pos)
  65 {
  66         atomic_inc(&dio->ref);
  67
  68         /* Sync dio can't be polled reliably */
  69         if ((dio->iocb->ki_flags & IOCB_HIPRI) && !is_sync_kiocb(dio->iocb)) {
  70                 bio_set_polled(bio, dio->iocb);
  71                 dio->submit.poll_bio = bio;
  72         }
  73
  74         if (dio->dops && dio->dops->submit_io)
  75                 dio->dops->submit_io(iter, bio, pos);
  76         else
  77                 submit_bio(bio);
  78 }
  79
  80 ssize_t iomap_dio_complete(struct iomap_dio *dio)
  81 {
  82         const struct iomap_dio_ops *dops = dio->dops;
  83         struct kiocb *iocb = dio->iocb;
  84         loff_t offset = iocb->ki_pos;
  85         ssize_t ret = dio->error;
  86
  87         if (dops && dops->end_io)
  88                 ret = dops->end_io(iocb, dio->size, ret, dio->flags);
  89
  90         if (likely(!ret)) {
  91                 ret = dio->size;
  92                 /* check for short read */
  93                 if (offset + ret > dio->i_size &&
  94                     !(dio->flags & IOMAP_DIO_WRITE))
  95                         ret = dio->i_size - offset;
  96         }
  97
  98         /*
  99          * Try again to invalidate clean pages which might have been cached by
 100          * non-direct readahead, or faulted in by get_user_pages() if the source
 101          * of the write was an mmap'ed region of the file we're writing.  Either
 102          * one is a pretty crazy thing to do, so we don't support it 100%.  If
 103          * this invalidation fails, tough, the write still worked...
 104          *
 105          * And this page cache invalidation has to be after ->end_io(), as some
 106          * filesystems convert unwritten extents to real allocations in
 107          * ->end_io() when necessary, otherwise a racing buffer read would cache
 108          * zeros from unwritten extents.
 109          */
 110         if (!dio->error && dio->size && (dio->flags & IOMAP_DIO_WRITE))
 111                 kiocb_invalidate_post_direct_write(iocb, dio->size);
 112
 113         inode_dio_end(file_inode(iocb->ki_filp));
 114
 115         if (ret > 0) {
 116                 iocb->ki_pos += ret;
 117
 118                 /*
 119                  * If this is a DSYNC write, make sure we push it to stable
 120                  * storage now that we've written data.
 121                  */
 122                 if (dio->flags & IOMAP_DIO_NEED_SYNC)
 123                         ret = generic_write_sync(iocb, ret);
 124                 if (ret > 0)
 125                         ret += dio->done_before;
 126         }
 127         trace_iomap_dio_complete(iocb, dio->error, ret);
 128         kfree(dio);
 129         return ret;
 130 }
 131 EXPORT_SYMBOL_GPL(iomap_dio_complete);
 132
 133 static void iomap_dio_complete_work(struct work_struct *work)
 134 {
 135         struct iomap_dio *dio = container_of(work, struct iomap_dio, aio.work);
 136         struct kiocb *iocb = dio->iocb;
 137
 138         iocb->ki_complete(iocb, iomap_dio_complete(dio));
 139 }
 140
 141 /*
 142  * Set an error in the dio if none is set yet.  We have to use cmpxchg
 143  * as the submission context and the completion context(s) can race to
 144  * update the error.
 145  */
 146 static inline void iomap_dio_set_error(struct iomap_dio *dio, int ret)
 147 {
 148         cmpxchg(&dio->error, 0, ret);
 149 }
 150
 151 void iomap_dio_bio_end_io(struct bio *bio)
 152 {
 153         struct iomap_dio *dio = bio->bi_private;
 154         bool should_dirty = (dio->flags & IOMAP_DIO_DIRTY);
 155
 156         if (bio->bi_status)
 157                 iomap_dio_set_error(dio, blk_status_to_errno(bio->bi_status));
 158
 159         if (atomic_dec_and_test(&dio->ref)) {
 160                 if (dio->wait_for_completion) {
 161                         struct task_struct *waiter = dio->submit.waiter;
 162                         WRITE_ONCE(dio->submit.waiter, NULL);
 163                         blk_wake_io_task(waiter);
 164                 } else if (dio->flags & IOMAP_DIO_WRITE) {
 165                         struct inode *inode = file_inode(dio->iocb->ki_filp);
 166
 167                         WRITE_ONCE(dio->iocb->private, NULL);
 168                         INIT_WORK(&dio->aio.work, iomap_dio_complete_work);
 169                         queue_work(inode->i_sb->s_dio_done_wq, &dio->aio.work);
 170                 } else {
 171                         WRITE_ONCE(dio->iocb->private, NULL);
 172                         iomap_dio_complete_work(&dio->aio.work);
 173                 }
 174         }
 175
 176         if (should_dirty) {
 177                 bio_check_pages_dirty(bio);
 178         } else {
 179                 bio_release_pages(bio, false);
 180                 bio_put(bio);
 181         }
 182 }
 183 EXPORT_SYMBOL_GPL(iomap_dio_bio_end_io);
 184
 185 static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
 186                 loff_t pos, unsigned len)
 187 {
 188         struct inode *inode = file_inode(dio->iocb->ki_filp);
 189         struct page *page = ZERO_PAGE(0);
 190         struct bio *bio;
 191
 192         bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
 193         fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
 194                                   GFP_KERNEL);
 195         bio->bi_iter.bi_sector = iomap_sector(&iter->iomap, pos);
 196         bio->bi_private = dio;
 197         bio->bi_end_io = iomap_dio_bio_end_io;
 198
 199         __bio_add_page(bio, page, len, 0);
 200         iomap_dio_submit_bio(iter, dio, bio, pos);
 201 }
 202
 203 /*
 204  * Figure out the bio's operation flags from the dio request, the
 205  * mapping, and whether or not we want FUA.  Note that we can end up
 206  * clearing the WRITE_FUA flag in the dio request.
 207  */
 208 static inline blk_opf_t iomap_dio_bio_opflags(struct iomap_dio *dio,
 209                 const struct iomap *iomap, bool use_fua)
 210 {
 211         blk_opf_t opflags = REQ_SYNC | REQ_IDLE;
 212
 213         if (!(dio->flags & IOMAP_DIO_WRITE))
 214                 return REQ_OP_READ;
 215
 216         opflags |= REQ_OP_WRITE;
 217         if (use_fua)
 218                 opflags |= REQ_FUA;
 219         else
 220                 dio->flags &= ~IOMAP_DIO_WRITE_FUA;
 221
 222         return opflags;
 223 }
 224
 225 static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
 226                 struct iomap_dio *dio)
 227 {
 228         const struct iomap *iomap = &iter->iomap;
 229         struct inode *inode = iter->inode;
 230         unsigned int fs_block_size = i_blocksize(inode), pad;
 231         loff_t length = iomap_length(iter);
 232         loff_t pos = iter->pos;
 233         blk_opf_t bio_opf;
 234         struct bio *bio;
 235         bool need_zeroout = false;
 236         bool use_fua = false;
 237         int nr_pages, ret = 0;
 238         size_t copied = 0;
 239         size_t orig_count;
 240
 241         if ((pos | length) & (bdev_logical_block_size(iomap->bdev) - 1) ||
 242             !bdev_iter_is_aligned(iomap->bdev, dio->submit.iter))
 243                 return -EINVAL;
 244
 245         if (iomap->type == IOMAP_UNWRITTEN) {
 246                 dio->flags |= IOMAP_DIO_UNWRITTEN;
 247                 need_zeroout = true;
 248         }
 249
 250         if (iomap->flags & IOMAP_F_SHARED)
 251                 dio->flags |= IOMAP_DIO_COW;
 252
 253         if (iomap->flags & IOMAP_F_NEW) {
 254                 need_zeroout = true;
 255         } else if (iomap->type == IOMAP_MAPPED) {
 256                 /*
 257                  * Use a FUA write if we need datasync semantics, this is a pure
 258                  * data IO that doesn't require any metadata updates (including
 259                  * after IO completion such as unwritten extent conversion) and
 260                  * the underlying device supports FUA. This allows us to avoid
 261                  * cache flushes on IO completion.
 262                  */
 263                 if (!(iomap->flags & (IOMAP_F_SHARED|IOMAP_F_DIRTY)) &&
 264                     (dio->flags & IOMAP_DIO_WRITE_FUA) && bdev_fua(iomap->bdev))
 265                         use_fua = true;
 266         }
 267
 268         /*
 269          * Save the original count and trim the iter to just the extent we
 270          * are operating on right now.  The iter will be re-expanded once
 271          * we are done.
 272          */
 273         orig_count = iov_iter_count(dio->submit.iter);
 274         iov_iter_truncate(dio->submit.iter, length);
 275
 276         if (!iov_iter_count(dio->submit.iter))
 277                 goto out;
 278
 279         /*
 280          * We can only poll for single bio I/Os.
 281          */
 282         if (need_zeroout ||
 283             ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode)))
 284                 dio->iocb->ki_flags &= ~IOCB_HIPRI;
 285
 286         if (need_zeroout) {
 287                 /* zero out from the start of the block to the write offset */
 288                 pad = pos & (fs_block_size - 1);
 289                 if (pad)
 290                         iomap_dio_zero(iter, dio, pos - pad, pad);
 291         }
 292
 293         /*
 294          * Set the operation flags early so that bio_iov_iter_get_pages
 295          * can set up the page vector appropriately for a ZONE_APPEND
 296          * operation.
 297          */
 298         bio_opf = iomap_dio_bio_opflags(dio, iomap, use_fua);
 299
 300         nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter, BIO_MAX_VECS);
 301         do {
 302                 size_t n;
 303                 if (dio->error) {
 304                         iov_iter_revert(dio->submit.iter, copied);
 305                         copied = ret = 0;
 306                         goto out;
 307                 }
 308
 309                 bio = iomap_dio_alloc_bio(iter, dio, nr_pages, bio_opf);
 310                 fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
 311                                           GFP_KERNEL);
 312                 bio->bi_iter.bi_sector = iomap_sector(iomap, pos);
 313                 bio->bi_ioprio = dio->iocb->ki_ioprio;
 314                 bio->bi_private = dio;
 315                 bio->bi_end_io = iomap_dio_bio_end_io;
 316
 317                 ret = bio_iov_iter_get_pages(bio, dio->submit.iter);
 318                 if (unlikely(ret)) {
 319                         /*
 320                          * We have to stop part way through an IO. We must fall
 321                          * through to the sub-block tail zeroing here, otherwise
 322                          * this short IO may expose stale data in the tail of
 323                          * the block we haven't written data to.
 324                          */
 325                         bio_put(bio);
 326                         goto zero_tail;
 327                 }
 328
 329                 n = bio->bi_iter.bi_size;
 330                 if (dio->flags & IOMAP_DIO_WRITE) {
 331                         task_io_account_write(n);
 332                 } else {
 333                         if (dio->flags & IOMAP_DIO_DIRTY)
 334                                 bio_set_pages_dirty(bio);
 335                 }
 336
 337                 dio->size += n;
 338                 copied += n;
 339
 340                 nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter,
 341                                                  BIO_MAX_VECS);
 342                 /*
 343                  * We can only poll for single bio I/Os.
 344                  */
 345                 if (nr_pages)
 346                         dio->iocb->ki_flags &= ~IOCB_HIPRI;
 347                 iomap_dio_submit_bio(iter, dio, bio, pos);
 348                 pos += n;
 349         } while (nr_pages);
 350
 351         /*
 352          * We need to zeroout the tail of a sub-block write if the extent type
 353          * requires zeroing or the write extends beyond EOF. If we don't zero
 354          * the block tail in the latter case, we can expose stale data via mmap
 355          * reads of the EOF block.
 356          */
 357 zero_tail:
 358         if (need_zeroout ||
 359             ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode))) {
 360                 /* zero out from the end of the write to the end of the block */
 361                 pad = pos & (fs_block_size - 1);
 362                 if (pad)
 363                         iomap_dio_zero(iter, dio, pos, fs_block_size - pad);
 364         }
 365 out:
 366         /* Undo iter limitation to current extent */
 367         iov_iter_reexpand(dio->submit.iter, orig_count - copied);
 368         if (copied)
 369                 return copied;
 370         return ret;
 371 }
 372
 373 static loff_t iomap_dio_hole_iter(const struct iomap_iter *iter,
 374                 struct iomap_dio *dio)
 375 {
 376         loff_t length = iov_iter_zero(iomap_length(iter), dio->submit.iter);
 377
 378         dio->size += length;
 379         if (!length)
 380                 return -EFAULT;
 381         return length;
 382 }
 383
 384 static loff_t iomap_dio_inline_iter(const struct iomap_iter *iomi,
 385                 struct iomap_dio *dio)
 386 {
 387         const struct iomap *iomap = &iomi->iomap;
 388         struct iov_iter *iter = dio->submit.iter;
 389         void *inline_data = iomap_inline_data(iomap, iomi->pos);
 390         loff_t length = iomap_length(iomi);
 391         loff_t pos = iomi->pos;
 392         size_t copied;
 393
 394         if (WARN_ON_ONCE(!iomap_inline_data_valid(iomap)))
 395                 return -EIO;
 396
 397         if (dio->flags & IOMAP_DIO_WRITE) {
 398                 loff_t size = iomi->inode->i_size;
 399
 400                 if (pos > size)
 401                         memset(iomap_inline_data(iomap, size), 0, pos - size);
 402                 copied = copy_from_iter(inline_data, length, iter);
 403                 if (copied) {
 404                         if (pos + copied > size)
 405                                 i_size_write(iomi->inode, pos + copied);
 406                         mark_inode_dirty(iomi->inode);
 407                 }
 408         } else {
 409                 copied = copy_to_iter(inline_data, length, iter);
 410         }
 411         dio->size += copied;
 412         if (!copied)
 413                 return -EFAULT;
 414         return copied;
 415 }
 416
 417 static loff_t iomap_dio_iter(const struct iomap_iter *iter,
 418                 struct iomap_dio *dio)
 419 {
 420         switch (iter->iomap.type) {
 421         case IOMAP_HOLE:
 422                 if (WARN_ON_ONCE(dio->flags & IOMAP_DIO_WRITE))
 423                         return -EIO;
 424                 return iomap_dio_hole_iter(iter, dio);
 425         case IOMAP_UNWRITTEN:
 426                 if (!(dio->flags & IOMAP_DIO_WRITE))
 427                         return iomap_dio_hole_iter(iter, dio);
 428                 return iomap_dio_bio_iter(iter, dio);
 429         case IOMAP_MAPPED:
 430                 return iomap_dio_bio_iter(iter, dio);
 431         case IOMAP_INLINE:
 432                 return iomap_dio_inline_iter(iter, dio);
 433         case IOMAP_DELALLOC:
 434                 /*
 435                  * DIO is not serialised against mmap() access at all, and so
 436                  * if the page_mkwrite occurs between the writeback and the
 437                  * iomap_iter() call in the DIO path, then it will see the
 438                  * DELALLOC block that the page-mkwrite allocated.
 439                  */
 440                 pr_warn_ratelimited("Direct I/O collision with buffered writes! File: %pD4 Comm: %.20s\n",
 441                                     dio->iocb->ki_filp, current->comm);
 442                 return -EIO;
 443         default:
 444                 WARN_ON_ONCE(1);
 445                 return -EIO;
 446         }
 447 }
 448
 449 /*
 450  * iomap_dio_rw() always completes O_[D]SYNC writes regardless of whether the IO
 451  * is being issued as AIO or not.  This allows us to optimise pure data writes
 452  * to use REQ_FUA rather than requiring generic_write_sync() to issue a
 453  * REQ_FLUSH post write. This is slightly tricky because a single request here
 454  * can be mapped into multiple disjoint IOs and only a subset of the IOs issued
 455  * may be pure data writes. In that case, we still need to do a full data sync
 456  * completion.
 457  *
 458  * When page faults are disabled and @dio_flags includes IOMAP_DIO_PARTIAL,
 459  * __iomap_dio_rw can return a partial result if it encounters a non-resident
 460  * page in @iter after preparing a transfer.  In that case, the non-resident
 461  * pages can be faulted in and the request resumed with @done_before set to the
 462  * number of bytes previously transferred.  The request will then complete with
 463  * the correct total number of bytes transferred; this is essential for
 464  * completing partial requests asynchronously.
 465  *
 466  * Returns -ENOTBLK In case of a page invalidation invalidation failure for
 467  * writes.  The callers needs to fall back to buffered I/O in this case.
 468  */
 469 struct iomap_dio *
 470 __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 471                 const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
 472                 unsigned int dio_flags, void *private, size_t done_before)
 473 {
 474         struct inode *inode = file_inode(iocb->ki_filp);
 475         struct iomap_iter iomi = {
 476                 .inode          = inode,
 477                 .pos            = iocb->ki_pos,
 478                 .len            = iov_iter_count(iter),
 479                 .flags          = IOMAP_DIRECT,
 480                 .private        = private,
 481         };
 482         bool wait_for_completion =
 483                 is_sync_kiocb(iocb) || (dio_flags & IOMAP_DIO_FORCE_WAIT);
 484         struct blk_plug plug;
 485         struct iomap_dio *dio;
 486         loff_t ret = 0;
 487
 488         trace_iomap_dio_rw_begin(iocb, iter, dio_flags, done_before);
 489
 490         if (!iomi.len)
 491                 return NULL;
 492
 493         dio = kmalloc(sizeof(*dio), GFP_KERNEL);
 494         if (!dio)
 495                 return ERR_PTR(-ENOMEM);
 496
 497         dio->iocb = iocb;
 498         atomic_set(&dio->ref, 1);
 499         dio->size = 0;
 500         dio->i_size = i_size_read(inode);
 501         dio->dops = dops;
 502         dio->error = 0;
 503         dio->flags = 0;
 504         dio->done_before = done_before;
 505
 506         dio->submit.iter = iter;
 507         dio->submit.waiter = current;
 508         dio->submit.poll_bio = NULL;
 509
 510         if (iocb->ki_flags & IOCB_NOWAIT)
 511                 iomi.flags |= IOMAP_NOWAIT;
 512
 513         if (iov_iter_rw(iter) == READ) {
 514                 if (iomi.pos >= dio->i_size)
 515                         goto out_free_dio;
 516
 517                 if (user_backed_iter(iter))
 518                         dio->flags |= IOMAP_DIO_DIRTY;
 519
 520                 ret = kiocb_write_and_wait(iocb, iomi.len);
 521                 if (ret)
 522                         goto out_free_dio;
 523         } else {
 524                 iomi.flags |= IOMAP_WRITE;
 525                 dio->flags |= IOMAP_DIO_WRITE;
 526
 527                 if (dio_flags & IOMAP_DIO_OVERWRITE_ONLY) {
 528                         ret = -EAGAIN;
 529                         if (iomi.pos >= dio->i_size ||
 530                             iomi.pos + iomi.len > dio->i_size)
 531                                 goto out_free_dio;
 532                         iomi.flags |= IOMAP_OVERWRITE_ONLY;
 533                 }
 534
 535                 /* for data sync or sync, we need sync completion processing */
 536                 if (iocb_is_dsync(iocb)) {
 537                         dio->flags |= IOMAP_DIO_NEED_SYNC;
 538
 539                        /*
 540                         * For datasync only writes, we optimistically try
 541                         * using FUA for this IO.  Any non-FUA write that
 542                         * occurs will clear this flag, hence we know before
 543                         * completion whether a cache flush is necessary.
 544                         */
 545                         if (!(iocb->ki_flags & IOCB_SYNC))
 546                                 dio->flags |= IOMAP_DIO_WRITE_FUA;
 547                 }
 548
 549                 /*
 550                  * Try to invalidate cache pages for the range we are writing.
 551                  * If this invalidation fails, let the caller fall back to
 552                  * buffered I/O.
 553                  */
 554                 ret = kiocb_invalidate_pages(iocb, iomi.len);
 555                 if (ret) {
 556                         if (ret != -EAGAIN) {
 557                                 trace_iomap_dio_invalidate_fail(inode, iomi.pos,
 558                                                                 iomi.len);
 559                                 ret = -ENOTBLK;
 560                         }
 561                         goto out_free_dio;
 562                 }
 563
 564                 if (!wait_for_completion && !inode->i_sb->s_dio_done_wq) {
 565                         ret = sb_init_dio_done_wq(inode->i_sb);
 566                         if (ret < 0)
 567                                 goto out_free_dio;
 568                 }
 569         }
 570
 571         inode_dio_begin(inode);
 572
 573         blk_start_plug(&plug);
 574         while ((ret = iomap_iter(&iomi, ops)) > 0) {
 575                 iomi.processed = iomap_dio_iter(&iomi, dio);
 576
 577                 /*
 578                  * We can only poll for single bio I/Os.
 579                  */
 580                 iocb->ki_flags &= ~IOCB_HIPRI;
 581         }
 582
 583         blk_finish_plug(&plug);
 584
 585         /*
 586          * We only report that we've read data up to i_size.
 587          * Revert iter to a state corresponding to that as some callers (such
 588          * as the splice code) rely on it.
 589          */
 590         if (iov_iter_rw(iter) == READ && iomi.pos >= dio->i_size)
 591                 iov_iter_revert(iter, iomi.pos - dio->i_size);
 592
 593         if (ret == -EFAULT && dio->size && (dio_flags & IOMAP_DIO_PARTIAL)) {
 594                 if (!(iocb->ki_flags & IOCB_NOWAIT))
 595                         wait_for_completion = true;
 596                 ret = 0;
 597         }
 598
 599         /* magic error code to fall back to buffered I/O */
 600         if (ret == -ENOTBLK) {
 601                 wait_for_completion = true;
 602                 ret = 0;
 603         }
 604         if (ret < 0)
 605                 iomap_dio_set_error(dio, ret);
 606
 607         /*
 608          * If all the writes we issued were FUA, we don't need to flush the
 609          * cache on IO completion. Clear the sync flag for this case.
 610          */
 611         if (dio->flags & IOMAP_DIO_WRITE_FUA)
 612                 dio->flags &= ~IOMAP_DIO_NEED_SYNC;
 613
 614         WRITE_ONCE(iocb->private, dio->submit.poll_bio);
 615
 616         /*
 617          * We are about to drop our additional submission reference, which
 618          * might be the last reference to the dio.  There are three different
 619          * ways we can progress here:
 620          *
 621          *  (a) If this is the last reference we will always complete and free
 622          *      the dio ourselves.
 623          *  (b) If this is not the last reference, and we serve an asynchronous
 624          *      iocb, we must never touch the dio after the decrement, the
 625          *      I/O completion handler will complete and free it.
 626          *  (c) If this is not the last reference, but we serve a synchronous
 627          *      iocb, the I/O completion handler will wake us up on the drop
 628          *      of the final reference, and we will complete and free it here
 629          *      after we got woken by the I/O completion handler.
 630          */
 631         dio->wait_for_completion = wait_for_completion;
 632         if (!atomic_dec_and_test(&dio->ref)) {
 633                 if (!wait_for_completion) {
 634                         trace_iomap_dio_rw_queued(inode, iomi.pos, iomi.len);
 635                         return ERR_PTR(-EIOCBQUEUED);
 636                 }
 637
 638                 for (;;) {
 639                         set_current_state(TASK_UNINTERRUPTIBLE);
 640                         if (!READ_ONCE(dio->submit.waiter))
 641                                 break;
 642
 643                         blk_io_schedule();
 644                 }
 645                 __set_current_state(TASK_RUNNING);
 646         }
 647
 648         return dio;
 649
 650 out_free_dio:
 651         kfree(dio);
 652         if (ret)
 653                 return ERR_PTR(ret);
 654         return NULL;
 655 }
 656 EXPORT_SYMBOL_GPL(__iomap_dio_rw);
 657
 658 ssize_t
 659 iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 660                 const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
 661                 unsigned int dio_flags, void *private, size_t done_before)
 662 {
 663         struct iomap_dio *dio;
 664
 665         dio = __iomap_dio_rw(iocb, iter, ops, dops, dio_flags, private,
 666                              done_before);
 667         if (IS_ERR_OR_NULL(dio))
 668                 return PTR_ERR_OR_ZERO(dio);
 669         return iomap_dio_complete(dio);
 670 }
 671 EXPORT_SYMBOL_GPL(iomap_dio_rw);