direct-io.c

   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * fs/direct-io.c
   4 *
   5 * Copyright (C) 2002, Linus Torvalds.
   6 *
   7 * O_DIRECT
   8 *
   9 * 04Jul2002	Andrew Morton
  10 *		Initial version
  11 * 11Sep2002	janetinc@us.ibm.com
  12 * 		added readv/writev support.
  13 * 29Oct2002	Andrew Morton
  14 *		rewrote bio_add_page() support.
  15 * 30Oct2002	pbadari@us.ibm.com
  16 *		added support for non-aligned IO.
  17 * 06Nov2002	pbadari@us.ibm.com
  18 *		added asynchronous IO support.
  19 * 21Jul2003	nathans@sgi.com
  20 *		added IO completion notifier.
  21 */
  22
  23#include <linux/kernel.h>
  24#include <linux/module.h>
  25#include <linux/types.h>
  26#include <linux/fs.h>
  27#include <linux/mm.h>
  28#include <linux/slab.h>
  29#include <linux/highmem.h>
  30#include <linux/pagemap.h>
  31#include <linux/task_io_accounting_ops.h>
  32#include <linux/bio.h>
  33#include <linux/wait.h>
  34#include <linux/err.h>
  35#include <linux/blkdev.h>
  36#include <linux/buffer_head.h>
  37#include <linux/rwsem.h>
  38#include <linux/uio.h>
  39#include <linux/atomic.h>
  40
  41#include "internal.h"
  42
  43/*
  44 * How many user pages to map in one call to iov_iter_extract_pages().  This
  45 * determines the size of a structure in the slab cache
  46 */
  47#define DIO_PAGES	64
  48
  49/*
  50 * Flags for dio_complete()
  51 */
  52#define DIO_COMPLETE_ASYNC		0x01	/* This is async IO */
  53#define DIO_COMPLETE_INVALIDATE		0x02	/* Can invalidate pages */
  54
  55/*
  56 * This code generally works in units of "dio_blocks".  A dio_block is
  57 * somewhere between the hard sector size and the filesystem block size.  it
  58 * is determined on a per-invocation basis.   When talking to the filesystem
  59 * we need to convert dio_blocks to fs_blocks by scaling the dio_block quantity
  60 * down by dio->blkfactor.  Similarly, fs-blocksize quantities are converted
  61 * to bio_block quantities by shifting left by blkfactor.
  62 *
  63 * If blkfactor is zero then the user's request was aligned to the filesystem's
  64 * blocksize.
  65 */
  66
  67/* dio_state only used in the submission path */
  68
  69struct dio_submit {
  70	struct bio *bio;		/* bio under assembly */
  71	unsigned blkbits;		/* doesn't change */
  72	unsigned blkfactor;		/* When we're using an alignment which
  73					   is finer than the filesystem's soft
  74					   blocksize, this specifies how much
  75					   finer.  blkfactor=2 means 1/4-block
  76					   alignment.  Does not change */
  77	unsigned start_zero_done;	/* flag: sub-blocksize zeroing has
  78					   been performed at the start of a
  79					   write */
  80	int pages_in_io;		/* approximate total IO pages */
  81	sector_t block_in_file;		/* Current offset into the underlying
  82					   file in dio_block units. */
  83	unsigned blocks_available;	/* At block_in_file.  changes */
  84	int reap_counter;		/* rate limit reaping */
  85	sector_t final_block_in_request;/* doesn't change */
  86	int boundary;			/* prev block is at a boundary */
  87	get_block_t *get_block;		/* block mapping function */
  88
  89	loff_t logical_offset_in_bio;	/* current first logical block in bio */
  90	sector_t final_block_in_bio;	/* current final block in bio + 1 */
  91	sector_t next_block_for_io;	/* next block to be put under IO,
  92					   in dio_blocks units */
  93
  94	/*
  95	 * Deferred addition of a page to the dio.  These variables are
  96	 * private to dio_send_cur_page(), submit_page_section() and
  97	 * dio_bio_add_page().
  98	 */
  99	struct page *cur_page;		/* The page */
 100	unsigned cur_page_offset;	/* Offset into it, in bytes */
 101	unsigned cur_page_len;		/* Nr of bytes at cur_page_offset */
 102	sector_t cur_page_block;	/* Where it starts */
 103	loff_t cur_page_fs_offset;	/* Offset in file */
 104
 105	struct iov_iter *iter;
 106	/*
 107	 * Page queue.  These variables belong to dio_refill_pages() and
 108	 * dio_get_page().
 109	 */
 110	unsigned head;			/* next page to process */
 111	unsigned tail;			/* last valid page + 1 */
 112	size_t from, to;
 113};
 114
 115/* dio_state communicated between submission path and end_io */
 116struct dio {
 117	int flags;			/* doesn't change */
 118	blk_opf_t opf;			/* request operation type and flags */
 119	struct gendisk *bio_disk;
 120	struct inode *inode;
 121	loff_t i_size;			/* i_size when submitted */
 122	dio_iodone_t *end_io;		/* IO completion function */
 123	bool is_pinned;			/* T if we have pins on the pages */
 124
 125	void *private;			/* copy from map_bh.b_private */
 126
 127	/* BIO completion state */
 128	spinlock_t bio_lock;		/* protects BIO fields below */
 129	int page_errors;		/* err from iov_iter_extract_pages() */
 130	int is_async;			/* is IO async ? */
 131	bool defer_completion;		/* defer AIO completion to workqueue? */
 132	bool should_dirty;		/* if pages should be dirtied */
 133	int io_error;			/* IO error in completion path */
 134	unsigned long refcount;		/* direct_io_worker() and bios */
 135	struct bio *bio_list;		/* singly linked via bi_private */
 136	struct task_struct *waiter;	/* waiting task (NULL if none) */
 137
 138	/* AIO related stuff */
 139	struct kiocb *iocb;		/* kiocb */
 140	ssize_t result;                 /* IO result */
 141
 142	/*
 143	 * pages[] (and any fields placed after it) are not zeroed out at
 144	 * allocation time.  Don't add new fields after pages[] unless you
 145	 * wish that they not be zeroed.
 146	 */
 147	union {
 148		struct page *pages[DIO_PAGES];	/* page buffer */
 149		struct work_struct complete_work;/* deferred AIO completion */
 150	};
 151} ____cacheline_aligned_in_smp;
 152
 153static struct kmem_cache *dio_cache __ro_after_init;
 154
 155/*
 156 * How many pages are in the queue?
 157 */
 158static inline unsigned dio_pages_present(struct dio_submit *sdio)
 159{
 160	return sdio->tail - sdio->head;
 161}
 162
 163/*
 164 * Go grab and pin some userspace pages.   Typically we'll get 64 at a time.
 165 */
 166static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
 167{
 168	struct page **pages = dio->pages;
 169	const enum req_op dio_op = dio->opf & REQ_OP_MASK;
 170	ssize_t ret;
 171
 172	ret = iov_iter_extract_pages(sdio->iter, &pages, LONG_MAX,
 173				     DIO_PAGES, 0, &sdio->from);
 174
 175	if (ret < 0 && sdio->blocks_available && dio_op == REQ_OP_WRITE) {
 176		/*
 177		 * A memory fault, but the filesystem has some outstanding
 178		 * mapped blocks.  We need to use those blocks up to avoid
 179		 * leaking stale data in the file.
 180		 */
 181		if (dio->page_errors == 0)
 182			dio->page_errors = ret;
 183		dio->pages[0] = ZERO_PAGE(0);
 184		sdio->head = 0;
 185		sdio->tail = 1;
 186		sdio->from = 0;
 187		sdio->to = PAGE_SIZE;
 188		return 0;
 189	}
 190
 191	if (ret >= 0) {
 192		ret += sdio->from;
 193		sdio->head = 0;
 194		sdio->tail = (ret + PAGE_SIZE - 1) / PAGE_SIZE;
 195		sdio->to = ((ret - 1) & (PAGE_SIZE - 1)) + 1;
 196		return 0;
 197	}
 198	return ret;	
 199}
 200
 201/*
 202 * Get another userspace page.  Returns an ERR_PTR on error.  Pages are
 203 * buffered inside the dio so that we can call iov_iter_extract_pages()
 204 * against a decent number of pages, less frequently.  To provide nicer use of
 205 * the L1 cache.
 206 */
 207static inline struct page *dio_get_page(struct dio *dio,
 208					struct dio_submit *sdio)
 209{
 210	if (dio_pages_present(sdio) == 0) {
 211		int ret;
 212
 213		ret = dio_refill_pages(dio, sdio);
 214		if (ret)
 215			return ERR_PTR(ret);
 216		BUG_ON(dio_pages_present(sdio) == 0);
 217	}
 218	return dio->pages[sdio->head];
 219}
 220
 221static void dio_pin_page(struct dio *dio, struct page *page)
 222{
 223	if (dio->is_pinned)
 224		folio_add_pin(page_folio(page));
 225}
 226
 227static void dio_unpin_page(struct dio *dio, struct page *page)
 228{
 229	if (dio->is_pinned)
 230		unpin_user_page(page);
 231}
 232
 233/*
 234 * dio_complete() - called when all DIO BIO I/O has been completed
 235 *
 236 * This drops i_dio_count, lets interested parties know that a DIO operation
 237 * has completed, and calculates the resulting return code for the operation.
 238 *
 239 * It lets the filesystem know if it registered an interest earlier via
 240 * get_block.  Pass the private field of the map buffer_head so that
 241 * filesystems can use it to hold additional state between get_block calls and
 242 * dio_complete.
 243 */
 244static ssize_t dio_complete(struct dio *dio, ssize_t ret, unsigned int flags)
 245{
 246	const enum req_op dio_op = dio->opf & REQ_OP_MASK;
 247	loff_t offset = dio->iocb->ki_pos;
 248	ssize_t transferred = 0;
 249	int err;
 250
 251	/*
 252	 * AIO submission can race with bio completion to get here while
 253	 * expecting to have the last io completed by bio completion.
 254	 * In that case -EIOCBQUEUED is in fact not an error we want
 255	 * to preserve through this call.
 256	 */
 257	if (ret == -EIOCBQUEUED)
 258		ret = 0;
 259
 260	if (dio->result) {
 261		transferred = dio->result;
 262
 263		/* Check for short read case */
 264		if (dio_op == REQ_OP_READ &&
 265		    ((offset + transferred) > dio->i_size))
 266			transferred = dio->i_size - offset;
 267		/* ignore EFAULT if some IO has been done */
 268		if (unlikely(ret == -EFAULT) && transferred)
 269			ret = 0;
 270	}
 271
 272	if (ret == 0)
 273		ret = dio->page_errors;
 274	if (ret == 0)
 275		ret = dio->io_error;
 276	if (ret == 0)
 277		ret = transferred;
 278
 279	if (dio->end_io) {
 280		// XXX: ki_pos??
 281		err = dio->end_io(dio->iocb, offset, ret, dio->private);
 282		if (err)
 283			ret = err;
 284	}
 285
 286	/*
 287	 * Try again to invalidate clean pages which might have been cached by
 288	 * non-direct readahead, or faulted in by get_user_pages() if the source
 289	 * of the write was an mmap'ed region of the file we're writing.  Either
 290	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
 291	 * this invalidation fails, tough, the write still worked...
 292	 *
 293	 * And this page cache invalidation has to be after dio->end_io(), as
 294	 * some filesystems convert unwritten extents to real allocations in
 295	 * end_io() when necessary, otherwise a racing buffer read would cache
 296	 * zeros from unwritten extents.
 297	 */
 298	if (flags & DIO_COMPLETE_INVALIDATE &&
 299	    ret > 0 && dio_op == REQ_OP_WRITE)
 300		kiocb_invalidate_post_direct_write(dio->iocb, ret);
 301
 302	inode_dio_end(dio->inode);
 303
 304	if (flags & DIO_COMPLETE_ASYNC) {
 305		/*
 306		 * generic_write_sync expects ki_pos to have been updated
 307		 * already, but the submission path only does this for
 308		 * synchronous I/O.
 309		 */
 310		dio->iocb->ki_pos += transferred;
 311
 312		if (ret > 0 && dio_op == REQ_OP_WRITE)
 313			ret = generic_write_sync(dio->iocb, ret);
 314		dio->iocb->ki_complete(dio->iocb, ret);
 315	}
 316
 317	kmem_cache_free(dio_cache, dio);
 318	return ret;
 319}
 320
 321static void dio_aio_complete_work(struct work_struct *work)
 322{
 323	struct dio *dio = container_of(work, struct dio, complete_work);
 324
 325	dio_complete(dio, 0, DIO_COMPLETE_ASYNC | DIO_COMPLETE_INVALIDATE);
 326}
 327
 328static blk_status_t dio_bio_complete(struct dio *dio, struct bio *bio);
 329
 330/*
 331 * Asynchronous IO callback. 
 332 */
 333static void dio_bio_end_aio(struct bio *bio)
 334{
 335	struct dio *dio = bio->bi_private;
 336	const enum req_op dio_op = dio->opf & REQ_OP_MASK;
 337	unsigned long remaining;
 338	unsigned long flags;
 339	bool defer_completion = false;
 340
 341	/* cleanup the bio */
 342	dio_bio_complete(dio, bio);
 343
 344	spin_lock_irqsave(&dio->bio_lock, flags);
 345	remaining = --dio->refcount;
 346	if (remaining == 1 && dio->waiter)
 347		wake_up_process(dio->waiter);
 348	spin_unlock_irqrestore(&dio->bio_lock, flags);
 349
 350	if (remaining == 0) {
 351		/*
 352		 * Defer completion when defer_completion is set or
 353		 * when the inode has pages mapped and this is AIO write.
 354		 * We need to invalidate those pages because there is a
 355		 * chance they contain stale data in the case buffered IO
 356		 * went in between AIO submission and completion into the
 357		 * same region.
 358		 */
 359		if (dio->result)
 360			defer_completion = dio->defer_completion ||
 361					   (dio_op == REQ_OP_WRITE &&
 362					    dio->inode->i_mapping->nrpages);
 363		if (defer_completion) {
 364			INIT_WORK(&dio->complete_work, dio_aio_complete_work);
 365			queue_work(dio->inode->i_sb->s_dio_done_wq,
 366				   &dio->complete_work);
 367		} else {
 368			dio_complete(dio, 0, DIO_COMPLETE_ASYNC);
 369		}
 370	}
 371}
 372
 373/*
 374 * The BIO completion handler simply queues the BIO up for the process-context
 375 * handler.
 376 *
 377 * During I/O bi_private points at the dio.  After I/O, bi_private is used to
 378 * implement a singly-linked list of completed BIOs, at dio->bio_list.
 379 */
 380static void dio_bio_end_io(struct bio *bio)
 381{
 382	struct dio *dio = bio->bi_private;
 383	unsigned long flags;
 384
 385	spin_lock_irqsave(&dio->bio_lock, flags);
 386	bio->bi_private = dio->bio_list;
 387	dio->bio_list = bio;
 388	if (--dio->refcount == 1 && dio->waiter)
 389		wake_up_process(dio->waiter);
 390	spin_unlock_irqrestore(&dio->bio_lock, flags);
 391}
 392
 393static inline void
 394dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
 395	      struct block_device *bdev,
 396	      sector_t first_sector, int nr_vecs)
 397{
 398	struct bio *bio;
 399
 400	/*
 401	 * bio_alloc() is guaranteed to return a bio when allowed to sleep and
 402	 * we request a valid number of vectors.
 403	 */
 404	bio = bio_alloc(bdev, nr_vecs, dio->opf, GFP_KERNEL);
 405	bio->bi_iter.bi_sector = first_sector;
 406	if (dio->is_async)
 407		bio->bi_end_io = dio_bio_end_aio;
 408	else
 409		bio->bi_end_io = dio_bio_end_io;
 410	if (dio->is_pinned)
 411		bio_set_flag(bio, BIO_PAGE_PINNED);
 412	bio->bi_write_hint = file_inode(dio->iocb->ki_filp)->i_write_hint;
 413
 414	sdio->bio = bio;
 415	sdio->logical_offset_in_bio = sdio->cur_page_fs_offset;
 416}
 417
 418/*
 419 * In the AIO read case we speculatively dirty the pages before starting IO.
 420 * During IO completion, any of these pages which happen to have been written
 421 * back will be redirtied by bio_check_pages_dirty().
 422 *
 423 * bios hold a dio reference between submit_bio and ->end_io.
 424 */
 425static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
 426{
 427	const enum req_op dio_op = dio->opf & REQ_OP_MASK;
 428	struct bio *bio = sdio->bio;
 429	unsigned long flags;
 430
 431	bio->bi_private = dio;
 432
 433	spin_lock_irqsave(&dio->bio_lock, flags);
 434	dio->refcount++;
 435	spin_unlock_irqrestore(&dio->bio_lock, flags);
 436
 437	if (dio->is_async && dio_op == REQ_OP_READ && dio->should_dirty)
 438		bio_set_pages_dirty(bio);
 439
 440	dio->bio_disk = bio->bi_bdev->bd_disk;
 441
 442	submit_bio(bio);
 443
 444	sdio->bio = NULL;
 445	sdio->boundary = 0;
 446	sdio->logical_offset_in_bio = 0;
 447}
 448
 449/*
 450 * Release any resources in case of a failure
 451 */
 452static inline void dio_cleanup(struct dio *dio, struct dio_submit *sdio)
 453{
 454	if (dio->is_pinned)
 455		unpin_user_pages(dio->pages + sdio->head,
 456				 sdio->tail - sdio->head);
 457	sdio->head = sdio->tail;
 458}
 459
 460/*
 461 * Wait for the next BIO to complete.  Remove it and return it.  NULL is
 462 * returned once all BIOs have been completed.  This must only be called once
 463 * all bios have been issued so that dio->refcount can only decrease.  This
 464 * requires that the caller hold a reference on the dio.
 465 */
 466static struct bio *dio_await_one(struct dio *dio)
 467{
 468	unsigned long flags;
 469	struct bio *bio = NULL;
 470
 471	spin_lock_irqsave(&dio->bio_lock, flags);
 472
 473	/*
 474	 * Wait as long as the list is empty and there are bios in flight.  bio
 475	 * completion drops the count, maybe adds to the list, and wakes while
 476	 * holding the bio_lock so we don't need set_current_state()'s barrier
 477	 * and can call it after testing our condition.
 478	 */
 479	while (dio->refcount > 1 && dio->bio_list == NULL) {
 480		__set_current_state(TASK_UNINTERRUPTIBLE);
 481		dio->waiter = current;
 482		spin_unlock_irqrestore(&dio->bio_lock, flags);
 483		blk_io_schedule();
 484		/* wake up sets us TASK_RUNNING */
 485		spin_lock_irqsave(&dio->bio_lock, flags);
 486		dio->waiter = NULL;
 487	}
 488	if (dio->bio_list) {
 489		bio = dio->bio_list;
 490		dio->bio_list = bio->bi_private;
 491	}
 492	spin_unlock_irqrestore(&dio->bio_lock, flags);
 493	return bio;
 494}
 495
 496/*
 497 * Process one completed BIO.  No locks are held.
 498 */
 499static blk_status_t dio_bio_complete(struct dio *dio, struct bio *bio)
 500{
 501	blk_status_t err = bio->bi_status;
 502	const enum req_op dio_op = dio->opf & REQ_OP_MASK;
 503	bool should_dirty = dio_op == REQ_OP_READ && dio->should_dirty;
 504
 505	if (err) {
 506		if (err == BLK_STS_AGAIN && (bio->bi_opf & REQ_NOWAIT))
 507			dio->io_error = -EAGAIN;
 508		else
 509			dio->io_error = -EIO;
 510	}
 511
 512	if (dio->is_async && should_dirty) {
 513		bio_check_pages_dirty(bio);	/* transfers ownership */
 514	} else {
 515		bio_release_pages(bio, should_dirty);
 516		bio_put(bio);
 517	}
 518	return err;
 519}
 520
 521/*
 522 * Wait on and process all in-flight BIOs.  This must only be called once
 523 * all bios have been issued so that the refcount can only decrease.
 524 * This just waits for all bios to make it through dio_bio_complete.  IO
 525 * errors are propagated through dio->io_error and should be propagated via
 526 * dio_complete().
 527 */
 528static void dio_await_completion(struct dio *dio)
 529{
 530	struct bio *bio;
 531	do {
 532		bio = dio_await_one(dio);
 533		if (bio)
 534			dio_bio_complete(dio, bio);
 535	} while (bio);
 536}
 537
 538/*
 539 * A really large O_DIRECT read or write can generate a lot of BIOs.  So
 540 * to keep the memory consumption sane we periodically reap any completed BIOs
 541 * during the BIO generation phase.
 542 *
 543 * This also helps to limit the peak amount of pinned userspace memory.
 544 */
 545static inline int dio_bio_reap(struct dio *dio, struct dio_submit *sdio)
 546{
 547	int ret = 0;
 548
 549	if (sdio->reap_counter++ >= 64) {
 550		while (dio->bio_list) {
 551			unsigned long flags;
 552			struct bio *bio;
 553			int ret2;
 554
 555			spin_lock_irqsave(&dio->bio_lock, flags);
 556			bio = dio->bio_list;
 557			dio->bio_list = bio->bi_private;
 558			spin_unlock_irqrestore(&dio->bio_lock, flags);
 559			ret2 = blk_status_to_errno(dio_bio_complete(dio, bio));
 560			if (ret == 0)
 561				ret = ret2;
 562		}
 563		sdio->reap_counter = 0;
 564	}
 565	return ret;
 566}
 567
 568static int dio_set_defer_completion(struct dio *dio)
 569{
 570	struct super_block *sb = dio->inode->i_sb;
 571
 572	if (dio->defer_completion)
 573		return 0;
 574	dio->defer_completion = true;
 575	if (!sb->s_dio_done_wq)
 576		return sb_init_dio_done_wq(sb);
 577	return 0;
 578}
 579
 580/*
 581 * Call into the fs to map some more disk blocks.  We record the current number
 582 * of available blocks at sdio->blocks_available.  These are in units of the
 583 * fs blocksize, i_blocksize(inode).
 584 *
 585 * The fs is allowed to map lots of blocks at once.  If it wants to do that,
 586 * it uses the passed inode-relative block number as the file offset, as usual.
 587 *
 588 * get_block() is passed the number of i_blkbits-sized blocks which direct_io
 589 * has remaining to do.  The fs should not map more than this number of blocks.
 590 *
 591 * If the fs has mapped a lot of blocks, it should populate bh->b_size to
 592 * indicate how much contiguous disk space has been made available at
 593 * bh->b_blocknr.
 594 *
 595 * If *any* of the mapped blocks are new, then the fs must set buffer_new().
 596 * This isn't very efficient...
 597 *
 598 * In the case of filesystem holes: the fs may return an arbitrarily-large
 599 * hole by returning an appropriate value in b_size and by clearing
 600 * buffer_mapped().  However the direct-io code will only process holes one
 601 * block at a time - it will repeatedly call get_block() as it walks the hole.
 602 */
 603static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
 604			   struct buffer_head *map_bh)
 605{
 606	const enum req_op dio_op = dio->opf & REQ_OP_MASK;
 607	int ret;
 608	sector_t fs_startblk;	/* Into file, in filesystem-sized blocks */
 609	sector_t fs_endblk;	/* Into file, in filesystem-sized blocks */
 610	unsigned long fs_count;	/* Number of filesystem-sized blocks */
 611	int create;
 612	unsigned int i_blkbits = sdio->blkbits + sdio->blkfactor;
 613	loff_t i_size;
 614
 615	/*
 616	 * If there was a memory error and we've overwritten all the
 617	 * mapped blocks then we can now return that memory error
 618	 */
 619	ret = dio->page_errors;
 620	if (ret == 0) {
 621		BUG_ON(sdio->block_in_file >= sdio->final_block_in_request);
 622		fs_startblk = sdio->block_in_file >> sdio->blkfactor;
 623		fs_endblk = (sdio->final_block_in_request - 1) >>
 624					sdio->blkfactor;
 625		fs_count = fs_endblk - fs_startblk + 1;
 626
 627		map_bh->b_state = 0;
 628		map_bh->b_size = fs_count << i_blkbits;
 629
 630		/*
 631		 * For writes that could fill holes inside i_size on a
 632		 * DIO_SKIP_HOLES filesystem we forbid block creations: only
 633		 * overwrites are permitted. We will return early to the caller
 634		 * once we see an unmapped buffer head returned, and the caller
 635		 * will fall back to buffered I/O.
 636		 *
 637		 * Otherwise the decision is left to the get_blocks method,
 638		 * which may decide to handle it or also return an unmapped
 639		 * buffer head.
 640		 */
 641		create = dio_op == REQ_OP_WRITE;
 642		if (dio->flags & DIO_SKIP_HOLES) {
 643			i_size = i_size_read(dio->inode);
 644			if (i_size && fs_startblk <= (i_size - 1) >> i_blkbits)
 645				create = 0;
 646		}
 647
 648		ret = (*sdio->get_block)(dio->inode, fs_startblk,
 649						map_bh, create);
 650
 651		/* Store for completion */
 652		dio->private = map_bh->b_private;
 653
 654		if (ret == 0 && buffer_defer_completion(map_bh))
 655			ret = dio_set_defer_completion(dio);
 656	}
 657	return ret;
 658}
 659
 660/*
 661 * There is no bio.  Make one now.
 662 */
 663static inline int dio_new_bio(struct dio *dio, struct dio_submit *sdio,
 664		sector_t start_sector, struct buffer_head *map_bh)
 665{
 666	sector_t sector;
 667	int ret, nr_pages;
 668
 669	ret = dio_bio_reap(dio, sdio);
 670	if (ret)
 671		goto out;
 672	sector = start_sector << (sdio->blkbits - 9);
 673	nr_pages = bio_max_segs(sdio->pages_in_io);
 674	BUG_ON(nr_pages <= 0);
 675	dio_bio_alloc(dio, sdio, map_bh->b_bdev, sector, nr_pages);
 676	sdio->boundary = 0;
 677out:
 678	return ret;
 679}
 680
 681/*
 682 * Attempt to put the current chunk of 'cur_page' into the current BIO.  If
 683 * that was successful then update final_block_in_bio and take a ref against
 684 * the just-added page.
 685 *
 686 * Return zero on success.  Non-zero means the caller needs to start a new BIO.
 687 */
 688static inline int dio_bio_add_page(struct dio *dio, struct dio_submit *sdio)
 689{
 690	int ret;
 691
 692	ret = bio_add_page(sdio->bio, sdio->cur_page,
 693			sdio->cur_page_len, sdio->cur_page_offset);
 694	if (ret == sdio->cur_page_len) {
 695		/*
 696		 * Decrement count only, if we are done with this page
 697		 */
 698		if ((sdio->cur_page_len + sdio->cur_page_offset) == PAGE_SIZE)
 699			sdio->pages_in_io--;
 700		dio_pin_page(dio, sdio->cur_page);
 701		sdio->final_block_in_bio = sdio->cur_page_block +
 702			(sdio->cur_page_len >> sdio->blkbits);
 703		ret = 0;
 704	} else {
 705		ret = 1;
 706	}
 707	return ret;
 708}
 709		
 710/*
 711 * Put cur_page under IO.  The section of cur_page which is described by
 712 * cur_page_offset,cur_page_len is put into a BIO.  The section of cur_page
 713 * starts on-disk at cur_page_block.
 714 *
 715 * We take a ref against the page here (on behalf of its presence in the bio).
 716 *
 717 * The caller of this function is responsible for removing cur_page from the
 718 * dio, and for dropping the refcount which came from that presence.
 719 */
 720static inline int dio_send_cur_page(struct dio *dio, struct dio_submit *sdio,
 721		struct buffer_head *map_bh)
 722{
 723	int ret = 0;
 724
 725	if (sdio->bio) {
 726		loff_t cur_offset = sdio->cur_page_fs_offset;
 727		loff_t bio_next_offset = sdio->logical_offset_in_bio +
 728			sdio->bio->bi_iter.bi_size;
 729
 730		/*
 731		 * See whether this new request is contiguous with the old.
 732		 *
 733		 * Btrfs cannot handle having logically non-contiguous requests
 734		 * submitted.  For example if you have
 735		 *
 736		 * Logical:  [0-4095][HOLE][8192-12287]
 737		 * Physical: [0-4095]      [4096-8191]
 738		 *
 739		 * We cannot submit those pages together as one BIO.  So if our
 740		 * current logical offset in the file does not equal what would
 741		 * be the next logical offset in the bio, submit the bio we
 742		 * have.
 743		 */
 744		if (sdio->final_block_in_bio != sdio->cur_page_block ||
 745		    cur_offset != bio_next_offset)
 746			dio_bio_submit(dio, sdio);
 747	}
 748
 749	if (sdio->bio == NULL) {
 750		ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
 751		if (ret)
 752			goto out;
 753	}
 754
 755	if (dio_bio_add_page(dio, sdio) != 0) {
 756		dio_bio_submit(dio, sdio);
 757		ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
 758		if (ret == 0) {
 759			ret = dio_bio_add_page(dio, sdio);
 760			BUG_ON(ret != 0);
 761		}
 762	}
 763out:
 764	return ret;
 765}
 766
 767/*
 768 * An autonomous function to put a chunk of a page under deferred IO.
 769 *
 770 * The caller doesn't actually know (or care) whether this piece of page is in
 771 * a BIO, or is under IO or whatever.  We just take care of all possible 
 772 * situations here.  The separation between the logic of do_direct_IO() and
 773 * that of submit_page_section() is important for clarity.  Please don't break.
 774 *
 775 * The chunk of page starts on-disk at blocknr.
 776 *
 777 * We perform deferred IO, by recording the last-submitted page inside our
 778 * private part of the dio structure.  If possible, we just expand the IO
 779 * across that page here.
 780 *
 781 * If that doesn't work out then we put the old page into the bio and add this
 782 * page to the dio instead.
 783 */
 784static inline int
 785submit_page_section(struct dio *dio, struct dio_submit *sdio, struct page *page,
 786		    unsigned offset, unsigned len, sector_t blocknr,
 787		    struct buffer_head *map_bh)
 788{
 789	const enum req_op dio_op = dio->opf & REQ_OP_MASK;
 790	int ret = 0;
 791	int boundary = sdio->boundary;	/* dio_send_cur_page may clear it */
 792
 793	if (dio_op == REQ_OP_WRITE) {
 794		/*
 795		 * Read accounting is performed in submit_bio()
 796		 */
 797		task_io_account_write(len);
 798	}
 799
 800	/*
 801	 * Can we just grow the current page's presence in the dio?
 802	 */
 803	if (sdio->cur_page == page &&
 804	    sdio->cur_page_offset + sdio->cur_page_len == offset &&
 805	    sdio->cur_page_block +
 806	    (sdio->cur_page_len >> sdio->blkbits) == blocknr) {
 807		sdio->cur_page_len += len;
 808		goto out;
 809	}
 810
 811	/*
 812	 * If there's a deferred page already there then send it.
 813	 */
 814	if (sdio->cur_page) {
 815		ret = dio_send_cur_page(dio, sdio, map_bh);
 816		dio_unpin_page(dio, sdio->cur_page);
 817		sdio->cur_page = NULL;
 818		if (ret)
 819			return ret;
 820	}
 821
 822	dio_pin_page(dio, page);		/* It is in dio */
 823	sdio->cur_page = page;
 824	sdio->cur_page_offset = offset;
 825	sdio->cur_page_len = len;
 826	sdio->cur_page_block = blocknr;
 827	sdio->cur_page_fs_offset = sdio->block_in_file << sdio->blkbits;
 828out:
 829	/*
 830	 * If boundary then we want to schedule the IO now to
 831	 * avoid metadata seeks.
 832	 */
 833	if (boundary) {
 834		ret = dio_send_cur_page(dio, sdio, map_bh);
 835		if (sdio->bio)
 836			dio_bio_submit(dio, sdio);
 837		dio_unpin_page(dio, sdio->cur_page);
 838		sdio->cur_page = NULL;
 839	}
 840	return ret;
 841}
 842
 843/*
 844 * If we are not writing the entire block and get_block() allocated
 845 * the block for us, we need to fill-in the unused portion of the
 846 * block with zeros. This happens only if user-buffer, fileoffset or
 847 * io length is not filesystem block-size multiple.
 848 *
 849 * `end' is zero if we're doing the start of the IO, 1 at the end of the
 850 * IO.
 851 */
 852static inline void dio_zero_block(struct dio *dio, struct dio_submit *sdio,
 853		int end, struct buffer_head *map_bh)
 854{
 855	unsigned dio_blocks_per_fs_block;
 856	unsigned this_chunk_blocks;	/* In dio_blocks */
 857	unsigned this_chunk_bytes;
 858	struct page *page;
 859
 860	sdio->start_zero_done = 1;
 861	if (!sdio->blkfactor || !buffer_new(map_bh))
 862		return;
 863
 864	dio_blocks_per_fs_block = 1 << sdio->blkfactor;
 865	this_chunk_blocks = sdio->block_in_file & (dio_blocks_per_fs_block - 1);
 866
 867	if (!this_chunk_blocks)
 868		return;
 869
 870	/*
 871	 * We need to zero out part of an fs block.  It is either at the
 872	 * beginning or the end of the fs block.
 873	 */
 874	if (end) 
 875		this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks;
 876
 877	this_chunk_bytes = this_chunk_blocks << sdio->blkbits;
 878
 879	page = ZERO_PAGE(0);
 880	if (submit_page_section(dio, sdio, page, 0, this_chunk_bytes,
 881				sdio->next_block_for_io, map_bh))
 882		return;
 883
 884	sdio->next_block_for_io += this_chunk_blocks;
 885}
 886
 887/*
 888 * Walk the user pages, and the file, mapping blocks to disk and generating
 889 * a sequence of (page,offset,len,block) mappings.  These mappings are injected
 890 * into submit_page_section(), which takes care of the next stage of submission
 891 *
 892 * Direct IO against a blockdev is different from a file.  Because we can
 893 * happily perform page-sized but 512-byte aligned IOs.  It is important that
 894 * blockdev IO be able to have fine alignment and large sizes.
 895 *
 896 * So what we do is to permit the ->get_block function to populate bh.b_size
 897 * with the size of IO which is permitted at this offset and this i_blkbits.
 898 *
 899 * For best results, the blockdev should be set up with 512-byte i_blkbits and
 900 * it should set b_size to PAGE_SIZE or more inside get_block().  This gives
 901 * fine alignment but still allows this function to work in PAGE_SIZE units.
 902 */
 903static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
 904			struct buffer_head *map_bh)
 905{
 906	const enum req_op dio_op = dio->opf & REQ_OP_MASK;
 907	const unsigned blkbits = sdio->blkbits;
 908	const unsigned i_blkbits = blkbits + sdio->blkfactor;
 909	int ret = 0;
 910
 911	while (sdio->block_in_file < sdio->final_block_in_request) {
 912		struct page *page;
 913		size_t from, to;
 914
 915		page = dio_get_page(dio, sdio);
 916		if (IS_ERR(page)) {
 917			ret = PTR_ERR(page);
 918			goto out;
 919		}
 920		from = sdio->head ? 0 : sdio->from;
 921		to = (sdio->head == sdio->tail - 1) ? sdio->to : PAGE_SIZE;
 922		sdio->head++;
 923
 924		while (from < to) {
 925			unsigned this_chunk_bytes;	/* # of bytes mapped */
 926			unsigned this_chunk_blocks;	/* # of blocks */
 927			unsigned u;
 928
 929			if (sdio->blocks_available == 0) {
 930				/*
 931				 * Need to go and map some more disk
 932				 */
 933				unsigned long blkmask;
 934				unsigned long dio_remainder;
 935
 936				ret = get_more_blocks(dio, sdio, map_bh);
 937				if (ret) {
 938					dio_unpin_page(dio, page);
 939					goto out;
 940				}
 941				if (!buffer_mapped(map_bh))
 942					goto do_holes;
 943
 944				sdio->blocks_available =
 945						map_bh->b_size >> blkbits;
 946				sdio->next_block_for_io =
 947					map_bh->b_blocknr << sdio->blkfactor;
 948				if (buffer_new(map_bh)) {
 949					clean_bdev_aliases(
 950						map_bh->b_bdev,
 951						map_bh->b_blocknr,
 952						map_bh->b_size >> i_blkbits);
 953				}
 954
 955				if (!sdio->blkfactor)
 956					goto do_holes;
 957
 958				blkmask = (1 << sdio->blkfactor) - 1;
 959				dio_remainder = (sdio->block_in_file & blkmask);
 960
 961				/*
 962				 * If we are at the start of IO and that IO
 963				 * starts partway into a fs-block,
 964				 * dio_remainder will be non-zero.  If the IO
 965				 * is a read then we can simply advance the IO
 966				 * cursor to the first block which is to be
 967				 * read.  But if the IO is a write and the
 968				 * block was newly allocated we cannot do that;
 969				 * the start of the fs block must be zeroed out
 970				 * on-disk
 971				 */
 972				if (!buffer_new(map_bh))
 973					sdio->next_block_for_io += dio_remainder;
 974				sdio->blocks_available -= dio_remainder;
 975			}
 976do_holes:
 977			/* Handle holes */
 978			if (!buffer_mapped(map_bh)) {
 979				loff_t i_size_aligned;
 980
 981				/* AKPM: eargh, -ENOTBLK is a hack */
 982				if (dio_op == REQ_OP_WRITE) {
 983					dio_unpin_page(dio, page);
 984					return -ENOTBLK;
 985				}
 986
 987				/*
 988				 * Be sure to account for a partial block as the
 989				 * last block in the file
 990				 */
 991				i_size_aligned = ALIGN(i_size_read(dio->inode),
 992							1 << blkbits);
 993				if (sdio->block_in_file >=
 994						i_size_aligned >> blkbits) {
 995					/* We hit eof */
 996					dio_unpin_page(dio, page);
 997					goto out;
 998				}
 999				memzero_page(page, from, 1 << blkbits);
1000				sdio->block_in_file++;
1001				from += 1 << blkbits;
1002				dio->result += 1 << blkbits;
1003				goto next_block;
1004			}
1005
1006			/*
1007			 * If we're performing IO which has an alignment which
1008			 * is finer than the underlying fs, go check to see if
1009			 * we must zero out the start of this block.
1010			 */
1011			if (unlikely(sdio->blkfactor && !sdio->start_zero_done))
1012				dio_zero_block(dio, sdio, 0, map_bh);
1013
1014			/*
1015			 * Work out, in this_chunk_blocks, how much disk we
1016			 * can add to this page
1017			 */
1018			this_chunk_blocks = sdio->blocks_available;
1019			u = (to - from) >> blkbits;
1020			if (this_chunk_blocks > u)
1021				this_chunk_blocks = u;
1022			u = sdio->final_block_in_request - sdio->block_in_file;
1023			if (this_chunk_blocks > u)
1024				this_chunk_blocks = u;
1025			this_chunk_bytes = this_chunk_blocks << blkbits;
1026			BUG_ON(this_chunk_bytes == 0);
1027
1028			if (this_chunk_blocks == sdio->blocks_available)
1029				sdio->boundary = buffer_boundary(map_bh);
1030			ret = submit_page_section(dio, sdio, page,
1031						  from,
1032						  this_chunk_bytes,
1033						  sdio->next_block_for_io,
1034						  map_bh);
1035			if (ret) {
1036				dio_unpin_page(dio, page);
1037				goto out;
1038			}
1039			sdio->next_block_for_io += this_chunk_blocks;
1040
1041			sdio->block_in_file += this_chunk_blocks;
1042			from += this_chunk_bytes;
1043			dio->result += this_chunk_bytes;
1044			sdio->blocks_available -= this_chunk_blocks;
1045next_block:
1046			BUG_ON(sdio->block_in_file > sdio->final_block_in_request);
1047			if (sdio->block_in_file == sdio->final_block_in_request)
1048				break;
1049		}
1050
1051		/* Drop the pin which was taken in get_user_pages() */
1052		dio_unpin_page(dio, page);
1053	}
1054out:
1055	return ret;
1056}
1057
1058static inline int drop_refcount(struct dio *dio)
1059{
1060	int ret2;
1061	unsigned long flags;
1062
1063	/*
1064	 * Sync will always be dropping the final ref and completing the
1065	 * operation.  AIO can if it was a broken operation described above or
1066	 * in fact if all the bios race to complete before we get here.  In
1067	 * that case dio_complete() translates the EIOCBQUEUED into the proper
1068	 * return code that the caller will hand to ->complete().
1069	 *
1070	 * This is managed by the bio_lock instead of being an atomic_t so that
1071	 * completion paths can drop their ref and use the remaining count to
1072	 * decide to wake the submission path atomically.
1073	 */
1074	spin_lock_irqsave(&dio->bio_lock, flags);
1075	ret2 = --dio->refcount;
1076	spin_unlock_irqrestore(&dio->bio_lock, flags);
1077	return ret2;
1078}
1079
1080/*
1081 * This is a library function for use by filesystem drivers.
1082 *
1083 * The locking rules are governed by the flags parameter:
1084 *  - if the flags value contains DIO_LOCKING we use a fancy locking
1085 *    scheme for dumb filesystems.
1086 *    For writes this function is called under i_rwsem and returns with
1087 *    i_rwsem held, for reads, i_rwsem is not held on entry, but it is
1088 *    taken and dropped again before returning.
1089 *  - if the flags value does NOT contain DIO_LOCKING we don't use any
1090 *    internal locking but rather rely on the filesystem to synchronize
1091 *    direct I/O reads/writes versus each other and truncate.
1092 *
1093 * To help with locking against truncate we incremented the i_dio_count
1094 * counter before starting direct I/O, and decrement it once we are done.
1095 * Truncate can wait for it to reach zero to provide exclusion.  It is
1096 * expected that filesystem provide exclusion between new direct I/O
1097 * and truncates.  For DIO_LOCKING filesystems this is done by i_rwsem,
1098 * but other filesystems need to take care of this on their own.
1099 *
1100 * NOTE: if you pass "sdio" to anything by pointer make sure that function
1101 * is always inlined. Otherwise gcc is unable to split the structure into
1102 * individual fields and will generate much worse code. This is important
1103 * for the whole file.
1104 */
1105ssize_t __blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
1106		struct block_device *bdev, struct iov_iter *iter,
1107		get_block_t get_block, dio_iodone_t end_io,
1108		int flags)
1109{
1110	unsigned i_blkbits = READ_ONCE(inode->i_blkbits);
1111	unsigned blkbits = i_blkbits;
1112	unsigned blocksize_mask = (1 << blkbits) - 1;
1113	ssize_t retval = -EINVAL;
1114	const size_t count = iov_iter_count(iter);
1115	loff_t offset = iocb->ki_pos;
1116	const loff_t end = offset + count;
1117	struct dio *dio;
1118	struct dio_submit sdio = { NULL, };
1119	struct buffer_head map_bh = { 0, };
1120	struct blk_plug plug;
1121	unsigned long align = offset | iov_iter_alignment(iter);
1122
1123	/* watch out for a 0 len io from a tricksy fs */
1124	if (iov_iter_rw(iter) == READ && !count)
1125		return 0;
1126
1127	dio = kmem_cache_alloc(dio_cache, GFP_KERNEL);
1128	if (!dio)
1129		return -ENOMEM;
1130	/*
1131	 * Believe it or not, zeroing out the page array caused a .5%
1132	 * performance regression in a database benchmark.  So, we take
1133	 * care to only zero out what's needed.
1134	 */
1135	memset(dio, 0, offsetof(struct dio, pages));
1136
1137	dio->flags = flags;
1138	if (dio->flags & DIO_LOCKING && iov_iter_rw(iter) == READ) {
1139		/* will be released by direct_io_worker */
1140		inode_lock(inode);
1141	}
1142	dio->is_pinned = iov_iter_extract_will_pin(iter);
1143
1144	/* Once we sampled i_size check for reads beyond EOF */
1145	dio->i_size = i_size_read(inode);
1146	if (iov_iter_rw(iter) == READ && offset >= dio->i_size) {
1147		retval = 0;
1148		goto fail_dio;
1149	}
1150
1151	if (align & blocksize_mask) {
1152		if (bdev)
1153			blkbits = blksize_bits(bdev_logical_block_size(bdev));
1154		blocksize_mask = (1 << blkbits) - 1;
1155		if (align & blocksize_mask)
1156			goto fail_dio;
1157	}
1158
1159	if (dio->flags & DIO_LOCKING && iov_iter_rw(iter) == READ) {
1160		struct address_space *mapping = iocb->ki_filp->f_mapping;
1161
1162		retval = filemap_write_and_wait_range(mapping, offset, end - 1);
1163		if (retval)
1164			goto fail_dio;
1165	}
1166
1167	/*
1168	 * For file extending writes updating i_size before data writeouts
1169	 * complete can expose uninitialized blocks in dumb filesystems.
1170	 * In that case we need to wait for I/O completion even if asked
1171	 * for an asynchronous write.
1172	 */
1173	if (is_sync_kiocb(iocb))
1174		dio->is_async = false;
1175	else if (iov_iter_rw(iter) == WRITE && end > i_size_read(inode))
1176		dio->is_async = false;
1177	else
1178		dio->is_async = true;
1179
1180	dio->inode = inode;
1181	if (iov_iter_rw(iter) == WRITE) {
1182		dio->opf = REQ_OP_WRITE | REQ_SYNC | REQ_IDLE;
1183		if (iocb->ki_flags & IOCB_NOWAIT)
1184			dio->opf |= REQ_NOWAIT;
1185	} else {
1186		dio->opf = REQ_OP_READ;
1187	}
1188
1189	/*
1190	 * For AIO O_(D)SYNC writes we need to defer completions to a workqueue
1191	 * so that we can call ->fsync.
1192	 */
1193	if (dio->is_async && iov_iter_rw(iter) == WRITE) {
1194		retval = 0;
1195		if (iocb_is_dsync(iocb))
1196			retval = dio_set_defer_completion(dio);
1197		else if (!dio->inode->i_sb->s_dio_done_wq) {
1198			/*
1199			 * In case of AIO write racing with buffered read we
1200			 * need to defer completion. We can't decide this now,
1201			 * however the workqueue needs to be initialized here.
1202			 */
1203			retval = sb_init_dio_done_wq(dio->inode->i_sb);
1204		}
1205		if (retval)
1206			goto fail_dio;
1207	}
1208
1209	/*
1210	 * Will be decremented at I/O completion time.
1211	 */
1212	inode_dio_begin(inode);
1213
1214	sdio.blkbits = blkbits;
1215	sdio.blkfactor = i_blkbits - blkbits;
1216	sdio.block_in_file = offset >> blkbits;
1217
1218	sdio.get_block = get_block;
1219	dio->end_io = end_io;
1220	sdio.final_block_in_bio = -1;
1221	sdio.next_block_for_io = -1;
1222
1223	dio->iocb = iocb;
1224
1225	spin_lock_init(&dio->bio_lock);
1226	dio->refcount = 1;
1227
1228	dio->should_dirty = user_backed_iter(iter) && iov_iter_rw(iter) == READ;
1229	sdio.iter = iter;
1230	sdio.final_block_in_request = end >> blkbits;
1231
1232	/*
1233	 * In case of non-aligned buffers, we may need 2 more
1234	 * pages since we need to zero out first and last block.
1235	 */
1236	if (unlikely(sdio.blkfactor))
1237		sdio.pages_in_io = 2;
1238
1239	sdio.pages_in_io += iov_iter_npages(iter, INT_MAX);
1240
1241	blk_start_plug(&plug);
1242
1243	retval = do_direct_IO(dio, &sdio, &map_bh);
1244	if (retval)
1245		dio_cleanup(dio, &sdio);
1246
1247	if (retval == -ENOTBLK) {
1248		/*
1249		 * The remaining part of the request will be
1250		 * handled by buffered I/O when we return
1251		 */
1252		retval = 0;
1253	}
1254	/*
1255	 * There may be some unwritten disk at the end of a part-written
1256	 * fs-block-sized block.  Go zero that now.
1257	 */
1258	dio_zero_block(dio, &sdio, 1, &map_bh);
1259
1260	if (sdio.cur_page) {
1261		ssize_t ret2;
1262
1263		ret2 = dio_send_cur_page(dio, &sdio, &map_bh);
1264		if (retval == 0)
1265			retval = ret2;
1266		dio_unpin_page(dio, sdio.cur_page);
1267		sdio.cur_page = NULL;
1268	}
1269	if (sdio.bio)
1270		dio_bio_submit(dio, &sdio);
1271
1272	blk_finish_plug(&plug);
1273
1274	/*
1275	 * It is possible that, we return short IO due to end of file.
1276	 * In that case, we need to release all the pages we got hold on.
1277	 */
1278	dio_cleanup(dio, &sdio);
1279
1280	/*
1281	 * All block lookups have been performed. For READ requests
1282	 * we can let i_rwsem go now that its achieved its purpose
1283	 * of protecting us from looking up uninitialized blocks.
1284	 */
1285	if (iov_iter_rw(iter) == READ && (dio->flags & DIO_LOCKING))
1286		inode_unlock(dio->inode);
1287
1288	/*
1289	 * The only time we want to leave bios in flight is when a successful
1290	 * partial aio read or full aio write have been setup.  In that case
1291	 * bio completion will call aio_complete.  The only time it's safe to
1292	 * call aio_complete is when we return -EIOCBQUEUED, so we key on that.
1293	 * This had *better* be the only place that raises -EIOCBQUEUED.
1294	 */
1295	BUG_ON(retval == -EIOCBQUEUED);
1296	if (dio->is_async && retval == 0 && dio->result &&
1297	    (iov_iter_rw(iter) == READ || dio->result == count))
1298		retval = -EIOCBQUEUED;
1299	else
1300		dio_await_completion(dio);
1301
1302	if (drop_refcount(dio) == 0) {
1303		retval = dio_complete(dio, retval, DIO_COMPLETE_INVALIDATE);
1304	} else
1305		BUG_ON(retval != -EIOCBQUEUED);
1306
1307	return retval;
1308
1309fail_dio:
1310	if (dio->flags & DIO_LOCKING && iov_iter_rw(iter) == READ)
1311		inode_unlock(inode);
1312
1313	kmem_cache_free(dio_cache, dio);
1314	return retval;
1315}
1316EXPORT_SYMBOL(__blockdev_direct_IO);
1317
1318static __init int dio_init(void)
1319{
1320	dio_cache = KMEM_CACHE(dio, SLAB_PANIC);
1321	return 0;
1322}
1323module_init(dio_init)