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    /*
     * fs/dax.c - Direct Access filesystem code
     * Copyright (c) 2013-2014 Intel Corporation
     * Author: Matthew Wilcox <matthew.r.wilcox@intel.com>
     * Author: Ross Zwisler <ross.zwisler@linux.intel.com>
     *
     * This program is free software; you can redistribute it and/or modify it
     * under the terms and conditions of the GNU General Public License,
     * version 2, as published by the Free Software Foundation.
     *
     * This program is distributed in the hope it will be useful, but WITHOUT
     * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
     * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
     * more details.
     */
    
    #include <linux/atomic.h>
    #include <linux/blkdev.h>
    #include <linux/buffer_head.h>
    #include <linux/dax.h>
    #include <linux/fs.h>
    #include <linux/genhd.h>
    #include <linux/highmem.h>
    #include <linux/memcontrol.h>
    #include <linux/mm.h>
    #include <linux/mutex.h>
    #include <linux/pagevec.h>
    #include <linux/pmem.h>
    #include <linux/sched.h>
    #include <linux/uio.h>
    #include <linux/vmstat.h>
    #include <linux/pfn_t.h>
    #include <linux/sizes.h>
    #include <linux/iomap.h>
    #include "internal.h"
    
    /*
     * We use lowest available bit in exceptional entry for locking, other two
     * bits to determine entry type. In total 3 special bits.
     */
    #define RADIX_DAX_SHIFT	(RADIX_TREE_EXCEPTIONAL_SHIFT + 3)
    #define RADIX_DAX_PTE (1 << (RADIX_TREE_EXCEPTIONAL_SHIFT + 1))
    #define RADIX_DAX_PMD (1 << (RADIX_TREE_EXCEPTIONAL_SHIFT + 2))
    #define RADIX_DAX_TYPE_MASK (RADIX_DAX_PTE | RADIX_DAX_PMD)
    #define RADIX_DAX_TYPE(entry) ((unsigned long)entry & RADIX_DAX_TYPE_MASK)
    #define RADIX_DAX_SECTOR(entry) (((unsigned long)entry >> RADIX_DAX_SHIFT))
    #define RADIX_DAX_ENTRY(sector, pmd) ((void *)((unsigned long)sector << \
    		RADIX_DAX_SHIFT | (pmd ? RADIX_DAX_PMD : RADIX_DAX_PTE) | \
    		RADIX_TREE_EXCEPTIONAL_ENTRY))
    
    /* We choose 4096 entries - same as per-zone page wait tables */
    #define DAX_WAIT_TABLE_BITS 12
    #define DAX_WAIT_TABLE_ENTRIES (1 << DAX_WAIT_TABLE_BITS)
    
    wait_queue_head_t wait_table[DAX_WAIT_TABLE_ENTRIES];
    
    static int __init init_dax_wait_table(void)
    {
    	int i;
    
    	for (i = 0; i < DAX_WAIT_TABLE_ENTRIES; i++)
    		init_waitqueue_head(wait_table + i);
    	return 0;
    }
    fs_initcall(init_dax_wait_table);
    
    static wait_queue_head_t *dax_entry_waitqueue(struct address_space *mapping,
    					      pgoff_t index)
    {
    	unsigned long hash = hash_long((unsigned long)mapping ^ index,
    				       DAX_WAIT_TABLE_BITS);
    	return wait_table + hash;
    }
    
    static long dax_map_atomic(struct block_device *bdev, struct blk_dax_ctl *dax)
    {
    	struct request_queue *q = bdev->bd_queue;
    	long rc = -EIO;
    
    	dax->addr = ERR_PTR(-EIO);
    	if (blk_queue_enter(q, true) != 0)
    		return rc;
    
    	rc = bdev_direct_access(bdev, dax);
    	if (rc < 0) {
    		dax->addr = ERR_PTR(rc);
    		blk_queue_exit(q);
    		return rc;
    	}
    	return rc;
    }
    
    static void dax_unmap_atomic(struct block_device *bdev,
    		const struct blk_dax_ctl *dax)
    {
    	if (IS_ERR(dax->addr))
    		return;
    	blk_queue_exit(bdev->bd_queue);
    }
    
    struct page *read_dax_sector(struct block_device *bdev, sector_t n)
    {
    	struct page *page = alloc_pages(GFP_KERNEL, 0);
    	struct blk_dax_ctl dax = {
    		.size = PAGE_SIZE,
    		.sector = n & ~((((int) PAGE_SIZE) / 512) - 1),
    	};
    	long rc;
    
    	if (!page)
    		return ERR_PTR(-ENOMEM);
    
    	rc = dax_map_atomic(bdev, &dax);
    	if (rc < 0)
    		return ERR_PTR(rc);
    	memcpy_from_pmem(page_address(page), dax.addr, PAGE_SIZE);
    	dax_unmap_atomic(bdev, &dax);
    	return page;
    }
    
    static bool buffer_written(struct buffer_head *bh)
    {
    	return buffer_mapped(bh) && !buffer_unwritten(bh);
    }
    
    /*
     * When ext4 encounters a hole, it returns without modifying the buffer_head
     * which means that we can't trust b_size.  To cope with this, we set b_state
     * to 0 before calling get_block and, if any bit is set, we know we can trust
     * b_size.  Unfortunate, really, since ext4 knows precisely how long a hole is
     * and would save us time calling get_block repeatedly.
     */
    static bool buffer_size_valid(struct buffer_head *bh)
    {
    	return bh->b_state != 0;
    }
    
    
    static sector_t to_sector(const struct buffer_head *bh,
    		const struct inode *inode)
    {
    	sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);
    
    	return sector;
    }
    
    static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
    		      loff_t start, loff_t end, get_block_t get_block,
    		      struct buffer_head *bh)
    {
    	loff_t pos = start, max = start, bh_max = start;
    	bool hole = false;
    	struct block_device *bdev = NULL;
    	int rw = iov_iter_rw(iter), rc;
    	long map_len = 0;
    	struct blk_dax_ctl dax = {
    		.addr = ERR_PTR(-EIO),
    	};
    	unsigned blkbits = inode->i_blkbits;
    	sector_t file_blks = (i_size_read(inode) + (1 << blkbits) - 1)
    								>> blkbits;
    
    	if (rw == READ)
    		end = min(end, i_size_read(inode));
    
    	while (pos < end) {
    		size_t len;
    		if (pos == max) {
    			long page = pos >> PAGE_SHIFT;
    			sector_t block = page << (PAGE_SHIFT - blkbits);
    			unsigned first = pos - (block << blkbits);
    			long size;
    
    			if (pos == bh_max) {
    				bh->b_size = PAGE_ALIGN(end - pos);
    				bh->b_state = 0;
    				rc = get_block(inode, block, bh, rw == WRITE);
    				if (rc)
    					break;
    				if (!buffer_size_valid(bh))
    					bh->b_size = 1 << blkbits;
    				bh_max = pos - first + bh->b_size;
    				bdev = bh->b_bdev;
    				/*
    				 * We allow uninitialized buffers for writes
    				 * beyond EOF as those cannot race with faults
    				 */
    				WARN_ON_ONCE(
    					(buffer_new(bh) && block < file_blks) ||
    					(rw == WRITE && buffer_unwritten(bh)));
    			} else {
    				unsigned done = bh->b_size -
    						(bh_max - (pos - first));
    				bh->b_blocknr += done >> blkbits;
    				bh->b_size -= done;
    			}
    
    			hole = rw == READ && !buffer_written(bh);
    			if (hole) {
    				size = bh->b_size - first;
    			} else {
    				dax_unmap_atomic(bdev, &dax);
    				dax.sector = to_sector(bh, inode);
    				dax.size = bh->b_size;
    				map_len = dax_map_atomic(bdev, &dax);
    				if (map_len < 0) {
    					rc = map_len;
    					break;
    				}
    				dax.addr += first;
    				size = map_len - first;
    			}
    			/*
    			 * pos + size is one past the last offset for IO,
    			 * so pos + size can overflow loff_t at extreme offsets.
    			 * Cast to u64 to catch this and get the true minimum.
    			 */
    			max = min_t(u64, pos + size, end);
    		}
    
    		if (iov_iter_rw(iter) == WRITE) {
    			len = copy_from_iter_pmem(dax.addr, max - pos, iter);
    		} else if (!hole)
    			len = copy_to_iter((void __force *) dax.addr, max - pos,
    					iter);
    		else
    			len = iov_iter_zero(max - pos, iter);
    
    		if (!len) {
    			rc = -EFAULT;
    			break;
    		}
    
    		pos += len;
    		if (!IS_ERR(dax.addr))
    			dax.addr += len;
    	}
    
    	dax_unmap_atomic(bdev, &dax);
    
    	return (pos == start) ? rc : pos - start;
    }
    
    /**
     * dax_do_io - Perform I/O to a DAX file
     * @iocb: The control block for this I/O
     * @inode: The file which the I/O is directed at
     * @iter: The addresses to do I/O from or to
     * @get_block: The filesystem method used to translate file offsets to blocks
     * @end_io: A filesystem callback for I/O completion
     * @flags: See below
     *
     * This function uses the same locking scheme as do_blockdev_direct_IO:
     * If @flags has DIO_LOCKING set, we assume that the i_mutex is held by the
     * caller for writes.  For reads, we take and release the i_mutex ourselves.
     * If DIO_LOCKING is not set, the filesystem takes care of its own locking.
     * As with do_blockdev_direct_IO(), we increment i_dio_count while the I/O
     * is in progress.
     */
    ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
    		  struct iov_iter *iter, get_block_t get_block,
    		  dio_iodone_t end_io, int flags)
    {
    	struct buffer_head bh;
    	ssize_t retval = -EINVAL;
    	loff_t pos = iocb->ki_pos;
    	loff_t end = pos + iov_iter_count(iter);
    
    	memset(&bh, 0, sizeof(bh));
    	bh.b_bdev = inode->i_sb->s_bdev;
    
    	if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
    		inode_lock(inode);
    
    	/* Protects against truncate */
    	if (!(flags & DIO_SKIP_DIO_COUNT))
    		inode_dio_begin(inode);
    
    	retval = dax_io(inode, iter, pos, end, get_block, &bh);
    
    	if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
    		inode_unlock(inode);
    
    	if (end_io) {
    		int err;
    
    		err = end_io(iocb, pos, retval, bh.b_private);
    		if (err)
    			retval = err;
    	}
    
    	if (!(flags & DIO_SKIP_DIO_COUNT))
    		inode_dio_end(inode);
    	return retval;
    }
    EXPORT_SYMBOL_GPL(dax_do_io);
    
    /*
     * DAX radix tree locking
     */
    struct exceptional_entry_key {
    	struct address_space *mapping;
    	unsigned long index;
    };
    
    struct wait_exceptional_entry_queue {
    	wait_queue_t wait;
    	struct exceptional_entry_key key;
    };
    
    static int wake_exceptional_entry_func(wait_queue_t *wait, unsigned int mode,
    				       int sync, void *keyp)
    {
    	struct exceptional_entry_key *key = keyp;
    	struct wait_exceptional_entry_queue *ewait =
    		container_of(wait, struct wait_exceptional_entry_queue, wait);
    
    	if (key->mapping != ewait->key.mapping ||
    	    key->index != ewait->key.index)
    		return 0;
    	return autoremove_wake_function(wait, mode, sync, NULL);
    }
    
    /*
     * Check whether the given slot is locked. The function must be called with
     * mapping->tree_lock held
     */
    static inline int slot_locked(struct address_space *mapping, void **slot)
    {
    	unsigned long entry = (unsigned long)
    		radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
    	return entry & RADIX_DAX_ENTRY_LOCK;
    }
    
    /*
     * Mark the given slot is locked. The function must be called with
     * mapping->tree_lock held
     */
    static inline void *lock_slot(struct address_space *mapping, void **slot)
    {
    	unsigned long entry = (unsigned long)
    		radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
    
    	entry |= RADIX_DAX_ENTRY_LOCK;
    	radix_tree_replace_slot(slot, (void *)entry);
    	return (void *)entry;
    }
    
    /*
     * Mark the given slot is unlocked. The function must be called with
     * mapping->tree_lock held
     */
    static inline void *unlock_slot(struct address_space *mapping, void **slot)
    {
    	unsigned long entry = (unsigned long)
    		radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
    
    	entry &= ~(unsigned long)RADIX_DAX_ENTRY_LOCK;
    	radix_tree_replace_slot(slot, (void *)entry);
    	return (void *)entry;
    }
    
    /*
     * Lookup entry in radix tree, wait for it to become unlocked if it is
     * exceptional entry and return it. The caller must call
     * put_unlocked_mapping_entry() when he decided not to lock the entry or
     * put_locked_mapping_entry() when he locked the entry and now wants to
     * unlock it.
     *
     * The function must be called with mapping->tree_lock held.
     */
    static void *get_unlocked_mapping_entry(struct address_space *mapping,
    					pgoff_t index, void ***slotp)
    {
    	void *ret, **slot;
    	struct wait_exceptional_entry_queue ewait;
    	wait_queue_head_t *wq = dax_entry_waitqueue(mapping, index);
    
    	init_wait(&ewait.wait);
    	ewait.wait.func = wake_exceptional_entry_func;
    	ewait.key.mapping = mapping;
    	ewait.key.index = index;
    
    	for (;;) {
    		ret = __radix_tree_lookup(&mapping->page_tree, index, NULL,
    					  &slot);
    		if (!ret || !radix_tree_exceptional_entry(ret) ||
    		    !slot_locked(mapping, slot)) {
    			if (slotp)
    				*slotp = slot;
    			return ret;
    		}
    		prepare_to_wait_exclusive(wq, &ewait.wait,
    					  TASK_UNINTERRUPTIBLE);
    		spin_unlock_irq(&mapping->tree_lock);
    		schedule();
    		finish_wait(wq, &ewait.wait);
    		spin_lock_irq(&mapping->tree_lock);
    	}
    }
    
    /*
     * Find radix tree entry at given index. If it points to a page, return with
     * the page locked. If it points to the exceptional entry, return with the
     * radix tree entry locked. If the radix tree doesn't contain given index,
     * create empty exceptional entry for the index and return with it locked.
     *
     * Note: Unlike filemap_fault() we don't honor FAULT_FLAG_RETRY flags. For
     * persistent memory the benefit is doubtful. We can add that later if we can
     * show it helps.
     */
    static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index)
    {
    	void *ret, **slot;
    
    restart:
    	spin_lock_irq(&mapping->tree_lock);
    	ret = get_unlocked_mapping_entry(mapping, index, &slot);
    	/* No entry for given index? Make sure radix tree is big enough. */
    	if (!ret) {
    		int err;
    
    		spin_unlock_irq(&mapping->tree_lock);
    		err = radix_tree_preload(
    				mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM);
    		if (err)
    			return ERR_PTR(err);
    		ret = (void *)(RADIX_TREE_EXCEPTIONAL_ENTRY |
    			       RADIX_DAX_ENTRY_LOCK);
    		spin_lock_irq(&mapping->tree_lock);
    		err = radix_tree_insert(&mapping->page_tree, index, ret);
    		radix_tree_preload_end();
    		if (err) {
    			spin_unlock_irq(&mapping->tree_lock);
    			/* Someone already created the entry? */
    			if (err == -EEXIST)
    				goto restart;
    			return ERR_PTR(err);
    		}
    		/* Good, we have inserted empty locked entry into the tree. */
    		mapping->nrexceptional++;
    		spin_unlock_irq(&mapping->tree_lock);
    		return ret;
    	}
    	/* Normal page in radix tree? */
    	if (!radix_tree_exceptional_entry(ret)) {
    		struct page *page = ret;
    
    		get_page(page);
    		spin_unlock_irq(&mapping->tree_lock);
    		lock_page(page);
    		/* Page got truncated? Retry... */
    		if (unlikely(page->mapping != mapping)) {
    			unlock_page(page);
    			put_page(page);
    			goto restart;
    		}
    		return page;
    	}
    	ret = lock_slot(mapping, slot);
    	spin_unlock_irq(&mapping->tree_lock);
    	return ret;
    }
    
    void dax_wake_mapping_entry_waiter(struct address_space *mapping,
    				   pgoff_t index, bool wake_all)
    {
    	wait_queue_head_t *wq = dax_entry_waitqueue(mapping, index);
    
    	/*
    	 * Checking for locked entry and prepare_to_wait_exclusive() happens
    	 * under mapping->tree_lock, ditto for entry handling in our callers.
    	 * So at this point all tasks that could have seen our entry locked
    	 * must be in the waitqueue and the following check will see them.
    	 */
    	if (waitqueue_active(wq)) {
    		struct exceptional_entry_key key;
    
    		key.mapping = mapping;
    		key.index = index;
    		__wake_up(wq, TASK_NORMAL, wake_all ? 0 : 1, &key);
    	}
    }
    
    void dax_unlock_mapping_entry(struct address_space *mapping, pgoff_t index)
    {
    	void *ret, **slot;
    
    	spin_lock_irq(&mapping->tree_lock);
    	ret = __radix_tree_lookup(&mapping->page_tree, index, NULL, &slot);
    	if (WARN_ON_ONCE(!ret || !radix_tree_exceptional_entry(ret) ||
    			 !slot_locked(mapping, slot))) {
    		spin_unlock_irq(&mapping->tree_lock);
    		return;
    	}
    	unlock_slot(mapping, slot);
    	spin_unlock_irq(&mapping->tree_lock);
    	dax_wake_mapping_entry_waiter(mapping, index, false);
    }
    
    static void put_locked_mapping_entry(struct address_space *mapping,
    				     pgoff_t index, void *entry)
    {
    	if (!radix_tree_exceptional_entry(entry)) {
    		unlock_page(entry);
    		put_page(entry);
    	} else {
    		dax_unlock_mapping_entry(mapping, index);
    	}
    }
    
    /*
     * Called when we are done with radix tree entry we looked up via
     * get_unlocked_mapping_entry() and which we didn't lock in the end.
     */
    static void put_unlocked_mapping_entry(struct address_space *mapping,
    				       pgoff_t index, void *entry)
    {
    	if (!radix_tree_exceptional_entry(entry))
    		return;
    
    	/* We have to wake up next waiter for the radix tree entry lock */
    	dax_wake_mapping_entry_waiter(mapping, index, false);
    }
    
    /*
     * Delete exceptional DAX entry at @index from @mapping. Wait for radix tree
     * entry to get unlocked before deleting it.
     */
    int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index)
    {
    	void *entry;
    
    	spin_lock_irq(&mapping->tree_lock);
    	entry = get_unlocked_mapping_entry(mapping, index, NULL);
    	/*
    	 * This gets called from truncate / punch_hole path. As such, the caller
    	 * must hold locks protecting against concurrent modifications of the
    	 * radix tree (usually fs-private i_mmap_sem for writing). Since the
    	 * caller has seen exceptional entry for this index, we better find it
    	 * at that index as well...
    	 */
    	if (WARN_ON_ONCE(!entry || !radix_tree_exceptional_entry(entry))) {
    		spin_unlock_irq(&mapping->tree_lock);
    		return 0;
    	}
    	radix_tree_delete(&mapping->page_tree, index);
    	mapping->nrexceptional--;
    	spin_unlock_irq(&mapping->tree_lock);
    	dax_wake_mapping_entry_waiter(mapping, index, true);
    
    	return 1;
    }
    
    /*
     * The user has performed a load from a hole in the file.  Allocating
     * a new page in the file would cause excessive storage usage for
     * workloads with sparse files.  We allocate a page cache page instead.
     * We'll kick it out of the page cache if it's ever written to,
     * otherwise it will simply fall out of the page cache under memory
     * pressure without ever having been dirtied.
     */
    static int dax_load_hole(struct address_space *mapping, void *entry,
    			 struct vm_fault *vmf)
    {
    	struct page *page;
    
    	/* Hole page already exists? Return it...  */
    	if (!radix_tree_exceptional_entry(entry)) {
    		vmf->page = entry;
    		return VM_FAULT_LOCKED;
    	}
    
    	/* This will replace locked radix tree entry with a hole page */
    	page = find_or_create_page(mapping, vmf->pgoff,
    				   vmf->gfp_mask | __GFP_ZERO);
    	if (!page) {
    		put_locked_mapping_entry(mapping, vmf->pgoff, entry);
    		return VM_FAULT_OOM;
    	}
    	vmf->page = page;
    	return VM_FAULT_LOCKED;
    }
    
    static int copy_user_dax(struct block_device *bdev, sector_t sector, size_t size,
    		struct page *to, unsigned long vaddr)
    {
    	struct blk_dax_ctl dax = {
    		.sector = sector,
    		.size = size,
    	};
    	void *vto;
    
    	if (dax_map_atomic(bdev, &dax) < 0)
    		return PTR_ERR(dax.addr);
    	vto = kmap_atomic(to);
    	copy_user_page(vto, (void __force *)dax.addr, vaddr, to);
    	kunmap_atomic(vto);
    	dax_unmap_atomic(bdev, &dax);
    	return 0;
    }
    
    #define DAX_PMD_INDEX(page_index) (page_index & (PMD_MASK >> PAGE_SHIFT))
    
    static void *dax_insert_mapping_entry(struct address_space *mapping,
    				      struct vm_fault *vmf,
    				      void *entry, sector_t sector)
    {
    	struct radix_tree_root *page_tree = &mapping->page_tree;
    	int error = 0;
    	bool hole_fill = false;
    	void *new_entry;
    	pgoff_t index = vmf->pgoff;
    
    	if (vmf->flags & FAULT_FLAG_WRITE)
    		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
    
    	/* Replacing hole page with block mapping? */
    	if (!radix_tree_exceptional_entry(entry)) {
    		hole_fill = true;
    		/*
    		 * Unmap the page now before we remove it from page cache below.
    		 * The page is locked so it cannot be faulted in again.
    		 */
    		unmap_mapping_range(mapping, vmf->pgoff << PAGE_SHIFT,
    				    PAGE_SIZE, 0);
    		error = radix_tree_preload(vmf->gfp_mask & ~__GFP_HIGHMEM);
    		if (error)
    			return ERR_PTR(error);
    	}
    
    	spin_lock_irq(&mapping->tree_lock);
    	new_entry = (void *)((unsigned long)RADIX_DAX_ENTRY(sector, false) |
    		       RADIX_DAX_ENTRY_LOCK);
    	if (hole_fill) {
    		__delete_from_page_cache(entry, NULL);
    		/* Drop pagecache reference */
    		put_page(entry);
    		error = radix_tree_insert(page_tree, index, new_entry);
    		if (error) {
    			new_entry = ERR_PTR(error);
    			goto unlock;
    		}
    		mapping->nrexceptional++;
    	} else {
    		void **slot;
    		void *ret;
    
    		ret = __radix_tree_lookup(page_tree, index, NULL, &slot);
    		WARN_ON_ONCE(ret != entry);
    		radix_tree_replace_slot(slot, new_entry);
    	}
    	if (vmf->flags & FAULT_FLAG_WRITE)
    		radix_tree_tag_set(page_tree, index, PAGECACHE_TAG_DIRTY);
     unlock:
    	spin_unlock_irq(&mapping->tree_lock);
    	if (hole_fill) {
    		radix_tree_preload_end();
    		/*
    		 * We don't need hole page anymore, it has been replaced with
    		 * locked radix tree entry now.
    		 */
    		if (mapping->a_ops->freepage)
    			mapping->a_ops->freepage(entry);
    		unlock_page(entry);
    		put_page(entry);
    	}
    	return new_entry;
    }
    
    static int dax_writeback_one(struct block_device *bdev,
    		struct address_space *mapping, pgoff_t index, void *entry)
    {
    	struct radix_tree_root *page_tree = &mapping->page_tree;
    	int type = RADIX_DAX_TYPE(entry);
    	struct radix_tree_node *node;
    	struct blk_dax_ctl dax;
    	void **slot;
    	int ret = 0;
    
    	spin_lock_irq(&mapping->tree_lock);
    	/*
    	 * Regular page slots are stabilized by the page lock even
    	 * without the tree itself locked.  These unlocked entries
    	 * need verification under the tree lock.
    	 */
    	if (!__radix_tree_lookup(page_tree, index, &node, &slot))
    		goto unlock;
    	if (*slot != entry)
    		goto unlock;
    
    	/* another fsync thread may have already written back this entry */
    	if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
    		goto unlock;
    
    	if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD)) {
    		ret = -EIO;
    		goto unlock;
    	}
    
    	dax.sector = RADIX_DAX_SECTOR(entry);
    	dax.size = (type == RADIX_DAX_PMD ? PMD_SIZE : PAGE_SIZE);
    	spin_unlock_irq(&mapping->tree_lock);
    
    	/*
    	 * We cannot hold tree_lock while calling dax_map_atomic() because it
    	 * eventually calls cond_resched().
    	 */
    	ret = dax_map_atomic(bdev, &dax);
    	if (ret < 0)
    		return ret;
    
    	if (WARN_ON_ONCE(ret < dax.size)) {
    		ret = -EIO;
    		goto unmap;
    	}
    
    	wb_cache_pmem(dax.addr, dax.size);
    
    	spin_lock_irq(&mapping->tree_lock);
    	radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
    	spin_unlock_irq(&mapping->tree_lock);
     unmap:
    	dax_unmap_atomic(bdev, &dax);
    	return ret;
    
     unlock:
    	spin_unlock_irq(&mapping->tree_lock);
    	return ret;
    }
    
    /*
     * Flush the mapping to the persistent domain within the byte range of [start,
     * end]. This is required by data integrity operations to ensure file data is
     * on persistent storage prior to completion of the operation.
     */
    int dax_writeback_mapping_range(struct address_space *mapping,
    		struct block_device *bdev, struct writeback_control *wbc)
    {
    	struct inode *inode = mapping->host;
    	pgoff_t start_index, end_index, pmd_index;
    	pgoff_t indices[PAGEVEC_SIZE];
    	struct pagevec pvec;
    	bool done = false;
    	int i, ret = 0;
    	void *entry;
    
    	if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT))
    		return -EIO;
    
    	if (!mapping->nrexceptional || wbc->sync_mode != WB_SYNC_ALL)
    		return 0;
    
    	start_index = wbc->range_start >> PAGE_SHIFT;
    	end_index = wbc->range_end >> PAGE_SHIFT;
    	pmd_index = DAX_PMD_INDEX(start_index);
    
    	rcu_read_lock();
    	entry = radix_tree_lookup(&mapping->page_tree, pmd_index);
    	rcu_read_unlock();
    
    	/* see if the start of our range is covered by a PMD entry */
    	if (entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
    		start_index = pmd_index;
    
    	tag_pages_for_writeback(mapping, start_index, end_index);
    
    	pagevec_init(&pvec, 0);
    	while (!done) {
    		pvec.nr = find_get_entries_tag(mapping, start_index,
    				PAGECACHE_TAG_TOWRITE, PAGEVEC_SIZE,
    				pvec.pages, indices);
    
    		if (pvec.nr == 0)
    			break;
    
    		for (i = 0; i < pvec.nr; i++) {
    			if (indices[i] > end_index) {
    				done = true;
    				break;
    			}
    
    			ret = dax_writeback_one(bdev, mapping, indices[i],
    					pvec.pages[i]);
    			if (ret < 0)
    				return ret;
    		}
    	}
    	return 0;
    }
    EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
    
    static int dax_insert_mapping(struct address_space *mapping,
    		struct block_device *bdev, sector_t sector, size_t size,
    		void **entryp, struct vm_area_struct *vma, struct vm_fault *vmf)
    {
    	unsigned long vaddr = (unsigned long)vmf->virtual_address;
    	struct blk_dax_ctl dax = {
    		.sector = sector,
    		.size = size,
    	};
    	void *ret;
    	void *entry = *entryp;
    
    	if (dax_map_atomic(bdev, &dax) < 0)
    		return PTR_ERR(dax.addr);
    	dax_unmap_atomic(bdev, &dax);
    
    	ret = dax_insert_mapping_entry(mapping, vmf, entry, dax.sector);
    	if (IS_ERR(ret))
    		return PTR_ERR(ret);
    	*entryp = ret;
    
    	return vm_insert_mixed(vma, vaddr, dax.pfn);
    }
    
    /**
     * dax_fault - handle a page fault on a DAX file
     * @vma: The virtual memory area where the fault occurred
     * @vmf: The description of the fault
     * @get_block: The filesystem method used to translate file offsets to blocks
     *
     * When a page fault occurs, filesystems may call this helper in their
     * fault handler for DAX files. dax_fault() assumes the caller has done all
     * the necessary locking for the page fault to proceed successfully.
     */
    int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
    			get_block_t get_block)
    {
    	struct file *file = vma->vm_file;
    	struct address_space *mapping = file->f_mapping;
    	struct inode *inode = mapping->host;
    	void *entry;
    	struct buffer_head bh;
    	unsigned long vaddr = (unsigned long)vmf->virtual_address;
    	unsigned blkbits = inode->i_blkbits;
    	sector_t block;
    	pgoff_t size;
    	int error;
    	int major = 0;
    
    	/*
    	 * Check whether offset isn't beyond end of file now. Caller is supposed
    	 * to hold locks serializing us with truncate / punch hole so this is
    	 * a reliable test.
    	 */
    	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
    	if (vmf->pgoff >= size)
    		return VM_FAULT_SIGBUS;
    
    	memset(&bh, 0, sizeof(bh));
    	block = (sector_t)vmf->pgoff << (PAGE_SHIFT - blkbits);
    	bh.b_bdev = inode->i_sb->s_bdev;
    	bh.b_size = PAGE_SIZE;
    
    	entry = grab_mapping_entry(mapping, vmf->pgoff);
    	if (IS_ERR(entry)) {
    		error = PTR_ERR(entry);
    		goto out;
    	}
    
    	error = get_block(inode, block, &bh, 0);
    	if (!error && (bh.b_size < PAGE_SIZE))
    		error = -EIO;		/* fs corruption? */
    	if (error)
    		goto unlock_entry;
    
    	if (vmf->cow_page) {
    		struct page *new_page = vmf->cow_page;
    		if (buffer_written(&bh))
    			error = copy_user_dax(bh.b_bdev, to_sector(&bh, inode),
    					bh.b_size, new_page, vaddr);
    		else
    			clear_user_highpage(new_page, vaddr);
    		if (error)
    			goto unlock_entry;
    		if (!radix_tree_exceptional_entry(entry)) {
    			vmf->page = entry;
    			return VM_FAULT_LOCKED;
    		}
    		vmf->entry = entry;
    		return VM_FAULT_DAX_LOCKED;
    	}
    
    	if (!buffer_mapped(&bh)) {
    		if (vmf->flags & FAULT_FLAG_WRITE) {
    			error = get_block(inode, block, &bh, 1);
    			count_vm_event(PGMAJFAULT);
    			mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
    			major = VM_FAULT_MAJOR;
    			if (!error && (bh.b_size < PAGE_SIZE))
    				error = -EIO;
    			if (error)
    				goto unlock_entry;
    		} else {
    			return dax_load_hole(mapping, entry, vmf);
    		}
    	}
    
    	/* Filesystem should not return unwritten buffers to us! */
    	WARN_ON_ONCE(buffer_unwritten(&bh) || buffer_new(&bh));
    	error = dax_insert_mapping(mapping, bh.b_bdev, to_sector(&bh, inode),
    			bh.b_size, &entry, vma, vmf);
     unlock_entry:
    	put_locked_mapping_entry(mapping, vmf->pgoff, entry);
     out:
    	if (error == -ENOMEM)
    		return VM_FAULT_OOM | major;
    	/* -EBUSY is fine, somebody else faulted on the same PTE */
    	if ((error < 0) && (error != -EBUSY))
    		return VM_FAULT_SIGBUS | major;
    	return VM_FAULT_NOPAGE | major;
    }
    EXPORT_SYMBOL_GPL(dax_fault);
    
    #if defined(CONFIG_TRANSPARENT_HUGEPAGE)
    /*
     * The 'colour' (ie low bits) within a PMD of a page offset.  This comes up
     * more often than one might expect in the below function.
     */
    #define PG_PMD_COLOUR	((PMD_SIZE >> PAGE_SHIFT) - 1)
    
    static void __dax_dbg(struct buffer_head *bh, unsigned long address,
    		const char *reason, const char *fn)
    {
    	if (bh) {
    		char bname[BDEVNAME_SIZE];
    		bdevname(bh->b_bdev, bname);
    		pr_debug("%s: %s addr: %lx dev %s state %lx start %lld "
    			"length %zd fallback: %s\n", fn, current->comm,
    			address, bname, bh->b_state, (u64)bh->b_blocknr,
    			bh->b_size, reason);
    	} else {
    		pr_debug("%s: %s addr: %lx fallback: %s\n", fn,
    			current->comm, address, reason);
    	}
    }
    
    #define dax_pmd_dbg(bh, address, reason)	__dax_dbg(bh, address, reason, "dax_pmd")
    
    /**
     * dax_pmd_fault - handle a PMD fault on a DAX file
     * @vma: The virtual memory area where the fault occurred
     * @vmf: The description of the fault
     * @get_block: The filesystem method used to translate file offsets to blocks
     *
     * When a page fault occurs, filesystems may call this helper in their
     * pmd_fault handler for DAX files.
     */
    int dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
    		pmd_t *pmd, unsigned int flags, get_block_t get_block)
    {
    	struct file *file = vma->vm_file;
    	struct address_space *mapping = file->f_mapping;
    	struct inode *inode = mapping->host;
    	struct buffer_head bh;
    	unsigned blkbits = inode->i_blkbits;
    	unsigned long pmd_addr = address & PMD_MASK;
    	bool write = flags & FAULT_FLAG_WRITE;
    	struct block_device *bdev;
    	pgoff_t size, pgoff;
    	sector_t block;
    	int result = 0;
    	bool alloc = false;
    
    	/* dax pmd mappings require pfn_t_devmap() */
    	if (!IS_ENABLED(CONFIG_FS_DAX_PMD))
    		return VM_FAULT_FALLBACK;
    
    	/* Fall back to PTEs if we're going to COW */
    	if (write && !(vma->vm_flags & VM_SHARED)) {
    		split_huge_pmd(vma, pmd, address);
    		dax_pmd_dbg(NULL, address, "cow write");
    		return VM_FAULT_FALLBACK;
    	}
    	/* If the PMD would extend outside the VMA */
    	if (pmd_addr < vma->vm_start) {
    		dax_pmd_dbg(NULL, address, "vma start unaligned");
    		return VM_FAULT_FALLBACK;
    	}
    	if ((pmd_addr + PMD_SIZE) > vma->vm_end) {
    		dax_pmd_dbg(NULL, address, "vma end unaligned");
    		return VM_FAULT_FALLBACK;
    	}
    
    	pgoff = linear_page_index(vma, pmd_addr);
    	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
    	if (pgoff >= size)
    		return VM_FAULT_SIGBUS;
    	/* If the PMD would cover blocks out of the file */
    	if ((pgoff | PG_PMD_COLOUR) >= size) {
    		dax_pmd_dbg(NULL, address,
    				"offset + huge page size > file size");
    		return VM_FAULT_FALLBACK;
    	}
    
    	memset(&bh, 0, sizeof(bh));
    	bh.b_bdev = inode->i_sb->s_bdev;
    	block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);