![Dave Chinner](/assets/img/avatar_default.png)
When modifying the patch series to handle the XFS MMAP_LOCK nesting of page faults, I botched the conversion of the read page fault path, and so it is only every calling through the page cache. Re-add the necessary __dax_fault() call for such files. Because the get_blocks callback on read faults may not set up the mapping buffer correctly to allow unwritten extent completion to be run, we need to allow callers of __dax_fault() to pass a null complete_unwritten() callback. The DAX code always zeros the unwritten page when it is read faulted so there are no stale data exposure issues with not doing the conversion. The only downside will be the potential for increased CPU overhead on repeated read faults of the same page. If this proves to be a problem, then the filesystem needs to fix it's get_block callback and provide a convert_unwritten() callback to the read fault path. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Matthew Wilcox <willy@linux.intel.com> Reviewed-by: Brian Foster <bfoster@redhat.com> Signed-off-by: Dave Chinner <david@fromorbit.com>
583 lines
17 KiB
C
583 lines
17 KiB
C
/*
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* fs/dax.c - Direct Access filesystem code
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* Copyright (c) 2013-2014 Intel Corporation
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* Author: Matthew Wilcox <matthew.r.wilcox@intel.com>
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* Author: Ross Zwisler <ross.zwisler@linux.intel.com>
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms and conditions of the GNU General Public License,
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* version 2, as published by the Free Software Foundation.
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*
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* This program is distributed in the hope it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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* more details.
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*/
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#include <linux/atomic.h>
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#include <linux/blkdev.h>
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#include <linux/buffer_head.h>
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#include <linux/fs.h>
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#include <linux/genhd.h>
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#include <linux/highmem.h>
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#include <linux/memcontrol.h>
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#include <linux/mm.h>
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#include <linux/mutex.h>
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#include <linux/sched.h>
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#include <linux/uio.h>
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#include <linux/vmstat.h>
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int dax_clear_blocks(struct inode *inode, sector_t block, long size)
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{
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struct block_device *bdev = inode->i_sb->s_bdev;
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sector_t sector = block << (inode->i_blkbits - 9);
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might_sleep();
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do {
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void *addr;
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unsigned long pfn;
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long count;
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count = bdev_direct_access(bdev, sector, &addr, &pfn, size);
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if (count < 0)
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return count;
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BUG_ON(size < count);
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while (count > 0) {
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unsigned pgsz = PAGE_SIZE - offset_in_page(addr);
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if (pgsz > count)
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pgsz = count;
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if (pgsz < PAGE_SIZE)
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memset(addr, 0, pgsz);
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else
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clear_page(addr);
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addr += pgsz;
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size -= pgsz;
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count -= pgsz;
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BUG_ON(pgsz & 511);
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sector += pgsz / 512;
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cond_resched();
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}
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} while (size);
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return 0;
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}
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EXPORT_SYMBOL_GPL(dax_clear_blocks);
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static long dax_get_addr(struct buffer_head *bh, void **addr, unsigned blkbits)
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{
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unsigned long pfn;
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sector_t sector = bh->b_blocknr << (blkbits - 9);
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return bdev_direct_access(bh->b_bdev, sector, addr, &pfn, bh->b_size);
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}
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static void dax_new_buf(void *addr, unsigned size, unsigned first, loff_t pos,
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loff_t end)
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{
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loff_t final = end - pos + first; /* The final byte of the buffer */
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if (first > 0)
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memset(addr, 0, first);
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if (final < size)
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memset(addr + final, 0, size - final);
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}
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static bool buffer_written(struct buffer_head *bh)
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{
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return buffer_mapped(bh) && !buffer_unwritten(bh);
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}
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/*
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* When ext4 encounters a hole, it returns without modifying the buffer_head
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* which means that we can't trust b_size. To cope with this, we set b_state
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* to 0 before calling get_block and, if any bit is set, we know we can trust
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* b_size. Unfortunate, really, since ext4 knows precisely how long a hole is
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* and would save us time calling get_block repeatedly.
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*/
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static bool buffer_size_valid(struct buffer_head *bh)
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{
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return bh->b_state != 0;
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}
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static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
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loff_t start, loff_t end, get_block_t get_block,
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struct buffer_head *bh)
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{
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ssize_t retval = 0;
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loff_t pos = start;
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loff_t max = start;
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loff_t bh_max = start;
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void *addr;
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bool hole = false;
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if (iov_iter_rw(iter) != WRITE)
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end = min(end, i_size_read(inode));
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while (pos < end) {
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unsigned len;
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if (pos == max) {
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unsigned blkbits = inode->i_blkbits;
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sector_t block = pos >> blkbits;
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unsigned first = pos - (block << blkbits);
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long size;
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if (pos == bh_max) {
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bh->b_size = PAGE_ALIGN(end - pos);
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bh->b_state = 0;
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retval = get_block(inode, block, bh,
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iov_iter_rw(iter) == WRITE);
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if (retval)
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break;
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if (!buffer_size_valid(bh))
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bh->b_size = 1 << blkbits;
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bh_max = pos - first + bh->b_size;
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} else {
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unsigned done = bh->b_size -
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(bh_max - (pos - first));
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bh->b_blocknr += done >> blkbits;
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bh->b_size -= done;
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}
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hole = iov_iter_rw(iter) != WRITE && !buffer_written(bh);
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if (hole) {
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addr = NULL;
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size = bh->b_size - first;
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} else {
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retval = dax_get_addr(bh, &addr, blkbits);
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if (retval < 0)
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break;
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if (buffer_unwritten(bh) || buffer_new(bh))
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dax_new_buf(addr, retval, first, pos,
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end);
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addr += first;
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size = retval - first;
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}
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max = min(pos + size, end);
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}
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if (iov_iter_rw(iter) == WRITE)
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len = copy_from_iter_nocache(addr, max - pos, iter);
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else if (!hole)
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len = copy_to_iter(addr, max - pos, iter);
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else
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len = iov_iter_zero(max - pos, iter);
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if (!len)
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break;
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pos += len;
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addr += len;
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}
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return (pos == start) ? retval : pos - start;
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}
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/**
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* dax_do_io - Perform I/O to a DAX file
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* @iocb: The control block for this I/O
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* @inode: The file which the I/O is directed at
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* @iter: The addresses to do I/O from or to
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* @pos: The file offset where the I/O starts
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* @get_block: The filesystem method used to translate file offsets to blocks
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* @end_io: A filesystem callback for I/O completion
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* @flags: See below
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*
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* This function uses the same locking scheme as do_blockdev_direct_IO:
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* If @flags has DIO_LOCKING set, we assume that the i_mutex is held by the
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* caller for writes. For reads, we take and release the i_mutex ourselves.
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* If DIO_LOCKING is not set, the filesystem takes care of its own locking.
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* As with do_blockdev_direct_IO(), we increment i_dio_count while the I/O
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* is in progress.
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*/
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ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
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struct iov_iter *iter, loff_t pos, get_block_t get_block,
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dio_iodone_t end_io, int flags)
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{
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struct buffer_head bh;
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ssize_t retval = -EINVAL;
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loff_t end = pos + iov_iter_count(iter);
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memset(&bh, 0, sizeof(bh));
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if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ) {
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struct address_space *mapping = inode->i_mapping;
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mutex_lock(&inode->i_mutex);
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retval = filemap_write_and_wait_range(mapping, pos, end - 1);
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if (retval) {
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mutex_unlock(&inode->i_mutex);
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goto out;
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}
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}
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/* Protects against truncate */
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if (!(flags & DIO_SKIP_DIO_COUNT))
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inode_dio_begin(inode);
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retval = dax_io(inode, iter, pos, end, get_block, &bh);
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if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
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mutex_unlock(&inode->i_mutex);
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if ((retval > 0) && end_io)
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end_io(iocb, pos, retval, bh.b_private);
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if (!(flags & DIO_SKIP_DIO_COUNT))
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inode_dio_end(inode);
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out:
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return retval;
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}
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EXPORT_SYMBOL_GPL(dax_do_io);
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/*
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* The user has performed a load from a hole in the file. Allocating
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* a new page in the file would cause excessive storage usage for
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* workloads with sparse files. We allocate a page cache page instead.
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* We'll kick it out of the page cache if it's ever written to,
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* otherwise it will simply fall out of the page cache under memory
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* pressure without ever having been dirtied.
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*/
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static int dax_load_hole(struct address_space *mapping, struct page *page,
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struct vm_fault *vmf)
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{
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unsigned long size;
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struct inode *inode = mapping->host;
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if (!page)
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page = find_or_create_page(mapping, vmf->pgoff,
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GFP_KERNEL | __GFP_ZERO);
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if (!page)
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return VM_FAULT_OOM;
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/* Recheck i_size under page lock to avoid truncate race */
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size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
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if (vmf->pgoff >= size) {
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unlock_page(page);
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page_cache_release(page);
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return VM_FAULT_SIGBUS;
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}
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vmf->page = page;
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return VM_FAULT_LOCKED;
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}
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static int copy_user_bh(struct page *to, struct buffer_head *bh,
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unsigned blkbits, unsigned long vaddr)
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{
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void *vfrom, *vto;
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if (dax_get_addr(bh, &vfrom, blkbits) < 0)
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return -EIO;
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vto = kmap_atomic(to);
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copy_user_page(vto, vfrom, vaddr, to);
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kunmap_atomic(vto);
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return 0;
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}
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static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
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struct vm_area_struct *vma, struct vm_fault *vmf)
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{
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struct address_space *mapping = inode->i_mapping;
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sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);
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unsigned long vaddr = (unsigned long)vmf->virtual_address;
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void *addr;
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unsigned long pfn;
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pgoff_t size;
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int error;
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i_mmap_lock_read(mapping);
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/*
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* Check truncate didn't happen while we were allocating a block.
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* If it did, this block may or may not be still allocated to the
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* file. We can't tell the filesystem to free it because we can't
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* take i_mutex here. In the worst case, the file still has blocks
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* allocated past the end of the file.
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*/
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size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
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if (unlikely(vmf->pgoff >= size)) {
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error = -EIO;
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goto out;
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}
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error = bdev_direct_access(bh->b_bdev, sector, &addr, &pfn, bh->b_size);
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if (error < 0)
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goto out;
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if (error < PAGE_SIZE) {
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error = -EIO;
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goto out;
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}
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if (buffer_unwritten(bh) || buffer_new(bh))
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clear_page(addr);
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error = vm_insert_mixed(vma, vaddr, pfn);
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out:
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i_mmap_unlock_read(mapping);
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return error;
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}
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/**
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* __dax_fault - handle a page fault on a DAX file
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* @vma: The virtual memory area where the fault occurred
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* @vmf: The description of the fault
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* @get_block: The filesystem method used to translate file offsets to blocks
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* @complete_unwritten: The filesystem method used to convert unwritten blocks
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* to written so the data written to them is exposed. This is required for
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* required by write faults for filesystems that will return unwritten
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* extent mappings from @get_block, but it is optional for reads as
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* dax_insert_mapping() will always zero unwritten blocks. If the fs does
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* not support unwritten extents, the it should pass NULL.
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*
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* When a page fault occurs, filesystems may call this helper in their
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* fault handler for DAX files. __dax_fault() assumes the caller has done all
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* the necessary locking for the page fault to proceed successfully.
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*/
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int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
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get_block_t get_block, dax_iodone_t complete_unwritten)
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{
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struct file *file = vma->vm_file;
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struct address_space *mapping = file->f_mapping;
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struct inode *inode = mapping->host;
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struct page *page;
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struct buffer_head bh;
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unsigned long vaddr = (unsigned long)vmf->virtual_address;
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unsigned blkbits = inode->i_blkbits;
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sector_t block;
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pgoff_t size;
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int error;
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int major = 0;
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size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
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if (vmf->pgoff >= size)
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return VM_FAULT_SIGBUS;
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memset(&bh, 0, sizeof(bh));
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block = (sector_t)vmf->pgoff << (PAGE_SHIFT - blkbits);
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bh.b_size = PAGE_SIZE;
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repeat:
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page = find_get_page(mapping, vmf->pgoff);
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if (page) {
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if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags)) {
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page_cache_release(page);
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return VM_FAULT_RETRY;
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}
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if (unlikely(page->mapping != mapping)) {
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unlock_page(page);
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page_cache_release(page);
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goto repeat;
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}
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size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
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if (unlikely(vmf->pgoff >= size)) {
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/*
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* We have a struct page covering a hole in the file
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* from a read fault and we've raced with a truncate
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*/
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error = -EIO;
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goto unlock_page;
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}
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}
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error = get_block(inode, block, &bh, 0);
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if (!error && (bh.b_size < PAGE_SIZE))
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error = -EIO; /* fs corruption? */
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if (error)
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goto unlock_page;
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if (!buffer_mapped(&bh) && !buffer_unwritten(&bh) && !vmf->cow_page) {
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if (vmf->flags & FAULT_FLAG_WRITE) {
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error = get_block(inode, block, &bh, 1);
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count_vm_event(PGMAJFAULT);
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mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
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major = VM_FAULT_MAJOR;
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if (!error && (bh.b_size < PAGE_SIZE))
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error = -EIO;
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if (error)
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goto unlock_page;
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} else {
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return dax_load_hole(mapping, page, vmf);
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}
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}
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if (vmf->cow_page) {
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struct page *new_page = vmf->cow_page;
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if (buffer_written(&bh))
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error = copy_user_bh(new_page, &bh, blkbits, vaddr);
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else
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clear_user_highpage(new_page, vaddr);
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if (error)
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goto unlock_page;
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vmf->page = page;
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if (!page) {
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i_mmap_lock_read(mapping);
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/* Check we didn't race with truncate */
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size = (i_size_read(inode) + PAGE_SIZE - 1) >>
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PAGE_SHIFT;
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if (vmf->pgoff >= size) {
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i_mmap_unlock_read(mapping);
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error = -EIO;
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goto out;
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}
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}
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return VM_FAULT_LOCKED;
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}
|
|
|
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/* Check we didn't race with a read fault installing a new page */
|
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if (!page && major)
|
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page = find_lock_page(mapping, vmf->pgoff);
|
|
|
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if (page) {
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unmap_mapping_range(mapping, vmf->pgoff << PAGE_SHIFT,
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PAGE_CACHE_SIZE, 0);
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delete_from_page_cache(page);
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unlock_page(page);
|
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page_cache_release(page);
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}
|
|
|
|
/*
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* If we successfully insert the new mapping over an unwritten extent,
|
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* we need to ensure we convert the unwritten extent. If there is an
|
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* error inserting the mapping, the filesystem needs to leave it as
|
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* unwritten to prevent exposure of the stale underlying data to
|
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* userspace, but we still need to call the completion function so
|
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* the private resources on the mapping buffer can be released. We
|
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* indicate what the callback should do via the uptodate variable, same
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* as for normal BH based IO completions.
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*/
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error = dax_insert_mapping(inode, &bh, vma, vmf);
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if (buffer_unwritten(&bh)) {
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if (complete_unwritten)
|
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complete_unwritten(&bh, !error);
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else
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WARN_ON_ONCE(!(vmf->flags & FAULT_FLAG_WRITE));
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|
}
|
|
|
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out:
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if (error == -ENOMEM)
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return VM_FAULT_OOM | major;
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/* -EBUSY is fine, somebody else faulted on the same PTE */
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if ((error < 0) && (error != -EBUSY))
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return VM_FAULT_SIGBUS | major;
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return VM_FAULT_NOPAGE | major;
|
|
|
|
unlock_page:
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if (page) {
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unlock_page(page);
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page_cache_release(page);
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}
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goto out;
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}
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|
EXPORT_SYMBOL(__dax_fault);
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|
|
|
/**
|
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* dax_fault - handle a page fault on a DAX file
|
|
* @vma: The virtual memory area where the fault occurred
|
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* @vmf: The description of the fault
|
|
* @get_block: The filesystem method used to translate file offsets to blocks
|
|
*
|
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* When a page fault occurs, filesystems may call this helper in their
|
|
* fault handler for DAX files.
|
|
*/
|
|
int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
|
|
get_block_t get_block, dax_iodone_t complete_unwritten)
|
|
{
|
|
int result;
|
|
struct super_block *sb = file_inode(vma->vm_file)->i_sb;
|
|
|
|
if (vmf->flags & FAULT_FLAG_WRITE) {
|
|
sb_start_pagefault(sb);
|
|
file_update_time(vma->vm_file);
|
|
}
|
|
result = __dax_fault(vma, vmf, get_block, complete_unwritten);
|
|
if (vmf->flags & FAULT_FLAG_WRITE)
|
|
sb_end_pagefault(sb);
|
|
|
|
return result;
|
|
}
|
|
EXPORT_SYMBOL_GPL(dax_fault);
|
|
|
|
/**
|
|
* dax_pfn_mkwrite - handle first write to DAX page
|
|
* @vma: The virtual memory area where the fault occurred
|
|
* @vmf: The description of the fault
|
|
*
|
|
*/
|
|
int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
|
|
{
|
|
struct super_block *sb = file_inode(vma->vm_file)->i_sb;
|
|
|
|
sb_start_pagefault(sb);
|
|
file_update_time(vma->vm_file);
|
|
sb_end_pagefault(sb);
|
|
return VM_FAULT_NOPAGE;
|
|
}
|
|
EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
|
|
|
|
/**
|
|
* dax_zero_page_range - zero a range within a page of a DAX file
|
|
* @inode: The file being truncated
|
|
* @from: The file offset that is being truncated to
|
|
* @length: The number of bytes to zero
|
|
* @get_block: The filesystem method used to translate file offsets to blocks
|
|
*
|
|
* This function can be called by a filesystem when it is zeroing part of a
|
|
* page in a DAX file. This is intended for hole-punch operations. If
|
|
* you are truncating a file, the helper function dax_truncate_page() may be
|
|
* more convenient.
|
|
*
|
|
* We work in terms of PAGE_CACHE_SIZE here for commonality with
|
|
* block_truncate_page(), but we could go down to PAGE_SIZE if the filesystem
|
|
* took care of disposing of the unnecessary blocks. Even if the filesystem
|
|
* block size is smaller than PAGE_SIZE, we have to zero the rest of the page
|
|
* since the file might be mmapped.
|
|
*/
|
|
int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
|
|
get_block_t get_block)
|
|
{
|
|
struct buffer_head bh;
|
|
pgoff_t index = from >> PAGE_CACHE_SHIFT;
|
|
unsigned offset = from & (PAGE_CACHE_SIZE-1);
|
|
int err;
|
|
|
|
/* Block boundary? Nothing to do */
|
|
if (!length)
|
|
return 0;
|
|
BUG_ON((offset + length) > PAGE_CACHE_SIZE);
|
|
|
|
memset(&bh, 0, sizeof(bh));
|
|
bh.b_size = PAGE_CACHE_SIZE;
|
|
err = get_block(inode, index, &bh, 0);
|
|
if (err < 0)
|
|
return err;
|
|
if (buffer_written(&bh)) {
|
|
void *addr;
|
|
err = dax_get_addr(&bh, &addr, inode->i_blkbits);
|
|
if (err < 0)
|
|
return err;
|
|
memset(addr + offset, 0, length);
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
EXPORT_SYMBOL_GPL(dax_zero_page_range);
|
|
|
|
/**
|
|
* dax_truncate_page - handle a partial page being truncated in a DAX file
|
|
* @inode: The file being truncated
|
|
* @from: The file offset that is being truncated to
|
|
* @get_block: The filesystem method used to translate file offsets to blocks
|
|
*
|
|
* Similar to block_truncate_page(), this function can be called by a
|
|
* filesystem when it is truncating a DAX file to handle the partial page.
|
|
*
|
|
* We work in terms of PAGE_CACHE_SIZE here for commonality with
|
|
* block_truncate_page(), but we could go down to PAGE_SIZE if the filesystem
|
|
* took care of disposing of the unnecessary blocks. Even if the filesystem
|
|
* block size is smaller than PAGE_SIZE, we have to zero the rest of the page
|
|
* since the file might be mmapped.
|
|
*/
|
|
int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
|
|
{
|
|
unsigned length = PAGE_CACHE_ALIGN(from) - from;
|
|
return dax_zero_page_range(inode, from, length, get_block);
|
|
}
|
|
EXPORT_SYMBOL_GPL(dax_truncate_page);
|