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ext4: fix races between buffered IO and collapse / insert range
Current code implementing FALLOC_FL_COLLAPSE_RANGE and FALLOC_FL_INSERT_RANGE is prone to races with buffered writes and page faults. If buffered write or write via mmap manages to squeeze between filemap_write_and_wait_range() and truncate_pagecache() in the fallocate implementations, the written data is simply discarded by truncate_pagecache() although it should have been shifted. Fix the problem by moving filemap_write_and_wait_range() call inside i_mutex and i_mmap_sem. That way we are protected against races with both buffered writes and page faults. Signed-off-by: Jan Kara <jack@suse.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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@ -5487,21 +5487,7 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
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return ret;
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}
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/*
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* Need to round down offset to be aligned with page size boundary
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* for page size > block size.
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*/
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ioffset = round_down(offset, PAGE_SIZE);
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/* Write out all dirty pages */
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ret = filemap_write_and_wait_range(inode->i_mapping, ioffset,
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LLONG_MAX);
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if (ret)
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return ret;
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/* Take mutex lock */
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mutex_lock(&inode->i_mutex);
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/*
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* There is no need to overlap collapse range with EOF, in which case
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* it is effectively a truncate operation
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@ -5526,6 +5512,27 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
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* page cache.
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*/
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down_write(&EXT4_I(inode)->i_mmap_sem);
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/*
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* Need to round down offset to be aligned with page size boundary
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* for page size > block size.
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*/
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ioffset = round_down(offset, PAGE_SIZE);
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/*
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* Write tail of the last page before removed range since it will get
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* removed from the page cache below.
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*/
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ret = filemap_write_and_wait_range(inode->i_mapping, ioffset, offset);
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if (ret)
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goto out_mmap;
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/*
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* Write data that will be shifted to preserve them when discarding
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* page cache below. We are also protected from pages becoming dirty
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* by i_mmap_sem.
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*/
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ret = filemap_write_and_wait_range(inode->i_mapping, offset + len,
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LLONG_MAX);
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if (ret)
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goto out_mmap;
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truncate_pagecache(inode, ioffset);
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credits = ext4_writepage_trans_blocks(inode);
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@ -5626,21 +5633,7 @@ int ext4_insert_range(struct inode *inode, loff_t offset, loff_t len)
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return ret;
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}
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/*
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* Need to round down to align start offset to page size boundary
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* for page size > block size.
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*/
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ioffset = round_down(offset, PAGE_SIZE);
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/* Write out all dirty pages */
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ret = filemap_write_and_wait_range(inode->i_mapping, ioffset,
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LLONG_MAX);
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if (ret)
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return ret;
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/* Take mutex lock */
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mutex_lock(&inode->i_mutex);
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/* Currently just for extent based files */
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if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
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ret = -EOPNOTSUPP;
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@ -5668,6 +5661,16 @@ int ext4_insert_range(struct inode *inode, loff_t offset, loff_t len)
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* page cache.
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*/
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down_write(&EXT4_I(inode)->i_mmap_sem);
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/*
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* Need to round down to align start offset to page size boundary
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* for page size > block size.
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*/
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ioffset = round_down(offset, PAGE_SIZE);
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/* Write out all dirty pages */
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ret = filemap_write_and_wait_range(inode->i_mapping, ioffset,
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LLONG_MAX);
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if (ret)
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goto out_mmap;
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truncate_pagecache(inode, ioffset);
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credits = ext4_writepage_trans_blocks(inode);
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