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Revision 7fb5409df092589b86cc9412d926879cb572b7f0 authored by Jan Kara on 10 February 2008, 06:08:38 UTC, committed by Theodore Ts'o on 10 February 2008, 06:08:38 UTC 
ext4: Fix Direct I/O locking
 
We cannot start transaction in ext4_direct_IO() and just let it last
during the whole write because dio_get_page() acquires mmap_sem which
ranks above transaction start (e.g. because we have dependency chain
mmap_sem->PageLock->journal_start, or because we update atime while
holding mmap_sem) and thus deadlocks could happen. We solve the problem
by starting a transaction separately for each ext4_get_block() call.

We *could* have a problem that we allocate a block and before its data
are written out the machine crashes and thus we expose stale data. But
that does not happen because for hole-filling generic code falls back to
buffered writes and for file extension, we add inode to orphan list and
thus in case of crash, journal replay will truncate inode back to the
original size.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
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Raw File
stack.c 
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/fs_stack.h>

/* does _NOT_ require i_mutex to be held.
 *
 * This function cannot be inlined since i_size_{read,write} is rather
 * heavy-weight on 32-bit systems
 */
void fsstack_copy_inode_size(struct inode *dst, const struct inode *src)
{
	i_size_write(dst, i_size_read((struct inode *)src));
	dst->i_blocks = src->i_blocks;
}
EXPORT_SYMBOL_GPL(fsstack_copy_inode_size);

/* copy all attributes; get_nlinks is optional way to override the i_nlink
 * copying
 */
void fsstack_copy_attr_all(struct inode *dest, const struct inode *src,
				int (*get_nlinks)(struct inode *))
{
	dest->i_mode = src->i_mode;
	dest->i_uid = src->i_uid;
	dest->i_gid = src->i_gid;
	dest->i_rdev = src->i_rdev;
	dest->i_atime = src->i_atime;
	dest->i_mtime = src->i_mtime;
	dest->i_ctime = src->i_ctime;
	dest->i_blkbits = src->i_blkbits;
	dest->i_flags = src->i_flags;

	/*
	 * Update the nlinks AFTER updating the above fields, because the
	 * get_links callback may depend on them.
	 */
	if (!get_nlinks)
		dest->i_nlink = src->i_nlink;
	else
		dest->i_nlink = (*get_nlinks)(dest);
}
EXPORT_SYMBOL_GPL(fsstack_copy_attr_all);
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