Commit 3eaf9cc6 authored by Matthew Bobrowski's avatar Matthew Bobrowski Committed by Theodore Ts'o
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ext4: update ext4_sync_file() to not use __generic_file_fsync() 



When the filesystem is created without a journal, we eventually call
into __generic_file_fsync() in order to write out all the modified
in-core data to the permanent storage device. This function happens to
try and obtain an inode_lock() while synchronizing the files buffer
and it's associated metadata.

Generally, this is fine, however it becomes a problem when there is
higher level code that has already obtained an inode_lock() as this
leads to a recursive lock situation. This case is especially true when
porting across direct I/O to iomap infrastructure as we obtain an
inode_lock() early on in the I/O within ext4_dio_write_iter() and hold
it until the I/O has been completed. Consequently, to not run into
this specific issue, we move away from calling into
__generic_file_fsync() and perform the necessary synchronization tasks
within ext4_sync_file().

Signed-off-by: default avatarMatthew Bobrowski <mbobrowski@mbobrowski.org>
Reviewed-by: default avatarRitesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/3495f35ef67f2021b567e28e6f59222e583689b8.1572949325.git.mbobrowski@mbobrowski.org


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 0b9f230b

fs/ext4/fsync.c

+47 −25
Original line number Diff line number Diff line
@@ -80,6 +80,43 @@ static int ext4_sync_parent(struct inode *inode) 
	return ret;

}



static int ext4_fsync_nojournal(struct inode *inode, bool datasync,

				bool *needs_barrier)

{

	int ret, err;



	ret = sync_mapping_buffers(inode->i_mapping);

	if (!(inode->i_state & I_DIRTY_ALL))

		return ret;

	if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))

		return ret;



	err = sync_inode_metadata(inode, 1);

	if (!ret)

		ret = err;



	if (!ret)

		ret = ext4_sync_parent(inode);

	if (test_opt(inode->i_sb, BARRIER))

		*needs_barrier = true;



	return ret;

}



static int ext4_fsync_journal(struct inode *inode, bool datasync,

			     bool *needs_barrier)

{

	struct ext4_inode_info *ei = EXT4_I(inode);

	journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;

	tid_t commit_tid = datasync ? ei->i_datasync_tid : ei->i_sync_tid;



	if (journal->j_flags & JBD2_BARRIER &&

	    !jbd2_trans_will_send_data_barrier(journal, commit_tid))

		*needs_barrier = true;



	return jbd2_complete_transaction(journal, commit_tid);

}



/*

 * akpm: A new design for ext4_sync_file().

 *
@@ -91,17 +128,14 @@ static int ext4_sync_parent(struct inode *inode) 
 * What we do is just kick off a commit and wait on it.  This will snapshot the

 * inode to disk.

 */



int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)

{

	struct inode *inode = file->f_mapping->host;

	struct ext4_inode_info *ei = EXT4_I(inode);

	journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;

	int ret = 0, err;

	tid_t commit_tid;

	bool needs_barrier = false;

	struct inode *inode = file->f_mapping->host;

	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);



	if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))

	if (unlikely(ext4_forced_shutdown(sbi)))

		return -EIO;



	J_ASSERT(ext4_journal_current_handle() == NULL);
@@ -111,23 +145,15 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync) 
	if (sb_rdonly(inode->i_sb)) {

		/* Make sure that we read updated s_mount_flags value */

		smp_rmb();

		if (EXT4_SB(inode->i_sb)->s_mount_flags & EXT4_MF_FS_ABORTED)

		if (sbi->s_mount_flags & EXT4_MF_FS_ABORTED)

			ret = -EROFS;

		goto out;

	}



	if (!journal) {

		ret = __generic_file_fsync(file, start, end, datasync);

		if (!ret)

			ret = ext4_sync_parent(inode);

		if (test_opt(inode->i_sb, BARRIER))

			goto issue_flush;

		goto out;

	}



	ret = file_write_and_wait_range(file, start, end);

	if (ret)

		return ret;



	/*

	 * data=writeback,ordered:

	 *  The caller's filemap_fdatawrite()/wait will sync the data.
@@ -142,18 +168,14 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync) 
	 *  (they were dirtied by commit).  But that's OK - the blocks are

	 *  safe in-journal, which is all fsync() needs to ensure.

	 */

	if (ext4_should_journal_data(inode)) {

	if (!sbi->s_journal)

		ret = ext4_fsync_nojournal(inode, datasync, &needs_barrier);

	else if (ext4_should_journal_data(inode))

		ret = ext4_force_commit(inode->i_sb);

		goto out;

	}

	else

		ret = ext4_fsync_journal(inode, datasync, &needs_barrier);



	commit_tid = datasync ? ei->i_datasync_tid : ei->i_sync_tid;

	if (journal->j_flags & JBD2_BARRIER &&

	    !jbd2_trans_will_send_data_barrier(journal, commit_tid))

		needs_barrier = true;

	ret = jbd2_complete_transaction(journal, commit_tid);

	if (needs_barrier) {

	issue_flush:

		err = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);

		if (!ret)

			ret = err;

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