ext4: serialize truncate with owerwrite DIO workers
Jan Kara have spotted interesting issue: There are potential data corruption issue with direct IO overwrites racing with truncate: Like: dio write truncate_task ->ext4_ext_direct_IO ->overwrite == 1 ->down_read(&EXT4_I(inode)->i_data_sem); ->mutex_unlock(&inode->i_mutex); ->ext4_setattr() ->inode_dio_wait() ->truncate_setsize() ->ext4_truncate() ->down_write(&EXT4_I(inode)->i_data_sem); ->__blockdev_direct_IO ->ext4_get_block ->submit_io() ->up_read(&EXT4_I(inode)->i_data_sem); # truncate data blocks, allocate them to # other inode - bad stuff happens because # dio is still in flight. In order to serialize with truncate dio worker should grab extra i_dio_count reference before drop i_mutex. Reviewed-by: NJan Kara <jack@suse.cz> Signed-off-by: NDmitry Monakhov <dmonakhov@openvz.org> Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
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