fix deadlock between msl_flush() and msl_write() when msl_flush() holds the mfh_lock for its duration then msl_write() tries to complete_fsrq(), which tries to get mfh_lock, by having msl_flush() not hold the mfh_lock.  it already does honors the rwlock for the bmap walk so this should be safe
fix deadlock between msl_flush() and msl_write() when msl_flush() holds the mfh_lock for its duration then msl_write() tries to complete_fsrq(), which tries to get mfh_lock, by having msl_flush() not hold the mfh_lock.  it already does honors the rwlock for the bmap walk so this should be safe

pscedu/slash2-stable,pscedu/slash2-stable,pscedu/slash2-stable,pscedu/slash2-stable,pscedu/slash2-stable,pscedu/slash2-stable,pscedu/slash2-stable