Hi Neil, all,

  The nfs daemons run holding the global kernel lock.  They still hold
this lock over calls to file_op's read and write.

  The file system kernel interface (FSKI) doesn't require the kernel lock
to be held over these read/write calls.  The nfs daemons do not require 
that the reads or writes do not block (would be v silly if they did), so
they have no guarantee the lock isn't dropped and retaken during
blocking.  ie. they aren't using it as a guard across the calls.

  Dropping the kernel lock around read and write in fs/nfsd/vfs.c is a
_big_ SMP scalability win!

  Attached patch is against 2.4.1-ac18, but should apply to most recent
kernel versions.

Mark