fs/locks.c BKL removal

[Dave Hansen <haveblue@us.ibm.com>]

Matthew,
Al Viro pointed me your way.

I'm looking into the fs/locks.c mess.  It appears that there was an 
attempt to convert this over to a semaphore, but it was removed just 
before the 2.4 release because of some deadlocks.

Whenever the i_flock list is traversed, the BKL is held.  It is also 
held while running through the file_lock_list which I think is used 
only for /proc/locks.

We definitely need a semaphore because of all the blocking that goes 
on.  We can either have a global lock for all of them, which I think 
was tried last time.  Or, we can split it up a bit more.  With the 
current design, there will need to be a lock for the global list, each 
individual list, and one for each individual lock to protect against 
access from the reference in the file_lock_list and the inode->i_flock 
list.

However, I think that the file_lock_list complexity may be able to be 
reduced.  If we make the file_lock_list a list of inodes (or just the 
i_flocks) with active locks, we can avoid the complexity of having an 
individual file_lock lock.  That way, we at least reduce the number of 
_types_ of locks.  It increases the number of dereferences, but this 
is /proc we're talking about.  Any comments?

Talking about locks for locks is confusing :)

-- 
Dave Hansen
haveblue@us.ibm.com