Re: [RFC PATCH 0/6] Convert all tasklets to workqueues

[Roland Dreier <rdreier@cisco.com>]

 > > [ and on a similar notion, i still havent given up on seeing all BKL 
 > >   use gone from the kernel. I expect it to happen any decade now ;-) ]

 > 2.6.21 had 476 lock_kernel() calls. 2.6.22-git has 473 lock_kernel() 
 > calls currently. With that kind of flux we'll see the BKL gone in about 
 > 40 years =B-)

 > 'struct semaphore' use on the other hand has gone down by 10% in this 
 > release, which is a good rate. I guess the lack of lockdep coverage for 
 > semaphores might be one of the driving forces? ;-)

The problem with removing uses of the BKL is that a "lock_kernel()"
gives no clue about what it is protecting against, and so it requires
a lot of very difficult auditing to replace with appropriate locking.

To take a couple of examples at random: fs/ext4/ioctl.c takes the BKL
in ext4_compat_ioctl() around the call to ext4_ioctl().  Kind of sad
that a "next-generation" FS still uses the BKL, but who understands
things well enough to say how all the cases in ext4_ioctl() are
relying on being called with the BKL held?

As a second example, msr_seek() in arch/i386/kernel/msr.c... is the
inode semaphore enough or not?  Who understands the implications well
enough to say?

Most semaphores on the other hand can be replaced by mutexes or
completions in a fairly straightforward way.

 - R.