investigation of Giant usage in kernel

[Divacky Roman]

hi

I looked at where Giant is held in the kernel and I found these interesting things:

1) in fs/fifofs/fifo_vnops.c we lock Giant when calling sorecieve()/sosend()
this is a bandaid for fixing a race that doesnt have to exist anymore. ie.
it needs some testing and can be remvoed

2) in geom/geom_dev.c we lock Giant for:

	2a) calling make_dev() which seems unecessary because make_dev protects
	    itself with devmtx
	2b) setting a flag in cdev which I think is unecessary as well

3) in kern/kern_descrip.c we lock Giant for the whole life of flock() I dont see
a need for this protection becuase

	3a) access to fp is protected with FILE_LOCK()ing
	3b) otherwise it operates on local variables
	3c) it also calls VOP_* functions but those dont require Giant, right?

4) in kern/kern_lockf.c we lock Giant for the whole life of lf_advlock() I dont
think this is necessary because
	
	4a) it operates on local variables
	4b) it calls various lf_*lock() functions which seems to either protect
	    themselves or not needed protection at all

5) in kern/kern_time.c we lock Giant to protect
	
	5a) tc_setclock() call - I dont know if this is necessary or not
	5b) lease_updatetime call which is a function pointer that seems to be
	    only assigned at one place (line 119 in kern_time.c) to a NOP function.
	    can this be removed?

6) in vm/device_pager.c we lock Giant to (also) protect cdevsw->d_mmap but the device mmap
is either MPSAFE or assigned to giant_mmap (a wrapper that locks GIant and calls the original
d_mmap) so this seems unecessary.

These are just my impressions on the code and I'd like to hear some comments if its correct and if its
I'd like to see some fixes.

thnx

roman