kernel - Hold vm_token() for certain buf/bio/vm_page interactions
* Hold the vm_token when messing around with page valid and dirty bits
in buffer cache operations. Such race conditions are possible but would
be very rare.
* Fix inconsistent use of bio2.bio_offset when swapcache intercepts an
I/O operation. When this case occurs the normal filesystem VOP_STRATEGY
function will not be called and any assumption that bio2.bio_offset
will represent a block device offset will be invalid.
To deal with this case swapcache will re-set bio_offset to NOOFFSET.
Filesystems use this value to determine that no block device offset
has been cached for a logical file block.
Reported-by: Jan Lentfer <Jan.Lentfer@web.de> (bio_offset issue)