Re: [LTP/VFS] fcntl SETLEASE fails on ramfs/tmpfs

[Al Viro <viro@ZenIV.linux.org.uk>]

On Tue, Apr 29, 2008 at 05:42:31PM -0400, J. Bruce Fields wrote:
> The most likely consequences are that a local reader gets out-of-date
> data for a file that a Samba client has modified.
> 
> I suppose that re-checking the d_count and i_count after step 3 might
> close the race.
 
The hell it might.  Leases are broken, plain and simple.  Not to mention
anything else, a couple of threads with shared descriptor table will
bypass these checks happily.

FWIW, that's far from the worst problem in fs/locks.c, and not even the
worst one with leases.

That, BTW, is a fine demonstration of the reasons why application-specific
kernel warts(tm) are bad.  Lease support is samba-only turd; so's dnotify,
with its lovely problems.  And interfaces like that *suck*; they are
developed with one application in mind and that leads to "we know how it
will be used" mentality.  With obvious implications for quality of review
they get from their developers...

Al, currently crawling through struct file_lock review and extremely annoyed
by the amount of turds being found...