Re: Does mandatory locking need to be set when the file is locked?

[Matthew Wilcox <willy@debian.org>]

On Mon, Dec 15, 2003 at 01:09:11PM -0500, Trond Myklebust wrote:
> Finally, the Linux mandatory locking implementation does not eliminate
> all possible races: currently there is no attempt made to exclude one
> thread from taking a lock while another is still in the process of
> writing to the file, or if it already has a section of that file
> mmapped. In that case, the lock call may well succeed, but the
> other thread that is inside read/write/mmap will not see it.
> 
> So if you want to DEPEND on mandatory locking to work, then you
> probably have some kernel debugging to do first.

And fixing these problems requires some pretty invasive work to
current hot code paths like read/write/mmap/open/close.  When I started
investigating it, I was told the additional overhead for my scheme was
unacceptable and to just forget about it because nobody really used
mandatory locks anyway.

That was enough to put me off.

-- 
"Next the statesmen will invent cheap lies, putting the blame upon 
the nation that is attacked, and every man will be glad of those
conscience-soothing falsities, and will diligently study them, and refuse
to examine any refutations of them; and thus he will by and by convince 
himself that the war is just, and will thank God for the better sleep 
he enjoys after this process of grotesque self-deception." -- Mark Twain