Re: CVS commit: src/sys/ufs/ufs

[Antti Kantee <pooka%cs.hut.fi@localhost>]

On Tue May 25 2010 at 15:55:35 +0200, Alan Barrett wrote:
> On Tue, 25 May 2010, Antti Kantee wrote:
> > Modified Files:
> >     src/sys/ufs/ufs: ufs_wapbl.c
> > 
> > Log Message:
> > Add a comment describing an observed boom-crash-burn problem in
> > the code.  Fixing it will require a full tank of gas, half a pack
> > of cigarettes, sunglasses, darkness, and most importantly:
> > someone else.
> 
> What would I have to do from userland to tickle this bug?

You need to unlink and create a file after the first namei in sys_rename
but before VOP_RENAME runs, i.e. trigger a race condition.

Running tests/fs/ffs/t_renamerace a few times should suffice.  It uses
rump, so your host is safe.  If you have a uniprocessor host, set
RUMP_NCPU to 2 to have both threads run in the rump kernel in parallel
(well, they run "virtually parallel" on a uniprocessor system, but YKWIM).
This makes the race more likely to trigger.