cvs commit: src/sys/fs/devfs devfs_vnops.c src/sys/fs/fifofs fifo_vnops.c src/sys/kern uipc_usrreq.c vfs_vnops.c src/sys/vm vnode_pager.c

[John Baldwin]

On Wednesday 03 October 2007 07:48:00 pm Jeff Roberson wrote:
> On Wed, 3 Oct 2007, John Baldwin wrote:
> 
> > jhb         2007-10-03 21:06:05 UTC
> >
> >  FreeBSD src repository
> >
> >  Modified files:        (Branch: RELENG_6)
> >    sys/fs/devfs         devfs_vnops.c
> >    sys/fs/fifofs        fifo_vnops.c
> >    sys/kern             uipc_usrreq.c vfs_vnops.c
> >    sys/vm               vnode_pager.c
> >  Log:
> >  MFC: Always use an exclusive lock on the leaf vnode during an open() when
> >  shared lookups are enabled.  This closes a few races including a race 
where
> >  concurrent opens of a fifo could result in different v_fifoinfo 
structures
> >  in different threads.
> 
> Long term we should really look for a better solution to this problem. 
> There are a number of was to improve snapshots in ffs by fixing shared 
> locking.

I don't disagree.  The fifo case can be fixed easily enough in the fifo code 
by using fifo_mtx to protect v_fifoinfo perhaps (or doing an upgrade on the 
vnode lock?), but for the MFC I didn't want to have to fix each of the races 
with open(2).  Probably better to fix it more properly in HEAD first.

-- 
John Baldwin