Re: vfsmount lock issues on very large ppc64 box

From: Al Viro
Date: Mon Jul 18 2011 - 11:52:09 EST

On Mon, Jul 18, 2011 at 11:40:08AM -0400, Christoph Hellwig wrote:
> On Mon, Jul 18, 2011 at 10:17:08AM +0200, Eric Dumazet wrote:
> > > Tim posted a patch, but it wasn't applied for unknown reasons.
> > >
> > >
> > >
> >
> > Could Tim respin his patch then ?
> Btw, it seems like most kern_mount users want this and he's still
> missing some like devtmpfs, sysfs or ipc. What about splitting
> kern_mount into a variant that gets a long-term reference for these
> callers, and one that doesn't for afs/cifs/nfs automounts?

Careful - we need to balance that on shutdown side with
mnt_make_shortterm() before the final mntput()... Making it too
easy just on the kern_mount side will lead to easy-to-miss bugs.
For one thing, it's visible only on SMP boxen; for another there's
a lot of such internal vfsmounts (pipefs, sockets, etc.) that
are never shut down, so there'll be no easily copied examples of
what should not be forgotten on __exit side of things in obvious

FWIW, I had missed the original posting back in April - had been
without net.access then and it hadn't been resent when I came back, asked
people to resend the important ones and shitcanned the huge pile of pending
mail from the previous month...
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