Re: processes hung after sys_renameat, and 'missing' processes

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

On Sun, Jun 03, 2012 at 05:16:30PM -0700, Linus Torvalds wrote:
> On Sun, Jun 3, 2012 at 5:00 PM, Dave Jones <davej@redhat.com> wrote:
> >
> > sysrq-d: http://fpaste.org/ow9O/
> 
> Ugh. I'm adding PeterZ to the cc, just to see if he can make more sense of it.
> 
> Peter, is there no way to make the lock thing print not just the lock
> class name, but also the pointer to the actual *instance* of the lock
> held?
> 
> Also, it's a bit unclear to me, but I *think* that most of those users
> don't actually "hold" the lock - they are waiting for it. Yes/no?

Has to be, unless something _very_ odd is going on...  Just how many
->s_vfs_rename_mutex are there on that box?

> Does
> the lockdep information have the capability to distinguish between
> "waiting for" vs "actually successfully owns the lock"?

Another question re lockdep - does it scream loudly if process returns
to userland without having released some lock?  I hope so, but I've never
checked that... ;-/