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SubjectRe: processes hung after sys_renameat, and 'missing' processes
On Mon, Jun 04, 2012 at 12:28:20AM +0100, Al Viro wrote:
> On Mon, Jun 04, 2012 at 12:17:09AM +0100, Al Viro wrote:
> >
> > > Also, sysrq-w is usually way more interesting than 't' when there are
> > > processes stuck on a mutex.
> > >
> > > Because yes, it looks like you have a boattload of trinity processes
> > > stuck on an inode mutex. Looks like every single one of them is in
> > > 'lock_rename()'. It *shouldn't* be an ABBA deadlock, since lockdep
> > > should have noticed that, but who knows.
> >
> > lock_rename() is a bit of a red herring here - they appear to be all
> > within-directory renames, so it's just a "trying to rename something
> > in a directory that has ->i_mutex held by something else".
> >
> > IOW, something else in there is holding ->i_mutex - something that
> > either hadn't been through lock_rename() at all or has already
> > passed through it and still hadn't got around to unlock_rename().
> > In either case, suspects won't have lock_rename() in the trace...
>
> Everything in lock_rename() appears to be at lock_rename+0x3e. Unless
> there's a really huge amount of filesystems on that box, this has to
> be
> mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
> and everything on that sucker is not holding any locks yet. IOW, that's
> the tail hanging off whatever deadlock is there.
>
> One possibility is that something has left the kernel without releasing
> i_mutex on some directory, which would make atomic_open patches the most
> obvious suspects.
>
> Which kernel it is and what filesystems are there? Is there nfsd anywhere
> in the mix?

Linus tree as of rc1, with 5ceb9ce6fe94 reverted, and a bunch of patches to
shut up noisy printk's that get spewed during fuzz testing.

No active nfs exports/mounts, though something caused nfsd.ko to get loaded
at some point (module use count of 13, weird).

Dave



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