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Re: tstile syndrome

On Thu, Aug 27, 2009 at 01:09:16PM +0200, Manuel Bouyer wrote:

> Hi,
> here's what I found so far on a server that show the tstile hang,
> with some ddb+gdb playing.
> Most processes are waiting on a tunrstile (you did know that),
> the one I started with had more than 4000 writers in the queue.
> The threads did come here though a VOP_LOCK() (you did also know that).
> This is a tunrstile for a rwlock, I found the owner of this rwlock.
> This thread is also waiting on a turnstile, but a different one,
> it also did come here though a VOP_LOCK. This is also a turnstile for a
> rwlock, which also has a owner, which also has VOP_LOCK in his stack
> trace and is waiting on a turnstile. It's also a rwlock (I checked the
> l_syncobj) but l_wchan is bogus: ffff800079ac402f, this is not a
> valid krwlock_t* (and examining memory at this address doesn't look like
> a valid krwlock_t value, and 'show lock' doens't know about it either). 
> any idea where to go from here ?

Are you running nullfs?  I suspect that with layerfs there are lock leaks
and conditions where it continues to use another vnode's lock when that
vnode has been freed or recycled and gained another identity.  Yet another
reason take vnode locking to the dump, cue objection from Holland.

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