Subject: Re: deadlock with sched_lock in SA code
To: Nathan J. Williams <>
From: Eric Haszlakiewicz <>
List: tech-kern
Date: 08/28/2005 22:50:17
On Sun, Aug 28, 2005 at 10:35:04PM -0400, Nathan J. Williams wrote:
> YAMAMOTO Takashi <> writes:
> > > allocating pages from UVM can call wakeup(), so we must avoid that
> > > while holding sched_lock.  one way to do this would be to call
> > > sadata_upcall_alloc() before acquiring sched_lock and passing the
> > > resulting pointer to sa_switch(), instead of calling that in
> > > sa_switch() itself.  does anyone have any better suggestions?
> > > if not, I'll fix it that way.
> > > 
> > > -Chuck
> > 
> > i thought there were an effort to allocate upcall data on new lwp's stack.
> There was. I still have patches for that in one of my development
> trees. It kind of stalled out when I reached sparc/sparc64 and tried
> to wrap my head around how those stacks are handled.

	I think it'd still be possible to run into the same problem, as
we might need to allocate a page for the lwp's stack, and uvm_pagealloc
would kick the pagedaemon when memory was low.
	The new lwp we get from the cache isn't guaranteed to have an already
allocated stack page(s), is it?