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List:       openbsd-tech
Subject:    Re: Prevent off-by-one accounting hang in out-of-swap situations
From:       Martin Pieuchot <mpi () openbsd ! org>
Date:       2023-10-26 13:51:12
Message-ID: ZTpu0O-9ysIA-xc1 () oliva ! grenadille ! net
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On 26/10/23(Thu) 07:06, Miod Vallat wrote:
> > I wonder if the diff below makes a difference.  It's hard to debug and it
> > might be worth adding a counter for bad swap slots.
> 
> It did not help (but your diff is probably correct).

In that case I'd like to put both diffs in, are you ok with that?

> > Index: uvm/uvm_anon.c
> > ===================================================================
> > RCS file: /cvs/src/sys/uvm/uvm_anon.c,v
> > retrieving revision 1.56
> > diff -u -p -r1.56 uvm_anon.c
> > --- uvm/uvm_anon.c	2 Sep 2023 08:24:40 -0000	1.56
> > +++ uvm/uvm_anon.c	22 Oct 2023 21:27:42 -0000
> > @@ -116,7 +116,7 @@ uvm_anfree_list(struct vm_anon *anon, st
> >  			uvm_unlock_pageq();	/* free the daemon */
> >  		}
> >  	} else {
> > -		if (anon->an_swslot != 0) {
> > +		if (anon->an_swslot != 0 && anon->an_swslot != SWSLOT_BAD) {
> >  			/* This page is no longer only in swap. */
> >  			KASSERT(uvmexp.swpgonly > 0);
> >  			atomic_dec_int(&uvmexp.swpgonly);

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