checked nix/port/page.c. your duppage() is wrong.
/* don't dup pages with no image */
if(p->ref == 0 || p->image == nil || p->image->notext)
return 0;
/*
* normal lock ordering is to call
* lock(&pga) before lock(p).
* To avoid deadlock, we have to drop
* our locks and try again.
*/
if(!canlock(&pga)){
unlock(p);
if(up)
sched();
lock(p);
goto retry;
}
you need to check p->ref != 1 instead of p->ref == 0. the page
passed to duppage() is still cached. after you unlock(p), someone
can come in and take a reference to the page from the image
cache (lookpage()), making p->ref > 1 once you get the lock back.
put an assert or print in there after the if(!canlock(&pga){} block
to check p->ref.
when this happens, the caller to duppage() (fixfault) must not
modify the page or use it in his procs segment (on copy on write)
but make a copy for itself because the other processes that
grabbed the reference is (commited to) reading it (outside of the
page lock of course, so you already lost when p->ref != 1).
--
cinap
