Alan Cox d936694f09 Consider three objects, O, BO, and BBO, where BO is O's backing object ... and BBO is BO's backing object. Now, suppose that O and BO are being collapsed. Furthermore, suppose that BO has been marked dead (OBJ_DEAD) by vm_object_backing_scan() and that either vm_object_backing_scan() has been forced to sleep due to encountering a busy page or vm_object_collapse() has been forced to sleep due to memory allocation in the swap pager. If vm_object_deallocate() is then called on BBO and BO is BBO's only shadow object, vm_object_deallocate() will collapse BO and BBO. In doing so, it adds a necessary temporary reference to BO. If this collapse also sleeps and the prior collapse resumes first, the temporary reference will cause vm_object_collapse to panic with the message "backing_object %p was somehow re-referenced during collapse!" Resolve this race by changing vm_object_deallocate() such that it doesn't collapse BO and BBO if BO is marked dead. Once O and BO are collapsed, vm_object_collapse() will attempt to collapse O and BBO. So, vm_object_deallocate() on BBO need do nothing. Reported by: Peter Holm on 20050107 URL: http://www.holm.cc/stress/log/cons102.html In collaboration with: tegge@ Candidate for RELENG_4 and RELENG_5 MFC after: 2 weeks		2005-01-15 21:12:47 +00:00
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default_pager.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
device_pager.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
phys_pager.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
pmap.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
swap_pager.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
swap_pager.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
uma_core.c	While we want the recursion protection for the bucket zones so that	2005-01-11 03:33:09 +00:00
uma_dbg.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
uma_dbg.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
uma_int.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
uma.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_contig.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_extern.h	Disable U area swapping and remove the routines that create, destroy,	2004-11-20 02:29:00 +00:00
vm_fault.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_glue.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_init.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_kern.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_kern.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_map.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_map.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_meter.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_mmap.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_object.c	Consider three objects, O, BO, and BBO, where BO is O's backing object	2005-01-15 21:12:47 +00:00
vm_object.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_page.c	Transfer responsibility for freeing the page taken from the cache	2005-01-07 05:02:19 +00:00
vm_page.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_pageout.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_pageout.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_pageq.c	Remove references to L1 in the comments, according to Alan they are	2004-06-07 19:33:05 +00:00
vm_pager.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_pager.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_param.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_unix.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vm_zeroidle.c	Remove dangling variable	2004-11-06 11:33:11 +00:00
vm.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vnode_pager.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
vnode_pager.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00