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Date:      Wed, 19 Mar 2014 01:13:42 +0000 (UTC)
From:      Attilio Rao <attilio@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r263328 - in head/sys: dev/md vm
Message-ID:  <201403190113.s2J1Dgla051458@svn.freebsd.org>
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Author: attilio
Date: Wed Mar 19 01:13:42 2014
New Revision: 263328
URL: http://svnweb.freebsd.org/changeset/base/263328

Log:
  vm_page_grab() and vm_pager_get_pages() can drop the vm_object lock,
  then threads can sleep on the pip condition.
  Avoid to deadlock such threads by correctly awakening the sleeping ones
  after the pip is finished.
  swapoff side of the bug can likely result in shutdown deadlocks.
  
  Sponsored by:	EMC / Isilon Storage Division
  Reported by:	pho, pluknet
  Tested by:	pho

Modified:
  head/sys/dev/md/md.c
  head/sys/vm/swap_pager.c

Modified: head/sys/dev/md/md.c
==============================================================================
--- head/sys/dev/md/md.c	Wed Mar 19 00:55:12 2014	(r263327)
+++ head/sys/dev/md/md.c	Wed Mar 19 01:13:42 2014	(r263328)
@@ -903,7 +903,7 @@ mdstart_swap(struct md_s *sc, struct bio
 		offs = 0;
 		ma_offs += len;
 	}
-	vm_object_pip_subtract(sc->object, 1);
+	vm_object_pip_wakeup(sc->object);
 	VM_OBJECT_WUNLOCK(sc->object);
 	return (rv != VM_PAGER_ERROR ? 0 : ENOSPC);
 }

Modified: head/sys/vm/swap_pager.c
==============================================================================
--- head/sys/vm/swap_pager.c	Wed Mar 19 00:55:12 2014	(r263327)
+++ head/sys/vm/swap_pager.c	Wed Mar 19 01:13:42 2014	(r263328)
@@ -1713,7 +1713,7 @@ swp_pager_force_pagein(vm_object_t objec
 	vm_object_pip_add(object, 1);
 	m = vm_page_grab(object, pindex, VM_ALLOC_NORMAL);
 	if (m->valid == VM_PAGE_BITS_ALL) {
-		vm_object_pip_subtract(object, 1);
+		vm_object_pip_wakeup(object);
 		vm_page_dirty(m);
 		vm_page_lock(m);
 		vm_page_activate(m);
@@ -1725,7 +1725,7 @@ swp_pager_force_pagein(vm_object_t objec
 
 	if (swap_pager_getpages(object, &m, 1, 0) != VM_PAGER_OK)
 		panic("swap_pager_force_pagein: read from swap failed");/*XXX*/
-	vm_object_pip_subtract(object, 1);
+	vm_object_pip_wakeup(object);
 	vm_page_dirty(m);
 	vm_page_lock(m);
 	vm_page_deactivate(m);

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