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Date:      Tue, 24 Sep 2013 12:26:44 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r255845 - head/sys/amd64/amd64
Message-ID:  <201309241226.r8OCQitH063795@svn.freebsd.org>
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Author: kib
Date: Tue Sep 24 12:26:43 2013
New Revision: 255845
URL: http://svnweb.freebsd.org/changeset/base/255845

Log:
  Use the pv lists generation count to read-lock the pvh_global_lock in
  pmap_clear_modify().
  
  Noted and reviewed by:	alc
  Tested by:	pho
  Sponsored by:	The FreeBSD Foundation
  Approved by:	re (marius)

Modified:
  head/sys/amd64/amd64/pmap.c

Modified: head/sys/amd64/amd64/pmap.c
==============================================================================
--- head/sys/amd64/amd64/pmap.c	Tue Sep 24 12:24:48 2013	(r255844)
+++ head/sys/amd64/amd64/pmap.c	Tue Sep 24 12:26:43 2013	(r255845)
@@ -5314,7 +5314,9 @@ pmap_clear_modify(vm_page_t m)
 	pv_entry_t next_pv, pv;
 	pd_entry_t oldpde, *pde;
 	pt_entry_t oldpte, *pte;
+	struct rwlock *lock;
 	vm_offset_t va;
+	int md_gen, pvh_gen;
 
 	KASSERT((m->oflags & VPO_UNMANAGED) == 0,
 	    ("pmap_clear_modify: page %p is not managed", m));
@@ -5329,18 +5331,30 @@ pmap_clear_modify(vm_page_t m)
 	 */
 	if ((m->aflags & PGA_WRITEABLE) == 0)
 		return;
-	rw_wlock(&pvh_global_lock);
+	rw_rlock(&pvh_global_lock);
+	lock = VM_PAGE_TO_PV_LIST_LOCK(m);
+	rw_wlock(lock);
+restart:
 	if ((m->flags & PG_FICTITIOUS) != 0)
 		goto small_mappings;
 	pvh = pa_to_pvh(VM_PAGE_TO_PHYS(m));
 	TAILQ_FOREACH_SAFE(pv, &pvh->pv_list, pv_next, next_pv) {
 		pmap = PV_PMAP(pv);
-		PMAP_LOCK(pmap);
+		if (!PMAP_TRYLOCK(pmap)) {
+			pvh_gen = pvh->pv_gen;
+			rw_wunlock(lock);
+			PMAP_LOCK(pmap);
+			rw_wlock(lock);
+			if (pvh_gen != pvh->pv_gen) {
+				PMAP_UNLOCK(pmap);
+				goto restart;
+			}
+		}
 		va = pv->pv_va;
 		pde = pmap_pde(pmap, va);
 		oldpde = *pde;
 		if ((oldpde & PG_RW) != 0) {
-			if (pmap_demote_pde(pmap, pde, va)) {
+			if (pmap_demote_pde_locked(pmap, pde, va, &lock)) {
 				if ((oldpde & PG_W) == 0) {
 					/*
 					 * Write protect the mapping to a
@@ -5367,7 +5381,17 @@ pmap_clear_modify(vm_page_t m)
 small_mappings:
 	TAILQ_FOREACH(pv, &m->md.pv_list, pv_next) {
 		pmap = PV_PMAP(pv);
-		PMAP_LOCK(pmap);
+		if (!PMAP_TRYLOCK(pmap)) {
+			md_gen = m->md.pv_gen;
+			pvh_gen = pvh->pv_gen;
+			rw_wunlock(lock);
+			PMAP_LOCK(pmap);
+			rw_wlock(lock);
+			if (pvh_gen != pvh->pv_gen || md_gen != m->md.pv_gen) {
+				PMAP_UNLOCK(pmap);
+				goto restart;
+			}
+		}
 		pde = pmap_pde(pmap, pv->pv_va);
 		KASSERT((*pde & PG_PS) == 0, ("pmap_clear_modify: found"
 		    " a 2mpage in page %p's pv list", m));
@@ -5378,7 +5402,8 @@ small_mappings:
 		}
 		PMAP_UNLOCK(pmap);
 	}
-	rw_wunlock(&pvh_global_lock);
+	rw_wunlock(lock);
+	rw_runlock(&pvh_global_lock);
 }
 
 /*

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