From: Antonio Huete Jimenez <tuxillo@quantumachine.net>
Date: Mon, 17 Oct 2011 19:26:22 +0000 (-0700)
Subject: pmap - Missing critical section when calling lwkt_ipiq_process().
X-Git-Url: https://gitweb.dragonflybsd.org/dragonfly.git/commitdiff_plain/db39668bd529972dc154be070b57f398dfe94449

pmap - Missing critical section when calling lwkt_ipiq_process().

- pmap_interlock_wait() explicitly calls lwkt_process_ipiq() which expects to
be in a critical section. We still need cpu_ccfence() to guarantee that
pmap->pm_active is always read inside the loop.

- Sync pmap_interlock_wait's comment for both i386 and x86_64.

DragonFly-bug: <http://bugs.dragonflybsd.org/issue2152>

Reviewed by: @dillon, @vsrinivas
---

diff --git a/sys/platform/pc32/i386/pmap.c b/sys/platform/pc32/i386/pmap.c
index 3bb09b8438..f7c79218ec 100644
--- a/sys/platform/pc32/i386/pmap.c
+++ b/sys/platform/pc32/i386/pmap.c
@@ -3489,11 +3489,12 @@ pmap_interlock_wait(struct vmspace *vm)
 
 	if (pmap->pm_active & CPUMASK_LOCK) {
 		DEBUG_PUSH_INFO("pmap_interlock_wait");
+		crit_enter();
 		while (pmap->pm_active & CPUMASK_LOCK) {
-			cpu_pause();
 			cpu_ccfence();
 			lwkt_process_ipiq();
 		}
+		crit_exit();
 		DEBUG_POP_INFO();
 	}
 }
diff --git a/sys/platform/pc64/x86_64/pmap.c b/sys/platform/pc64/x86_64/pmap.c
index 1f2a59f9d4..ac06c70459 100644
--- a/sys/platform/pc64/x86_64/pmap.c
+++ b/sys/platform/pc64/x86_64/pmap.c
@@ -3876,7 +3876,13 @@ pmap_setlwpvm(struct lwp *lp, struct vmspace *newvm)
 #ifdef SMP
 
 /*
- * Called when switching to a locked pmap
+ * Called when switching to a locked pmap, used to interlock against pmaps
+ * undergoing modifications to prevent us from activating the MMU for the
+ * target pmap until all such modifications have completed.  We have to do
+ * this because the thread making the modifications has already set up its
+ * SMP synchronization mask.
+ *
+ * No requirements.
  */
 void
 pmap_interlock_wait(struct vmspace *vm)
@@ -3885,11 +3891,12 @@ pmap_interlock_wait(struct vmspace *vm)
 
 	if (pmap->pm_active & CPUMASK_LOCK) {
 		DEBUG_PUSH_INFO("pmap_interlock_wait");
+		crit_enter();
 		while (pmap->pm_active & CPUMASK_LOCK) {
-			cpu_pause();
 			cpu_ccfence();
 			lwkt_process_ipiq();
 		}
+		crit_exit();
 		DEBUG_POP_INFO();
 	}
 }