linux-kernel - Re: [patch 1/3] mmu

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Message-ID: <20080201023113.GB26420@sgi.com>
Date:	Thu, 31 Jan 2008 20:31:13 -0600
From:	Robin Holt <holt@....com>
To:	Christoph Lameter <clameter@....com>
Cc:	Andrea Arcangeli <andrea@...ranet.com>, Robin Holt <holt@....com>,
	Avi Kivity <avi@...ranet.com>, Izik Eidus <izike@...ranet.com>,
	kvm-devel@...ts.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com
Subject: Re: [patch 1/3] mmu_notifier: Core code

Christoph,

Jack has repeatedly pointed out needing an unregister outside the
mmap_sem.  I still don't see the benefit to not having the lock in the mm.

Thanks,
Robin

Index: mmu_notifiers-cl-v4/include/linux/mm_types.h
===================================================================
--- mmu_notifiers-cl-v4.orig/include/linux/mm_types.h	2008-01-31 19:56:08.000000000 -0600
+++ mmu_notifiers-cl-v4/include/linux/mm_types.h	2008-01-31 19:56:58.000000000 -0600
@@ -155,6 +155,7 @@ struct vm_area_struct {
 
 struct mmu_notifier_head {
 #ifdef CONFIG_MMU_NOTIFIER
+	spinlock_t	list_lock;
 	struct hlist_head head;
 #endif
 };
Index: mmu_notifiers-cl-v4/mm/mmu_notifier.c
===================================================================
--- mmu_notifiers-cl-v4.orig/mm/mmu_notifier.c	2008-01-31 19:56:08.000000000 -0600
+++ mmu_notifiers-cl-v4/mm/mmu_notifier.c	2008-01-31 20:26:31.000000000 -0600
@@ -60,25 +60,19 @@ int mmu_notifier_age_page(struct mm_stru
  * Note that all notifiers use RCU. The updates are only guaranteed to be
  * visible to other processes after a RCU quiescent period!
  */
-void __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
-{
-	hlist_add_head_rcu(&mn->hlist, &mm->mmu_notifier.head);
-}
-EXPORT_SYMBOL_GPL(__mmu_notifier_register);
-
 void mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 {
-	down_write(&mm->mmap_sem);
-	__mmu_notifier_register(mn, mm);
-	up_write(&mm->mmap_sem);
+	spin_lock(&mm->mmu_notifier.list_lock);
+	hlist_add_head_rcu(&mn->hlist, &mm->mmu_notifier.head);
+	spin_unlock(&mm->mmu_notifier.list_lock);
 }
 EXPORT_SYMBOL_GPL(mmu_notifier_register);
 
 void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
 {
-	down_write(&mm->mmap_sem);
+	spin_lock(&mm->mmu_notifier.list_lock);
 	hlist_del_rcu(&mn->hlist);
-	up_write(&mm->mmap_sem);
+	spin_unlock(&mm->mmu_notifier.list_lock);
 }
 EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
 
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