Subject: fs: dcache: Use cpu_chill() in trylock loops
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 07 Mar 2012 21:00:34 +0100

Retry loops on RT might loop forever when the modifying side was
preempted. Use cpu_chill() instead of cpu_relax() to let the system
make progress.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
---
 fs/autofs4/autofs_i.h |    1 +
 fs/autofs4/expire.c   |    2 +-
 fs/dcache.c           |    7 ++++---
 fs/namespace.c        |    3 ++-
 4 files changed, 8 insertions(+), 5 deletions(-)

Index: linux-stable/fs/autofs4/autofs_i.h
===================================================================
--- linux-stable.orig/fs/autofs4/autofs_i.h
+++ linux-stable/fs/autofs4/autofs_i.h
@@ -34,6 +34,7 @@
 #include <linux/sched.h>
 #include <linux/mount.h>
 #include <linux/namei.h>
+#include <linux/delay.h>
 #include <asm/current.h>
 #include <asm/uaccess.h>
 
Index: linux-stable/fs/autofs4/expire.c
===================================================================
--- linux-stable.orig/fs/autofs4/expire.c
+++ linux-stable/fs/autofs4/expire.c
@@ -166,7 +166,7 @@ again:
 			parent = p->d_parent;
 			if (!spin_trylock(&parent->d_lock)) {
 				spin_unlock(&p->d_lock);
-				cpu_relax();
+				cpu_chill();
 				goto relock;
 			}
 			spin_unlock(&p->d_lock);
Index: linux-stable/fs/dcache.c
===================================================================
--- linux-stable.orig/fs/dcache.c
+++ linux-stable/fs/dcache.c
@@ -37,6 +37,7 @@
 #include <linux/rculist_bl.h>
 #include <linux/prefetch.h>
 #include <linux/ratelimit.h>
+#include <linux/delay.h>
 #include "internal.h"
 #include "mount.h"
 
@@ -488,7 +489,7 @@ static inline struct dentry *dentry_kill
 	if (inode && !spin_trylock(&inode->i_lock)) {
 relock:
 		spin_unlock(&dentry->d_lock);
-		cpu_relax();
+		cpu_chill();
 		return dentry; /* try again with same dentry */
 	}
 	if (IS_ROOT(dentry))
@@ -876,7 +877,7 @@ relock:
 
 		if (!spin_trylock(&dentry->d_lock)) {
 			spin_unlock(&dcache_lru_lock);
-			cpu_relax();
+			cpu_chill();
 			goto relock;
 		}
 
@@ -2115,7 +2116,7 @@ again:
 	if (dentry->d_count == 1) {
 		if (inode && !spin_trylock(&inode->i_lock)) {
 			spin_unlock(&dentry->d_lock);
-			cpu_relax();
+			cpu_chill();
 			goto again;
 		}
 		dentry->d_flags &= ~DCACHE_CANT_MOUNT;
Index: linux-stable/fs/namespace.c
===================================================================
--- linux-stable.orig/fs/namespace.c
+++ linux-stable/fs/namespace.c
@@ -20,6 +20,7 @@
 #include <linux/fs_struct.h>	/* get_fs_root et.al. */
 #include <linux/fsnotify.h>	/* fsnotify_vfsmount_delete */
 #include <linux/uaccess.h>
+#include <linux/delay.h>
 #include "pnode.h"
 #include "internal.h"
 
@@ -313,7 +314,7 @@ int __mnt_want_write(struct vfsmount *m)
 	smp_mb();
 	while (mnt->mnt.mnt_flags & MNT_WRITE_HOLD) {
 		preempt_enable();
-		cpu_relax();
+		cpu_chill();
 		preempt_disable();
 	}
 	/*