patches/fs-dcache-use-cpu-chill-in-trylock-loops.patch

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>

---
 fs/autofs4/autofs_i.h |    1 +
 fs/autofs4/expire.c   |    2 +-
 fs/namespace.c        |    3 ++-
 3 files changed, 4 insertions(+), 2 deletions(-)

--- a/fs/autofs4/autofs_i.h
+++ b/fs/autofs4/autofs_i.h
@@ -20,6 +20,7 @@
 #include <linux/sched.h>
 #include <linux/mount.h>
 #include <linux/namei.h>
+#include <linux/delay.h>
 #include <linux/uaccess.h>
 #include <linux/mutex.h>
 #include <linux/spinlock.h>
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -148,7 +148,7 @@ static struct dentry *get_next_positive_
 			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);
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -14,6 +14,7 @@
 #include <linux/mnt_namespace.h>
 #include <linux/user_namespace.h>
 #include <linux/namei.h>
+#include <linux/delay.h>
 #include <linux/security.h>
 #include <linux/cred.h>
 #include <linux/idr.h>
@@ -355,7 +356,7 @@ int __mnt_want_write(struct vfsmount *m)
 	smp_mb();
 	while (READ_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD) {
 		preempt_enable();
-		cpu_relax();
+		cpu_chill();
 		preempt_disable();
 	}
 	/*