Subject: fs: dcache: Use cpu_chill() in trylock loops
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 07 Mar 2012 21:00:34 +0100
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.8/older/patches-4.8.14-rt9.tar.xz

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/dcache.c           |   20 ++++++++++++++++----
 fs/namespace.c        |    3 ++-
 4 files changed, 20 insertions(+), 6 deletions(-)

--- a/fs/autofs4/autofs_i.h
+++ b/fs/autofs4/autofs_i.h
@@ -30,6 +30,7 @@
 #include <linux/sched.h>
 #include <linux/mount.h>
 #include <linux/namei.h>
+#include <linux/delay.h>
 #include <asm/current.h>
 #include <linux/uaccess.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/dcache.c
+++ b/fs/dcache.c
@@ -19,6 +19,7 @@
 #include <linux/mm.h>
 #include <linux/fs.h>
 #include <linux/fsnotify.h>
+#include <linux/delay.h>
 #include <linux/slab.h>
 #include <linux/init.h>
 #include <linux/hash.h>
@@ -750,6 +751,8 @@ static inline bool fast_dput(struct dent
  */
 void dput(struct dentry *dentry)
 {
+	struct dentry *parent;
+
 	if (unlikely(!dentry))
 		return;
 
@@ -788,9 +791,18 @@ void dput(struct dentry *dentry)
 	return;
 
 kill_it:
-	dentry = dentry_kill(dentry);
-	if (dentry) {
-		cond_resched();
+	parent = dentry_kill(dentry);
+	if (parent) {
+		int r;
+
+		if (parent == dentry) {
+			/* the task with the highest priority won't schedule */
+			r = cond_resched();
+			if (!r)
+				cpu_chill();
+		} else {
+			dentry = parent;
+		}
 		goto repeat;
 	}
 }
@@ -2321,7 +2333,7 @@ void d_delete(struct dentry * dentry)
 	if (dentry->d_lockref.count == 1) {
 		if (!spin_trylock(&inode->i_lock)) {
 			spin_unlock(&dentry->d_lock);
-			cpu_relax();
+			cpu_chill();
 			goto again;
 		}
 		dentry->d_flags &= ~DCACHE_CANT_MOUNT;
--- 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/idr.h>
 #include <linux/init.h>		/* init_rootfs */
@@ -355,7 +356,7 @@ int __mnt_want_write(struct vfsmount *m)
 	smp_mb();
 	while (ACCESS_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD) {
 		preempt_enable();
-		cpu_relax();
+		cpu_chill();
 		preempt_disable();
 	}
 	/*