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From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 7 Mar 2012 21:00:34 +0100
Subject: [PATCH 187/353] fs: dcache: Use cpu_chill() in trylock loops
Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=3b314979856ee6c2c76f4960791e7f42fe12a3df
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/autofs/expire.c | 3 ++-
fs/namespace.c | 8 ++++++--
2 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/fs/autofs/expire.c b/fs/autofs/expire.c
index 70e9afe589fb..1a6b88ad4fe0 100644
--- a/fs/autofs/expire.c
+++ b/fs/autofs/expire.c
@@ -8,6 +8,7 @@
* option, any later version, incorporated herein by reference.
*/
+#include <linux/delay.h>
#include "autofs_i.h"
/* Check if a dentry can be expired */
@@ -153,7 +154,7 @@ static struct dentry *get_next_positive_dentry(struct dentry *prev,
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);
diff --git a/fs/namespace.c b/fs/namespace.c
index 396ff1bcfdad..2c0ff275e978 100644
--- 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>
@@ -327,8 +328,11 @@ int __mnt_want_write(struct vfsmount *m)
* incremented count after it has set MNT_WRITE_HOLD.
*/
smp_mb();
- while (READ_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD)
- cpu_relax();
+ while (READ_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD) {
+ preempt_enable();
+ cpu_chill();
+ preempt_disable();
+ }
/*
* After the slowpath clears MNT_WRITE_HOLD, mnt_is_readonly will
* be set to match its requirements. So we must not load that until
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