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authorLinus Torvalds <torvalds@linux-foundation.org>2013-09-07 15:49:18 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-09-07 15:49:18 -0700
commite7d33bb5ea82922e6ddcfc6b28a630b1a4ced071 (patch)
tree6a3d2da32c73b38246750cd8d163029d8a9afcf3
parent44a0cf92926c343366a4986808d12ab068504eed (diff)
downloadlinux-e7d33bb5ea82922e6ddcfc6b28a630b1a4ced071.tar.gz
lockref: add ability to mark lockrefs "dead"
The only actual current lockref user (dcache) uses zero reference counts even for perfectly live dentries, because it's a cache: there may not be any users, but that doesn't mean that we want to throw away the dentry. At the same time, the dentry cache does have a notion of a truly "dead" dentry that we must not even increment the reference count of, because we have pruned it and it is not valid. Currently that distinction is not visible in the lockref itself, and the dentry cache validation uses "lockref_get_or_lock()" to either get a new reference to a dentry that already had existing references (and thus cannot be dead), or get the dentry lock so that we can then verify the dentry and increment the reference count under the lock if that verification was successful. That's all somewhat complicated. This adds the concept of being "dead" to the lockref itself, by simply using a count that is negative. This allows a usage scenario where we can increment the refcount of a dentry without having to validate it, and pushing the special "we killed it" case into the lockref code. The dentry code itself doesn't actually use this yet, and it's probably too late in the merge window to do that code (the dentry_kill() code with its "should I decrement the count" logic really is pretty complex code), but let's introduce the concept at the lockref level now. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/lockref.h3
-rw-r--r--lib/lockref.c38
2 files changed, 41 insertions, 0 deletions
diff --git a/include/linux/lockref.h b/include/linux/lockref.h
index ca07b5028b0..f279ed9a916 100644
--- a/include/linux/lockref.h
+++ b/include/linux/lockref.h
@@ -33,4 +33,7 @@ extern int lockref_get_not_zero(struct lockref *);
extern int lockref_get_or_lock(struct lockref *);
extern int lockref_put_or_lock(struct lockref *);
+extern void lockref_mark_dead(struct lockref *);
+extern int lockref_get_not_dead(struct lockref *);
+
#endif /* __LINUX_LOCKREF_H */
diff --git a/lib/lockref.c b/lib/lockref.c
index 7aae8df37f6..e2cd2c0a882 100644
--- a/lib/lockref.c
+++ b/lib/lockref.c
@@ -126,3 +126,41 @@ int lockref_put_or_lock(struct lockref *lockref)
return 1;
}
EXPORT_SYMBOL(lockref_put_or_lock);
+
+/**
+ * lockref_mark_dead - mark lockref dead
+ * @lockref: pointer to lockref structure
+ */
+void lockref_mark_dead(struct lockref *lockref)
+{
+ assert_spin_locked(&lockref->lock);
+ lockref->count = -128;
+}
+
+/**
+ * lockref_get_not_dead - Increments count unless the ref is dead
+ * @lockref: pointer to lockref structure
+ * Return: 1 if count updated successfully or 0 if lockref was dead
+ */
+int lockref_get_not_dead(struct lockref *lockref)
+{
+ int retval;
+
+ CMPXCHG_LOOP(
+ new.count++;
+ if ((int)old.count < 0)
+ return 0;
+ ,
+ return 1;
+ );
+
+ spin_lock(&lockref->lock);
+ retval = 0;
+ if ((int) lockref->count >= 0) {
+ lockref->count++;
+ retval = 1;
+ }
+ spin_unlock(&lockref->lock);
+ return retval;
+}
+EXPORT_SYMBOL(lockref_get_not_dead);