* dentry_iput drops the locks, at which point nobody (except
* transient RCU lookups) can reach this dentry.
*/
- BUG_ON((int)dentry->d_lockref.count > 0);
+ BUG_ON(dentry->d_lockref.count > 0);
this_cpu_dec(nr_dentry);
if (dentry->d_op && dentry->d_op->d_release)
dentry->d_op->d_release(dentry);
struct dentry *parent = dentry->d_parent;
if (IS_ROOT(dentry))
return NULL;
- if (unlikely((int)dentry->d_lockref.count < 0))
+ if (unlikely(dentry->d_lockref.count < 0))
return NULL;
if (likely(spin_trylock(&parent->d_lock)))
return parent;
return parent;
}
+/*
+ * Try to do a lockless dput(), and return whether that was successful.
+ *
+ * If unsuccessful, we return false, having already taken the dentry lock.
+ *
+ * The caller needs to hold the RCU read lock, so that the dentry is
+ * guaranteed to stay around even if the refcount goes down to zero!
+ */
+static inline bool fast_dput(struct dentry *dentry)
+{
+ int ret;
+ unsigned int d_flags;
+
+ /*
+ * If we have a d_op->d_delete() operation, we sould not
+ * let the dentry count go to zero, so use "put__or_lock".
+ */
+ if (unlikely(dentry->d_flags & DCACHE_OP_DELETE))
+ return lockref_put_or_lock(&dentry->d_lockref);
+
+ /*
+ * .. otherwise, we can try to just decrement the
+ * lockref optimistically.
+ */
+ ret = lockref_put_return(&dentry->d_lockref);
+
+ /*
+ * If the lockref_put_return() failed due to the lock being held
+ * by somebody else, the fast path has failed. We will need to
+ * get the lock, and then check the count again.
+ */
+ if (unlikely(ret < 0)) {
+ spin_lock(&dentry->d_lock);
+ if (dentry->d_lockref.count > 1) {
+ dentry->d_lockref.count--;
+ spin_unlock(&dentry->d_lock);
+ return 1;
+ }
+ return 0;
+ }
+
+ /*
+ * If we weren't the last ref, we're done.
+ */
+ if (ret)
+ return 1;
+
+ /*
+ * Careful, careful. The reference count went down
+ * to zero, but we don't hold the dentry lock, so
+ * somebody else could get it again, and do another
+ * dput(), and we need to not race with that.
+ *
+ * However, there is a very special and common case
+ * where we don't care, because there is nothing to
+ * do: the dentry is still hashed, it does not have
+ * a 'delete' op, and it's referenced and already on
+ * the LRU list.
+ *
+ * NOTE! Since we aren't locked, these values are
+ * not "stable". However, it is sufficient that at
+ * some point after we dropped the reference the
+ * dentry was hashed and the flags had the proper
+ * value. Other dentry users may have re-gotten
+ * a reference to the dentry and change that, but
+ * our work is done - we can leave the dentry
+ * around with a zero refcount.
+ */
+ smp_rmb();
+ d_flags = ACCESS_ONCE(dentry->d_flags);
+ d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST;
+
+ /* Nothing to do? Dropping the reference was all we needed? */
+ if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry))
+ return 1;
+
+ /*
+ * Not the fast normal case? Get the lock. We've already decremented
+ * the refcount, but we'll need to re-check the situation after
+ * getting the lock.
+ */
+ spin_lock(&dentry->d_lock);
+
+ /*
+ * Did somebody else grab a reference to it in the meantime, and
+ * we're no longer the last user after all? Alternatively, somebody
+ * else could have killed it and marked it dead. Either way, we
+ * don't need to do anything else.
+ */
+ if (dentry->d_lockref.count) {
+ spin_unlock(&dentry->d_lock);
+ return 1;
+ }
+
+ /*
+ * Re-get the reference we optimistically dropped. We hold the
+ * lock, and we just tested that it was zero, so we can just
+ * set it to 1.
+ */
+ dentry->d_lockref.count = 1;
+ return 0;
+}
+
+
/*
* This is dput
*
return;
repeat:
- if (lockref_put_or_lock(&dentry->d_lockref))
+ rcu_read_lock();
+ if (likely(fast_dput(dentry))) {
+ rcu_read_unlock();
return;
+ }
+
+ /* Slow case: now with the dentry lock held */
+ rcu_read_unlock();
/* Unreachable? Get rid of it */
if (unlikely(d_unhashed(dentry)))
* We found an inuse dentry which was not removed from
* the LRU because of laziness during lookup. Do not free it.
*/
- if ((int)dentry->d_lockref.count > 0) {
+ if (dentry->d_lockref.count > 0) {
spin_unlock(&dentry->d_lock);
if (parent)
spin_unlock(&parent->d_lock);
}
EXPORT_SYMBOL(d_hash_and_lookup);
-/**
- * d_validate - verify dentry provided from insecure source (deprecated)
- * @dentry: The dentry alleged to be valid child of @dparent
- * @dparent: The parent dentry (known to be valid)
- *
- * An insecure source has sent us a dentry, here we verify it and dget() it.
- * This is used by ncpfs in its readdir implementation.
- * Zero is returned in the dentry is invalid.
- *
- * This function is slow for big directories, and deprecated, do not use it.
- */
-int d_validate(struct dentry *dentry, struct dentry *dparent)
-{
- struct dentry *child;
-
- spin_lock(&dparent->d_lock);
- list_for_each_entry(child, &dparent->d_subdirs, d_child) {
- if (dentry == child) {
- spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
- __dget_dlock(dentry);
- spin_unlock(&dentry->d_lock);
- spin_unlock(&dparent->d_lock);
- return 1;
- }
- }
- spin_unlock(&dparent->d_lock);
-
- return 0;
-}
-EXPORT_SYMBOL(d_validate);
-
/*
* When a file is deleted, we have two options:
* - turn this dentry into a negative dentry
projects / linux-drm-fsl-dcu.git / blobdiff