diff options
Diffstat (limited to 'fs/dcache.c')
| -rw-r--r-- | fs/dcache.c | 149 |
1 files changed, 114 insertions, 35 deletions
diff --git a/fs/dcache.c b/fs/dcache.c index 7d34f04..dc400fd 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -511,7 +511,7 @@ static void __dentry_kill(struct dentry *dentry) * 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); @@ -564,7 +564,7 @@ static inline struct dentry *lock_parent(struct dentry *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; @@ -593,6 +593,110 @@ again: 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 * @@ -625,8 +729,14 @@ void dput(struct dentry *dentry) 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))) @@ -813,7 +923,7 @@ static void shrink_dentry_list(struct list_head *list) * 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); @@ -2191,37 +2301,6 @@ struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name) } 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 |
