mirror of https://gitee.com/openkylin/linux.git
get rid of trylock loop in locking dentries on shrink list
In case of trylock failure don't re-add to the list - drop the locks and carefully get them in the right order. For shrink_dentry_list(), somebody having grabbed a reference to dentry means that we can kick it off-list, so if we find dentry being modified under us we don't need to play silly buggers with retries anyway - off the list it is. The locking logics taken out into a helper of its own; lock_parent() is no longer used for dentries that can be killed under us. [fix from Eric Biggers folded] Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
parent
c19457f0ae
commit
3b3f09f48b
106
fs/dcache.c
106
fs/dcache.c
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@ -974,56 +974,86 @@ void d_prune_aliases(struct inode *inode)
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}
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}
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EXPORT_SYMBOL(d_prune_aliases);
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EXPORT_SYMBOL(d_prune_aliases);
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/*
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* Lock a dentry from shrink list.
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* Note that dentry is *not* protected from concurrent dentry_kill(),
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* d_delete(), etc. It is protected from freeing (by the fact of
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* being on a shrink list), but everything else is fair game.
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* Return false if dentry has been disrupted or grabbed, leaving
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* the caller to kick it off-list. Otherwise, return true and have
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* that dentry's inode and parent both locked.
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*/
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static bool shrink_lock_dentry(struct dentry *dentry)
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{
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struct inode *inode;
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struct dentry *parent;
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if (dentry->d_lockref.count)
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return false;
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inode = dentry->d_inode;
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if (inode && unlikely(!spin_trylock(&inode->i_lock))) {
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rcu_read_lock(); /* to protect inode */
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spin_unlock(&dentry->d_lock);
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spin_lock(&inode->i_lock);
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spin_lock(&dentry->d_lock);
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if (unlikely(dentry->d_lockref.count))
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goto out;
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/* changed inode means that somebody had grabbed it */
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if (unlikely(inode != dentry->d_inode))
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goto out;
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rcu_read_unlock();
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}
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parent = dentry->d_parent;
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if (IS_ROOT(dentry) || likely(spin_trylock(&parent->d_lock)))
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return true;
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rcu_read_lock(); /* to protect parent */
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spin_unlock(&dentry->d_lock);
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parent = READ_ONCE(dentry->d_parent);
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spin_lock(&parent->d_lock);
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if (unlikely(parent != dentry->d_parent)) {
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spin_unlock(&parent->d_lock);
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spin_lock(&dentry->d_lock);
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goto out;
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}
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spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
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if (likely(!dentry->d_lockref.count)) {
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rcu_read_unlock();
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return true;
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}
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spin_unlock(&parent->d_lock);
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out:
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if (inode)
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spin_unlock(&inode->i_lock);
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rcu_read_unlock();
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return false;
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}
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static void shrink_dentry_list(struct list_head *list)
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static void shrink_dentry_list(struct list_head *list)
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{
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{
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struct dentry *dentry, *parent;
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while (!list_empty(list)) {
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while (!list_empty(list)) {
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struct dentry *dentry, *parent;
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struct inode *inode;
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struct inode *inode;
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dentry = list_entry(list->prev, struct dentry, d_lru);
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dentry = list_entry(list->prev, struct dentry, d_lru);
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spin_lock(&dentry->d_lock);
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spin_lock(&dentry->d_lock);
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parent = lock_parent(dentry);
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if (!shrink_lock_dentry(dentry)) {
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bool can_free = false;
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/*
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d_shrink_del(dentry);
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* The dispose list is isolated and dentries are not accounted
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if (dentry->d_lockref.count < 0)
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* to the LRU here, so we can simply remove it from the list
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can_free = dentry->d_flags & DCACHE_MAY_FREE;
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* here regardless of whether it is referenced or not.
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*/
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d_shrink_del(dentry);
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/*
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* We found an inuse dentry which was not removed from
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* the LRU because of laziness during lookup. Do not free it.
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*/
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if (dentry->d_lockref.count > 0) {
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spin_unlock(&dentry->d_lock);
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spin_unlock(&dentry->d_lock);
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if (parent)
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spin_unlock(&parent->d_lock);
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continue;
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}
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if (unlikely(dentry->d_flags & DCACHE_DENTRY_KILLED)) {
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bool can_free = dentry->d_flags & DCACHE_MAY_FREE;
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spin_unlock(&dentry->d_lock);
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if (parent)
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spin_unlock(&parent->d_lock);
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if (can_free)
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if (can_free)
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dentry_free(dentry);
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dentry_free(dentry);
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continue;
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continue;
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}
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}
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d_shrink_del(dentry);
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inode = dentry->d_inode;
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parent = dentry->d_parent;
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if (inode && unlikely(!spin_trylock(&inode->i_lock))) {
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d_shrink_add(dentry, list);
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spin_unlock(&dentry->d_lock);
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if (parent)
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spin_unlock(&parent->d_lock);
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continue;
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}
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__dentry_kill(dentry);
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__dentry_kill(dentry);
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if (parent == dentry)
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continue;
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/*
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/*
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* We need to prune ancestors too. This is necessary to prevent
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* We need to prune ancestors too. This is necessary to prevent
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* quadratic behavior of shrink_dcache_parent(), but is also
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* quadratic behavior of shrink_dcache_parent(), but is also
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