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kernfs: replace kernfs_node->u.completion with kernfs_root->deactivate_waitq
kernfs_node->u.completion is used to notify deactivation completion from kernfs_put_active() to kernfs_deactivate(). We now allow multiple racing removals of the same node and the current removal scheme is no longer correct - kernfs_remove() invocation may return before the node is properly deactivated if it races against another removal. The removal path will be restructured to address the issue. To help such restructure which requires supporting multiple waiters, this patch replaces kernfs_node->u.completion with kernfs_root->deactivate_waitq. This makes deactivation event notifications share a per-root waitqueue_head; however, the wait path is quite cold and this will also allow shaving one pointer off kernfs_node. v2: Refreshed on top of ("kernfs: make kernfs_deactivate() honor KERNFS_LOCKDEP flag"). Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -8,6 +8,7 @@
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* This file is released under the GPLv2.
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*/
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#include <linux/sched.h>
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#include <linux/fs.h>
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#include <linux/namei.h>
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#include <linux/idr.h>
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@ -151,6 +152,7 @@ struct kernfs_node *kernfs_get_active(struct kernfs_node *kn)
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*/
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void kernfs_put_active(struct kernfs_node *kn)
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{
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struct kernfs_root *root = kernfs_root(kn);
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int v;
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if (unlikely(!kn))
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@ -162,11 +164,7 @@ void kernfs_put_active(struct kernfs_node *kn)
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if (likely(v != KN_DEACTIVATED_BIAS))
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return;
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/*
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* atomic_dec_return() is a mb(), we'll always see the updated
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* kn->u.completion.
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*/
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complete(kn->u.completion);
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wake_up_all(&root->deactivate_waitq);
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}
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/**
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@ -177,28 +175,24 @@ void kernfs_put_active(struct kernfs_node *kn)
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*/
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static void kernfs_deactivate(struct kernfs_node *kn)
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{
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DECLARE_COMPLETION_ONSTACK(wait);
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int v;
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struct kernfs_root *root = kernfs_root(kn);
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BUG_ON(!(kn->flags & KERNFS_REMOVED));
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if (!(kernfs_type(kn) & KERNFS_ACTIVE_REF))
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return;
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kn->u.completion = (void *)&wait;
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if (kn->flags & KERNFS_LOCKDEP)
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rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
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/* atomic_add_return() is a mb(), put_active() will always see
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* the updated kn->u.completion.
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*/
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v = atomic_add_return(KN_DEACTIVATED_BIAS, &kn->active);
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if (v != KN_DEACTIVATED_BIAS) {
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if (kn->flags & KERNFS_LOCKDEP)
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lock_contended(&kn->dep_map, _RET_IP_);
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wait_for_completion(&wait);
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}
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atomic_add(KN_DEACTIVATED_BIAS, &kn->active);
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if ((kn->flags & KERNFS_LOCKDEP) &&
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atomic_read(&kn->active) != KN_DEACTIVATED_BIAS)
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lock_contended(&kn->dep_map, _RET_IP_);
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wait_event(root->deactivate_waitq,
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atomic_read(&kn->active) == KN_DEACTIVATED_BIAS);
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if (kn->flags & KERNFS_LOCKDEP) {
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lock_acquired(&kn->dep_map, _RET_IP_);
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@ -630,6 +624,7 @@ struct kernfs_root *kernfs_create_root(struct kernfs_dir_ops *kdops, void *priv)
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root->dir_ops = kdops;
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root->kn = kn;
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init_waitqueue_head(&root->deactivate_waitq);
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return root;
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}
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@ -15,7 +15,7 @@
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#include <linux/lockdep.h>
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#include <linux/rbtree.h>
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#include <linux/atomic.h>
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#include <linux/completion.h>
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#include <linux/wait.h>
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struct file;
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struct dentry;
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@ -92,7 +92,6 @@ struct kernfs_node {
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struct rb_node rb;
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union {
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struct completion *completion;
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struct kernfs_node *removed_list;
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} u;
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@ -133,6 +132,7 @@ struct kernfs_root {
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/* private fields, do not use outside kernfs proper */
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struct ida ino_ida;
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struct kernfs_dir_ops *dir_ops;
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wait_queue_head_t deactivate_waitq;
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};
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struct kernfs_open_file {
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