Message-Id: <1351090849-31667-1-git-send-email-nzimmer@sgi.com>
Date:	Wed, 24 Oct 2012 10:00:49 -0500
From:	Nathan Zimmer <nzimmer@....com>
To:	unlisted-recipients:; (no To-header on input)
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Nathan Zimmer <nzimmer@....com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	David Woodhouse <dwmw2@...radead.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH v2] procfs: Improve Scaling in proc

I am currently tracking a hotlock reported by a customer on a large, 512 cores,
system, I am currently running 3.7.0 rc1 but the issue looks like it has been
this way for a very long time.
The offending lock is proc_dir_entry->pde_unload_lock.

This patch converts the replaces the lock with the rcu. It is a refresh of what
was orignally suggested by Eric Dumazet.  I refreshed it to the 3.7.

Supporting numbers, lower is better, they are from the test I posted earlier.
cpuinfo baseline        Rcu
tasks   read-sec        read-sec
1       0.0141          0.0141
2       0.0140          0.0142
4       0.0140          0.0141
8       0.0145          0.0140
16      0.0553          0.0168
32      0.1688          0.0549
64      0.5017          0.1690
128     1.7005          0.5038
256     5.2513          2.0804
512     8.0529          3.0162

V2 Use the completion mechanism instead of a polling loop.

Cc: Eric Dumazet <eric.dumazet@...il.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Alexey Dobriyan <adobriyan@...il.com>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Signed-off-by: Nathan Zimmer <nzimmer@....com>

---
 fs/proc/generic.c       |   56 +++++-----
 fs/proc/inode.c         |  252 +++++++++++++++++++++++++++++------------------
 fs/proc/internal.h      |    2 +
 include/linux/proc_fs.h |    6 +-
 4 files changed, 190 insertions(+), 126 deletions(-)

Index: linux/fs/proc/generic.c
===================================================================
--- linux.orig/fs/proc/generic.c	2012-10-24 09:01:07.291374770 -0500
+++ linux/fs/proc/generic.c	2012-10-24 09:13:36.473351092 -0500
@@ -22,6 +22,7 @@
 #include <linux/bitops.h>
 #include <linux/spinlock.h>
 #include <linux/completion.h>
+#include <linux/sched.h>
 #include <asm/uaccess.h>
 
 #include "internal.h"
@@ -190,14 +191,16 @@ proc_file_read(struct file *file, char _
 {
 	struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
 	ssize_t rv = -EIO;
+	const struct file_operations *fops;
 
-	spin_lock(&pde->pde_unload_lock);
-	if (!pde->proc_fops) {
-		spin_unlock(&pde->pde_unload_lock);
+	rcu_read_lock();
+	fops = rcu_dereference(pde->proc_fops);
+	if (!fops) {
+		rcu_read_unlock();
 		return rv;
 	}
-	pde->pde_users++;
-	spin_unlock(&pde->pde_unload_lock);
+	atomic_inc(&pde->pde_users);
+	rcu_read_unlock();
 
 	rv = __proc_file_read(file, buf, nbytes, ppos);
 
@@ -213,13 +216,16 @@ proc_file_write(struct file *file, const
 	ssize_t rv = -EIO;
 
 	if (pde->write_proc) {
-		spin_lock(&pde->pde_unload_lock);
-		if (!pde->proc_fops) {
-			spin_unlock(&pde->pde_unload_lock);
+		const struct file_operations *fops;
+
+		rcu_read_lock();
+		fops = rcu_dereference(pde->proc_fops);
+		if (!fops) {
+			rcu_read_unlock();
 			return rv;
 		}
-		pde->pde_users++;
-		spin_unlock(&pde->pde_unload_lock);
+		atomic_inc(&pde->pde_users);
+		rcu_read_unlock();
 
 		/* FIXME: does this routine need ppos?  probably... */
 		rv = pde->write_proc(file, buffer, count, pde->data);
@@ -564,7 +570,7 @@ static int proc_register(struct proc_dir
 
 	if (S_ISDIR(dp->mode)) {
 		if (dp->proc_iops == NULL) {
-			dp->proc_fops = &proc_dir_operations;
+			RCU_INIT_POINTER(dp->proc_fops, &proc_dir_operations);
 			dp->proc_iops = &proc_dir_inode_operations;
 		}
 		dir->nlink++;
@@ -573,7 +579,7 @@ static int proc_register(struct proc_dir
 			dp->proc_iops = &proc_link_inode_operations;
 	} else if (S_ISREG(dp->mode)) {
 		if (dp->proc_fops == NULL)
-			dp->proc_fops = &proc_file_operations;
+			RCU_INIT_POINTER(dp->proc_fops, &proc_file_operations);
 		if (dp->proc_iops == NULL)
 			dp->proc_iops = &proc_file_inode_operations;
 	}
@@ -626,8 +632,7 @@ static struct proc_dir_entry *__proc_cre
 	ent->mode = mode;
 	ent->nlink = nlink;
 	atomic_set(&ent->count, 1);
-	spin_lock_init(&ent->pde_unload_lock);
-	INIT_LIST_HEAD(&ent->pde_openers);
+	atomic_set(&ent->pde_users, 1);
 out:
 	return ent;
 }
@@ -750,7 +755,7 @@ struct proc_dir_entry *proc_create_data(
 	pde = __proc_create(&parent, name, mode, nlink);
 	if (!pde)
 		goto out;
-	pde->proc_fops = proc_fops;
+	rcu_assign_pointer(pde->proc_fops, proc_fops);
 	pde->data = data;
 	if (proc_register(parent, pde) < 0)
 		goto out_free;
@@ -786,6 +791,7 @@ void remove_proc_entry(const char *name,
 	struct proc_dir_entry *de = NULL;
 	const char *fn = name;
 	unsigned int len;
+	LIST_HEAD(purge_queue);
 
 	spin_lock(&proc_subdir_lock);
 	if (__xlate_proc_name(name, &parent, &fn) != 0) {
@@ -808,37 +814,31 @@ void remove_proc_entry(const char *name,
 		return;
 	}
 
-	spin_lock(&de->pde_unload_lock);
 	/*
 	 * Stop accepting new callers into module. If you're
 	 * dynamically allocating ->proc_fops, save a pointer somewhere.
 	 */
-	de->proc_fops = NULL;
-	/* Wait until all existing callers into module are done. */
-	if (de->pde_users > 0) {
-		DECLARE_COMPLETION_ONSTACK(c);
+	rcu_assign_pointer(de->proc_fops, NULL);
+	synchronize_rcu();
+	DECLARE_COMPLETION_ONSTACK(c);
+	if (!atomic_dec_and_test(&de->pde_users)) {
 
 		if (!de->pde_unload_completion)
 			de->pde_unload_completion = &c;
 
-		spin_unlock(&de->pde_unload_lock);
-
 		wait_for_completion(de->pde_unload_completion);
 
-		spin_lock(&de->pde_unload_lock);
 	}
+	pde_openers_purge(de, &purge_queue);
 
-	while (!list_empty(&de->pde_openers)) {
+	while (!list_empty(&purge_queue)) {
 		struct pde_opener *pdeo;
 
-		pdeo = list_first_entry(&de->pde_openers, struct pde_opener, lh);
+		pdeo = list_first_entry(&purge_queue, struct pde_opener, lh);
 		list_del(&pdeo->lh);
-		spin_unlock(&de->pde_unload_lock);
 		pdeo->release(pdeo->inode, pdeo->file);
 		kfree(pdeo);
-		spin_lock(&de->pde_unload_lock);
 	}
-	spin_unlock(&de->pde_unload_lock);
 
 	if (S_ISDIR(de->mode))
 		parent->nlink--;
Index: linux/fs/proc/inode.c
===================================================================
--- linux.orig/fs/proc/inode.c	2012-10-24 09:01:07.299374618 -0500
+++ linux/fs/proc/inode.c	2012-10-24 09:25:03.036343215 -0500
@@ -21,6 +21,7 @@
 #include <linux/seq_file.h>
 #include <linux/slab.h>
 #include <linux/mount.h>
+#include <linux/hash.h>
 
 #include <asm/uaccess.h>
 
@@ -94,8 +95,27 @@ static void init_once(void *foo)
 	inode_init_once(&ei->vfs_inode);
 }
 
+#define PDE_HASH_BITS 5
+#define PDE_HASH_SIZE (1 << PDE_HASH_BITS)
+
+static struct {
+	spinlock_t	 lock;
+	struct list_head head;
+} pde_openers[PDE_HASH_SIZE];
+
+static void __init pde_openers_init(void)
+{
+	int i;
+
+	for (i = 0; i < PDE_HASH_SIZE; i++) {
+		spin_lock_init(&pde_openers[i].lock);
+		INIT_LIST_HEAD(&pde_openers[i].head);
+	}
+}
+
 void __init proc_init_inodecache(void)
 {
+	pde_openers_init();
 	proc_inode_cachep = kmem_cache_create("proc_inode_cache",
 					     sizeof(struct proc_inode),
 					     0, (SLAB_RECLAIM_ACCOUNT|
@@ -126,18 +146,10 @@ static const struct super_operations pro
 	.show_options	= proc_show_options,
 };
 
-static void __pde_users_dec(struct proc_dir_entry *pde)
-{
-	pde->pde_users--;
-	if (pde->pde_unload_completion && pde->pde_users == 0)
-		complete(pde->pde_unload_completion);
-}
-
 void pde_users_dec(struct proc_dir_entry *pde)
 {
-	spin_lock(&pde->pde_unload_lock);
-	__pde_users_dec(pde);
-	spin_unlock(&pde->pde_unload_lock);
+	if (atomic_dec_and_test(&pde->pde_users) && pde->pde_unload_completion)
+		complete(pde->pde_unload_completion);
 }
 
 static loff_t proc_reg_llseek(struct file *file, loff_t offset, int whence)
@@ -145,27 +157,29 @@ static loff_t proc_reg_llseek(struct fil
 	struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
 	loff_t rv = -EINVAL;
 	loff_t (*llseek)(struct file *, loff_t, int);
+	const struct file_operations *fops;
 
-	spin_lock(&pde->pde_unload_lock);
+	rcu_read_lock();
+	fops = rcu_dereference(pde->proc_fops);
 	/*
 	 * remove_proc_entry() is going to delete PDE (as part of module
 	 * cleanup sequence). No new callers into module allowed.
 	 */
-	if (!pde->proc_fops) {
-		spin_unlock(&pde->pde_unload_lock);
+	if (!fops) {
+		rcu_read_unlock();
 		return rv;
 	}
 	/*
 	 * Bump refcount so that remove_proc_entry will wail for ->llseek to
 	 * complete.
 	 */
-	pde->pde_users++;
+	atomic_inc(&pde->pde_users);
 	/*
 	 * Save function pointer under lock, to protect against ->proc_fops
 	 * NULL'ifying right after ->pde_unload_lock is dropped.
 	 */
-	llseek = pde->proc_fops->llseek;
-	spin_unlock(&pde->pde_unload_lock);
+	llseek = fops->llseek;
+	rcu_read_unlock();
 
 	if (!llseek)
 		llseek = default_llseek;
@@ -180,15 +194,17 @@ static ssize_t proc_reg_read(struct file
 	struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
 	ssize_t rv = -EIO;
 	ssize_t (*read)(struct file *, char __user *, size_t, loff_t *);
+	const struct file_operations *fops;
 
-	spin_lock(&pde->pde_unload_lock);
-	if (!pde->proc_fops) {
-		spin_unlock(&pde->pde_unload_lock);
+	rcu_read_lock();
+	fops = rcu_dereference(pde->proc_fops);
+	if (!fops) {
+		rcu_read_unlock();
 		return rv;
 	}
-	pde->pde_users++;
-	read = pde->proc_fops->read;
-	spin_unlock(&pde->pde_unload_lock);
+	atomic_inc(&pde->pde_users);
+	read = fops->read;
+	rcu_read_unlock();
 
 	if (read)
 		rv = read(file, buf, count, ppos);
@@ -202,15 +218,17 @@ static ssize_t proc_reg_write(struct fil
 	struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
 	ssize_t rv = -EIO;
 	ssize_t (*write)(struct file *, const char __user *, size_t, loff_t *);
+	const struct file_operations *fops;
 
-	spin_lock(&pde->pde_unload_lock);
-	if (!pde->proc_fops) {
-		spin_unlock(&pde->pde_unload_lock);
+	rcu_read_lock();
+	fops = rcu_dereference(pde->proc_fops);
+	if (!fops) {
+		rcu_read_unlock();
 		return rv;
 	}
-	pde->pde_users++;
-	write = pde->proc_fops->write;
-	spin_unlock(&pde->pde_unload_lock);
+	atomic_inc(&pde->pde_users);
+	write = fops->write;
+	rcu_read_unlock();
 
 	if (write)
 		rv = write(file, buf, count, ppos);
@@ -224,15 +242,17 @@ static unsigned int proc_reg_poll(struct
 	struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
 	unsigned int rv = DEFAULT_POLLMASK;
 	unsigned int (*poll)(struct file *, struct poll_table_struct *);
+	const struct file_operations *fops;
 
-	spin_lock(&pde->pde_unload_lock);
-	if (!pde->proc_fops) {
-		spin_unlock(&pde->pde_unload_lock);
+	rcu_read_lock();
+	fops = rcu_dereference(pde->proc_fops);
+	if (!fops) {
+		rcu_read_unlock();
 		return rv;
 	}
-	pde->pde_users++;
-	poll = pde->proc_fops->poll;
-	spin_unlock(&pde->pde_unload_lock);
+	atomic_inc(&pde->pde_users);
+	poll = fops->poll;
+	rcu_read_unlock();
 
 	if (poll)
 		rv = poll(file, pts);
@@ -246,15 +266,17 @@ static long proc_reg_unlocked_ioctl(stru
 	struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
 	long rv = -ENOTTY;
 	long (*ioctl)(struct file *, unsigned int, unsigned long);
+	const struct file_operations *fops;
 
-	spin_lock(&pde->pde_unload_lock);
-	if (!pde->proc_fops) {
-		spin_unlock(&pde->pde_unload_lock);
+	rcu_read_lock();
+	fops = rcu_dereference(pde->proc_fops);
+	if (!fops) {
+		rcu_read_unlock();
 		return rv;
 	}
-	pde->pde_users++;
-	ioctl = pde->proc_fops->unlocked_ioctl;
-	spin_unlock(&pde->pde_unload_lock);
+	atomic_inc(&pde->pde_users);
+	ioctl = fops->unlocked_ioctl;
+	rcu_read_unlock();
 
 	if (ioctl)
 		rv = ioctl(file, cmd, arg);
@@ -269,15 +291,17 @@ static long proc_reg_compat_ioctl(struct
 	struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
 	long rv = -ENOTTY;
 	long (*compat_ioctl)(struct file *, unsigned int, unsigned long);
+	const struct file_operations *fops;
 
-	spin_lock(&pde->pde_unload_lock);
-	if (!pde->proc_fops) {
-		spin_unlock(&pde->pde_unload_lock);
+	rcu_read_lock();
+	fops = rcu_dereference(pde->proc_fops);
+	if (!fops) {
+		rcu_read_unlock();
 		return rv;
 	}
-	pde->pde_users++;
-	compat_ioctl = pde->proc_fops->compat_ioctl;
-	spin_unlock(&pde->pde_unload_lock);
+	atomic_inc(&pde->pde_users);
+	compat_ioctl = fops->compat_ioctl;
+	rcu_read_unlock();
 
 	if (compat_ioctl)
 		rv = compat_ioctl(file, cmd, arg);
@@ -292,15 +316,17 @@ static int proc_reg_mmap(struct file *fi
 	struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
 	int rv = -EIO;
 	int (*mmap)(struct file *, struct vm_area_struct *);
+	const struct file_operations *fops;
 
-	spin_lock(&pde->pde_unload_lock);
-	if (!pde->proc_fops) {
-		spin_unlock(&pde->pde_unload_lock);
+	rcu_read_lock();
+	fops = rcu_dereference(pde->proc_fops);
+	if (!fops) {
+		rcu_read_unlock();
 		return rv;
 	}
-	pde->pde_users++;
-	mmap = pde->proc_fops->mmap;
-	spin_unlock(&pde->pde_unload_lock);
+	atomic_inc(&pde->pde_users);
+	mmap = fops->mmap;
+	rcu_read_unlock();
 
 	if (mmap)
 		rv = mmap(file, vma);
@@ -309,6 +335,58 @@ static int proc_reg_mmap(struct file *fi
 	return rv;
 }
 
+static unsigned int pdeo_hash(const struct inode *inode, const struct file *file)
+{
+	unsigned long hashval = (unsigned long)inode ^ (unsigned long)file;
+
+	return hash_long(hashval, PDE_HASH_BITS);
+}
+
+static void pde_openers_add(struct pde_opener *pdeo)
+{
+	unsigned int slot = pdeo_hash(pdeo->inode, pdeo->file);
+
+	spin_lock(&pde_openers[slot].lock);
+	list_add(&pdeo->lh, &pde_openers[slot].head);
+	spin_unlock(&pde_openers[slot].lock);
+}
+
+void pde_openers_purge(struct proc_dir_entry *pde, struct list_head *queue)
+{
+	int i;
+	struct pde_opener *n, *pdeo;
+
+	for (i = 0; i < PDE_HASH_SIZE; i++) {
+		spin_lock(&pde_openers[i].lock);
+		list_for_each_entry_safe(pdeo, n, &pde_openers[i].head, lh) {
+			if (pdeo->pde == pde)
+				list_move(&pdeo->lh, queue);
+		}
+		spin_unlock(&pde_openers[i].lock);
+	}
+}
+
+typedef int (*release_t)(struct inode *, struct file *);
+
+static release_t pde_opener_del(struct inode *inode, struct file *file)
+{
+	unsigned int slot = pdeo_hash(inode, file);
+	struct pde_opener *pdeo;
+	release_t release = NULL;
+
+	spin_lock(&pde_openers[slot].lock);
+	list_for_each_entry(pdeo, &pde_openers[slot].head, lh) {
+		if (pdeo->inode == inode && pdeo->file == file) {
+			release = pdeo->release;
+			list_del(&pdeo->lh);
+			kfree(pdeo);
+			break;
+		}
+	}
+	spin_unlock(&pde_openers[slot].lock);
+	return release;
+}
+
 static int proc_reg_open(struct inode *inode, struct file *file)
 {
 	struct proc_dir_entry *pde = PDE(inode);
@@ -316,6 +394,7 @@ static int proc_reg_open(struct inode *i
 	int (*open)(struct inode *, struct file *);
 	int (*release)(struct inode *, struct file *);
 	struct pde_opener *pdeo;
+	const struct file_operations *fops;
 
 	/*
 	 * What for, you ask? Well, we can have open, rmmod, remove_proc_entry
@@ -331,57 +410,49 @@ static int proc_reg_open(struct inode *i
 	if (!pdeo)
 		return -ENOMEM;
 
-	spin_lock(&pde->pde_unload_lock);
-	if (!pde->proc_fops) {
-		spin_unlock(&pde->pde_unload_lock);
+	rcu_read_lock();
+	fops = rcu_dereference(pde->proc_fops);
+	if (!fops) {
+		rcu_read_unlock();
 		kfree(pdeo);
 		return -ENOENT;
 	}
-	pde->pde_users++;
-	open = pde->proc_fops->open;
-	release = pde->proc_fops->release;
-	spin_unlock(&pde->pde_unload_lock);
+	atomic_inc(&pde->pde_users);
+	open = fops->open;
+	release = fops->release;
+	rcu_read_unlock();
 
 	if (open)
 		rv = open(inode, file);
 
-	spin_lock(&pde->pde_unload_lock);
 	if (rv == 0 && release) {
 		/* To know what to release. */
 		pdeo->inode = inode;
 		pdeo->file = file;
+		pdeo->pde = pde;
 		/* Strictly for "too late" ->release in proc_reg_release(). */
 		pdeo->release = release;
-		list_add(&pdeo->lh, &pde->pde_openers);
-	} else
-		kfree(pdeo);
-	__pde_users_dec(pde);
-	spin_unlock(&pde->pde_unload_lock);
+		pde_openers_add(pdeo);
+		pdeo = NULL;
+	}
+	pde_users_dec(pde);
+	kfree(pdeo);
 	return rv;
 }
 
-static struct pde_opener *find_pde_opener(struct proc_dir_entry *pde,
-					struct inode *inode, struct file *file)
-{
-	struct pde_opener *pdeo;
-
-	list_for_each_entry(pdeo, &pde->pde_openers, lh) {
-		if (pdeo->inode == inode && pdeo->file == file)
-			return pdeo;
-	}
-	return NULL;
-}
 
 static int proc_reg_release(struct inode *inode, struct file *file)
 {
 	struct proc_dir_entry *pde = PDE(inode);
 	int rv = 0;
 	int (*release)(struct inode *, struct file *);
-	struct pde_opener *pdeo;
+	const struct file_operations *fops;
 
-	spin_lock(&pde->pde_unload_lock);
-	pdeo = find_pde_opener(pde, inode, file);
-	if (!pde->proc_fops) {
+	release = pde_opener_del(inode, file);
+	rcu_read_lock();
+	atomic_inc(&pde->pde_users);
+	fops = rcu_dereference(pde->proc_fops);
+	if (!fops) {
 		/*
 		 * Can't simply exit, __fput() will think that everything is OK,
 		 * and move on to freeing struct file. remove_proc_entry() will
@@ -390,22 +461,14 @@ static int proc_reg_release(struct inode
 		 *
 		 * But if opener is removed from list, who will ->release it?
 		 */
-		if (pdeo) {
-			list_del(&pdeo->lh);
-			spin_unlock(&pde->pde_unload_lock);
-			rv = pdeo->release(inode, file);
-			kfree(pdeo);
-		} else
-			spin_unlock(&pde->pde_unload_lock);
+		rcu_read_unlock();
+		if (release)
+			release(inode, file);
+		pde_users_dec(pde);
 		return rv;
 	}
-	pde->pde_users++;
-	release = pde->proc_fops->release;
-	if (pdeo) {
-		list_del(&pdeo->lh);
-		kfree(pdeo);
-	}
-	spin_unlock(&pde->pde_unload_lock);
+	release = fops->release;
+	rcu_read_unlock();
 
 	if (release)
 		rv = release(inode, file);
Index: linux/fs/proc/internal.h
===================================================================
--- linux.orig/fs/proc/internal.h	2012-10-24 09:01:07.299374618 -0500
+++ linux/fs/proc/internal.h	2012-10-24 09:12:13.986878345 -0500
@@ -145,12 +145,14 @@ int proc_readdir_de(struct proc_dir_entr
 		filldir_t filldir);
 
 struct pde_opener {
+	struct proc_dir_entry *pde;
 	struct inode *inode;
 	struct file *file;
 	int (*release)(struct inode *, struct file *);
 	struct list_head lh;
 };
 void pde_users_dec(struct proc_dir_entry *pde);
+void pde_openers_purge(struct proc_dir_entry *pde, struct list_head *queue);
 
 extern spinlock_t proc_subdir_lock;
 
Index: linux/include/linux/proc_fs.h
===================================================================
--- linux.orig/include/linux/proc_fs.h	2012-10-24 09:01:07.315374315 -0500
+++ linux/include/linux/proc_fs.h	2012-10-24 09:12:14.010877900 -0500
@@ -64,16 +64,14 @@ struct proc_dir_entry {
 	 * If you're allocating ->proc_fops dynamically, save a pointer
 	 * somewhere.
 	 */
-	const struct file_operations *proc_fops;
+	const struct file_operations __rcu *proc_fops;
 	struct proc_dir_entry *next, *parent, *subdir;
 	void *data;
 	read_proc_t *read_proc;
 	write_proc_t *write_proc;
 	atomic_t count;		/* use count */
-	int pde_users;	/* number of callers into module in progress */
 	struct completion *pde_unload_completion;
-	struct list_head pde_openers;	/* who did ->open, but not ->release */
-	spinlock_t pde_unload_lock; /* proc_fops checks and pde_users bumps */
+	atomic_t pde_users;	/* number of callers into module in progress */
 	u8 namelen;
 	char name[];
 };
--
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