Date:	Thu, 21 Feb 2013 23:06:11 -0800 (PST)
From:	Zheng Huai Cheng <zhenghc00@...il.com>
To:	fa.linux.kernel@...glegroups.com
Cc:	viro@...iv.linux.org.uk, eric.dumazet@...il.com,
	linux-kernel@...r.kernel.org, Nathan Zimmer <nzimmer@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	zhenghch@...ux.vnet.ibm.com
Subject: Re: [PATCH v3 resend] procfs: Improve Scaling in proc

在 2013年2月16日星期六UTC+8上午4时49分15秒，Nathan Zimmer写道：
> I am currently tracking a hotlock reported by a customer on a large system,
> 
> 512 cores.  I am currently running 3.8-rc7 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. However the pde_openers
> 
> list still is controlled by a spin lock. I tested on a 4096 machine and the lock
> 
> doesn't seem hot at least according to perf.
> 
> 
> 
> This is a refresh/resend of what was orignally suggested by Eric Dumazet some 
> 
> time ago.  
> 
> 
> 
> 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
> 
> 
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> 
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com> 
> 
> 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       |  58 +++++++++---------
> 
>  fs/proc/inode.c         | 156 ++++++++++++++++++++++++++----------------------
> 
>  include/linux/proc_fs.h |   6 +-
> 
>  3 files changed, 118 insertions(+), 102 deletions(-)
> 
> 
> 
> diff --git a/fs/proc/generic.c b/fs/proc/generic.c
> 
> index 76ddae8..6896a70 100644
> 
> --- a/fs/proc/generic.c
> 
> +++ b/fs/proc/generic.c
> 
> @@ -191,13 +191,16 @@ proc_file_read(struct file *file, char __user *buf, size_t nbytes,
> 
>  	struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
> 
>  	ssize_t rv = -EIO;
> 
>  
> 
> -	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();
> 
>  
> 
>  	rv = __proc_file_read(file, buf, nbytes, ppos);
> 
>  
> 
> @@ -213,13 +216,16 @@ proc_file_write(struct file *file, const char __user *buffer,
> 
>  	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);
> 
> @@ -558,7 +564,7 @@ static int proc_register(struct proc_dir_entry * dir, struct proc_dir_entry * dp
> 
>  
> 
>  	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++;
> 
> @@ -567,7 +573,7 @@ static int proc_register(struct proc_dir_entry * dir, struct proc_dir_entry * dp
> 
>  			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;
> 
>  	}
> 
> @@ -620,7 +626,8 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
> 
>  	ent->mode = mode;
> 
>  	ent->nlink = nlink;
> 
>  	atomic_set(&ent->count, 1);
> 
> -	spin_lock_init(&ent->pde_unload_lock);
> 
> +	atomic_set(&ent->pde_users, 1);
> 
> +	spin_lock_init(&ent->pde_openers_lock);
> 
>  	INIT_LIST_HEAD(&ent->pde_openers);
> 
>  out:
> 
>  	return ent;
> 
> @@ -744,7 +751,7 @@ struct proc_dir_entry *proc_create_data(const char *name, umode_t mode,
> 
>  	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;
> 
> @@ -802,37 +809,30 @@ void remove_proc_entry(const char *name, struct proc_dir_entry *parent)
> 
>  		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);
> 
> -
> 
> -		if (!de->pde_unload_completion)
> 
> -			de->pde_unload_completion = &c;
> 
>  
> 
> -		spin_unlock(&de->pde_unload_lock);
> 
> +	rcu_assign_pointer(de->proc_fops, NULL);
> 
> +	synchronize_rcu();
> 
> +	/* Wait until all existing callers into module are done. */
> 
>  
> 
> +	DECLARE_COMPLETION_ONSTACK(c);
> 
> +	de->pde_unload_completion = &c;
> 
> +	if (!atomic_dec_and_test(&de->pde_users))
> 
>  		wait_for_completion(de->pde_unload_completion);
> 
>  
> 
> -		spin_lock(&de->pde_unload_lock);
> 
> -	}
> 
> -
> 
> +	spin_lock(&de->pde_openers_lock);
> 
>  	while (!list_empty(&de->pde_openers)) {
> 
>  		struct pde_opener *pdeo;
> 
>  
> 
>  		pdeo = list_first_entry(&de->pde_openers, 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);
> 
> +	spin_unlock(&de->pde_openers_lock);
> 
>  
> 
>  	if (S_ISDIR(de->mode))
> 
>  		parent->nlink--;
> 
> diff --git a/fs/proc/inode.c b/fs/proc/inode.c
> 
> index 439ae688..031af27 100644
> 
> --- a/fs/proc/inode.c
> 
> +++ b/fs/proc/inode.c
> 
> @@ -128,46 +128,40 @@ static const struct super_operations proc_sops = {
> 
>  	.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)
> 
>  {
> 
> +	const struct file_operations *fops;
> 
>  	struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
> 
>  	loff_t rv = -EINVAL;
> 
>  	loff_t (*llseek)(struct file *, loff_t, int);
> 
>  
> 
> -	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;
> 
> @@ -182,15 +176,17 @@ static ssize_t proc_reg_read(struct file *file, char __user *buf, size_t count,
> 
>  	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);
> 
> @@ -204,15 +200,17 @@ static ssize_t proc_reg_write(struct file *file, const char __user *buf, size_t
> 
>  	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);
> 
> @@ -226,15 +224,17 @@ static unsigned int proc_reg_poll(struct file *file, struct poll_table_struct *p
> 
>  	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);
> 
> @@ -248,15 +248,17 @@ static long proc_reg_unlocked_ioctl(struct file *file, unsigned int cmd, unsigne
> 
>  	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);
> 
> @@ -271,15 +273,17 @@ static long proc_reg_compat_ioctl(struct file *file, unsigned int cmd, unsigned
> 
>  	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++;
> 
> +	atomic_inc(&pde->pde_users);
> 
>  	compat_ioctl = pde->proc_fops->compat_ioctl;
should this be compat_ioctl = fops->compat_ioctl ?

> 
> -	spin_unlock(&pde->pde_unload_lock);
> 
> +	rcu_read_unlock();
> 
>  
> 
>  	if (compat_ioctl)
> 
>  		rv = compat_ioctl(file, cmd, arg);
> 
> @@ -294,15 +298,17 @@ static int proc_reg_mmap(struct file *file, struct vm_area_struct *vma)
> 
>  	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++;
> 
> +	atomic_inc(&pde->pde_users);
> 
>  	mmap = pde->proc_fops->mmap;
also for this, should it be compat_ioctl = fops->compat_ioctl ?

> 
> -	spin_unlock(&pde->pde_unload_lock);
> 
> +	rcu_read_unlock();
> 
>  
> 
>  	if (mmap)
> 
>  		rv = mmap(file, vma);
> 
> @@ -318,6 +324,7 @@ static int proc_reg_open(struct inode *inode, struct file *file)
> 
>  	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
> 
> @@ -333,32 +340,33 @@ static int proc_reg_open(struct inode *inode, struct file *file)
> 
>  	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_lock();
> 
>  
> 
>  	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;
> 
>  		/* Strictly for "too late" ->release in proc_reg_release(). */
> 
>  		pdeo->release = release;
> 
> +		spin_lock(&pde->pde_openers_lock);
> 
>  		list_add(&pdeo->lh, &pde->pde_openers);
> 
> +		spin_unlock(&pde->pde_openers_lock);
> 
>  	} else
> 
>  		kfree(pdeo);
> 
> -	__pde_users_dec(pde);
> 
> -	spin_unlock(&pde->pde_unload_lock);
> 
> +	pde_users_dec(pde);
> 
>  	return rv;
> 
>  }
> 
>  
> 
> @@ -367,10 +375,14 @@ static struct pde_opener *find_pde_opener(struct proc_dir_entry *pde,
> 
>  {
> 
>  	struct pde_opener *pdeo;
> 
>  
> 
> +	spin_lock(&pde->pde_openers_lock);
> 
>  	list_for_each_entry(pdeo, &pde->pde_openers, lh) {
> 
> -		if (pdeo->inode == inode && pdeo->file == file)
> 
> +		if (pdeo->inode == inode && pdeo->file == file) {
> 
> +			spin_unlock(&pde->pde_openers_lock);
> 
>  			return pdeo;
> 
> +		}
> 
>  	}
> 
> +	spin_unlock(&pde->pde_openers_lock);
> 
>  	return NULL;
> 
>  }
> 
>  
> 
> @@ -380,10 +392,12 @@ static int proc_reg_release(struct inode *inode, struct file *file)
> 
>  	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) {
> 
> +	rcu_read_lock();
> 
> +	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
> 
> @@ -393,21 +407,23 @@ static int proc_reg_release(struct inode *inode, struct file *file)
> 
>  		 * But if opener is removed from list, who will ->release it?
> 
>  		 */
> 
>  		if (pdeo) {
> 
> +			spin_lock(&pde->pde_openers_lock);
> 
>  			list_del(&pdeo->lh);
> 
> -			spin_unlock(&pde->pde_unload_lock);
> 
> +			spin_unlock(&pde->pde_openers_lock);
> 
>  			rv = pdeo->release(inode, file);
> 
>  			kfree(pdeo);
> 
> -		} else
> 
> -			spin_unlock(&pde->pde_unload_lock);
> 
> +		}
> 
>  		return rv;
> 
>  	}
> 
> -	pde->pde_users++;
> 
> -	release = pde->proc_fops->release;
> 
> +	atomic_inc(&pde->pde_users);
> 
> +	release = fops->release;
> 
> +	rcu_read_unlock();
> 
>  	if (pdeo) {
> 
> +		spin_lock(&pde->pde_openers_lock);
> 
>  		list_del(&pdeo->lh);
> 
> -		kfree(pdeo);
> 
> +		spin_unlock(&pde->pde_openers_lock);
> 
>  	}
> 
> -	spin_unlock(&pde->pde_unload_lock);
> 
> +	kfree(pdeo);
> 
>  
> 
>  	if (release)
> 
>  		rv = release(inode, file);
> 
> diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
> 
> index 32676b3..82628d9 100644
> 
> --- a/include/linux/proc_fs.h
> 
> +++ b/include/linux/proc_fs.h
> 
> @@ -68,16 +68,16 @@ 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 */
> 
> +	atomic_t pde_users;	/* number of callers into module in progress */
> 
>  	struct completion *pde_unload_completion;
> 
> +	spinlock_t pde_openers_lock;
> 
>  	struct list_head pde_openers;	/* who did ->open, but not ->release */
> 
> -	spinlock_t pde_unload_lock; /* proc_fops checks and pde_users bumps */
> 
>  	u8 namelen;
> 
>  	char name[];
> 
>  };
> 
> -- 
> 
> 1.8.1.2
> 
> 
> 
> --
> 
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