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From: Guenter Roeck <linux@roeck-us.net>
To: Jan Kara <jack@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-fsdevel@vger.kernel.org,
	Miklos Szeredi <mszeredi@redhat.com>,
	Lino Sanfilippo <LinoSanfilippo@gmx.de>,
	Eric Paris <eparis@redhat.com>
Subject: Re: [PATCH 4/6] fsnotify: Convert notification_mutex to a spinlock
Date: Fri, 16 Sep 2016 08:55:03 -0700
Message-ID: <20160916155503.GA1651@roeck-us.net> (raw)
In-Reply-To: <1474031567-1831-1-git-send-email-jack@suse.cz>

On Fri, Sep 16, 2016 at 03:12:47PM +0200, Jan Kara wrote:
> notification_mutex is used to protect the list of pending events. As
> such there's no reason to use a sleeping lock for it. Convert it to a
> spinlock.
> 
> Reviewed-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
> Signed-off-by: Jan Kara <jack@suse.cz>

Tested-by: Guenter Roeck <linux@roeck-us.net>

> ---
>  fs/notify/fanotify/fanotify_user.c | 27 ++++++++++++++-------------
>  fs/notify/group.c                  |  6 +++---
>  fs/notify/inotify/inotify_user.c   | 16 ++++++++--------
>  fs/notify/notification.c           | 27 +++++++++++++++------------
>  include/linux/fsnotify_backend.h   |  2 +-
>  5 files changed, 41 insertions(+), 37 deletions(-)
> 
> This is a fixed version of the patch that fixes the BUG_ON hitting on UP
> kernels.
> 
> diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> index 46d135c4988f..80091a5dc8c0 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -49,12 +49,13 @@ struct kmem_cache *fanotify_perm_event_cachep __read_mostly;
>   * enough to fit in "count". Return an error pointer if the count
>   * is not large enough.
>   *
> - * Called with the group->notification_mutex held.
> + * Called with the group->notification_lock held.
>   */
>  static struct fsnotify_event *get_one_event(struct fsnotify_group *group,
>  					    size_t count)
>  {
> -	BUG_ON(!mutex_is_locked(&group->notification_mutex));
> +	BUG_ON(IS_ENABLED(CONFIG_SMP) &&
> +	       !spin_is_locked(&group->notification_lock));
>  
>  	pr_debug("%s: group=%p count=%zd\n", __func__, group, count);
>  
> @@ -64,7 +65,7 @@ static struct fsnotify_event *get_one_event(struct fsnotify_group *group,
>  	if (FAN_EVENT_METADATA_LEN > count)
>  		return ERR_PTR(-EINVAL);
>  
> -	/* held the notification_mutex the whole time, so this is the
> +	/* held the notification_lock the whole time, so this is the
>  	 * same event we peeked above */
>  	return fsnotify_remove_first_event(group);
>  }
> @@ -244,10 +245,10 @@ static unsigned int fanotify_poll(struct file *file, poll_table *wait)
>  	int ret = 0;
>  
>  	poll_wait(file, &group->notification_waitq, wait);
> -	mutex_lock(&group->notification_mutex);
> +	spin_lock(&group->notification_lock);
>  	if (!fsnotify_notify_queue_is_empty(group))
>  		ret = POLLIN | POLLRDNORM;
> -	mutex_unlock(&group->notification_mutex);
> +	spin_unlock(&group->notification_lock);
>  
>  	return ret;
>  }
> @@ -268,9 +269,9 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
>  
>  	add_wait_queue(&group->notification_waitq, &wait);
>  	while (1) {
> -		mutex_lock(&group->notification_mutex);
> +		spin_lock(&group->notification_lock);
>  		kevent = get_one_event(group, count);
> -		mutex_unlock(&group->notification_mutex);
> +		spin_unlock(&group->notification_lock);
>  
>  		if (IS_ERR(kevent)) {
>  			ret = PTR_ERR(kevent);
> @@ -387,17 +388,17 @@ static int fanotify_release(struct inode *ignored, struct file *file)
>  	 * dequeue them and set the response. They will be freed once the
>  	 * response is consumed and fanotify_get_response() returns.
>  	 */
> -	mutex_lock(&group->notification_mutex);
> +	spin_lock(&group->notification_lock);
>  	while (!fsnotify_notify_queue_is_empty(group)) {
>  		fsn_event = fsnotify_remove_first_event(group);
>  		if (!(fsn_event->mask & FAN_ALL_PERM_EVENTS)) {
> -			mutex_unlock(&group->notification_mutex);
> +			spin_unlock(&group->notification_lock);
>  			fsnotify_destroy_event(group, fsn_event);
> -			mutex_lock(&group->notification_mutex);
> +			spin_lock(&group->notification_lock);
>  		} else
>  			FANOTIFY_PE(fsn_event)->response = FAN_ALLOW;
>  	}
> -	mutex_unlock(&group->notification_mutex);
> +	spin_unlock(&group->notification_lock);
>  
>  	/* Response for all permission events it set, wakeup waiters */
>  	wake_up(&group->fanotify_data.access_waitq);
> @@ -423,10 +424,10 @@ static long fanotify_ioctl(struct file *file, unsigned int cmd, unsigned long ar
>  
>  	switch (cmd) {
>  	case FIONREAD:
> -		mutex_lock(&group->notification_mutex);
> +		spin_lock(&group->notification_lock);
>  		list_for_each_entry(fsn_event, &group->notification_list, list)
>  			send_len += FAN_EVENT_METADATA_LEN;
> -		mutex_unlock(&group->notification_mutex);
> +		spin_unlock(&group->notification_lock);
>  		ret = put_user(send_len, (int __user *) p);
>  		break;
>  	}
> diff --git a/fs/notify/group.c b/fs/notify/group.c
> index b47f7cfdcaa4..fbe3cbebec16 100644
> --- a/fs/notify/group.c
> +++ b/fs/notify/group.c
> @@ -45,9 +45,9 @@ static void fsnotify_final_destroy_group(struct fsnotify_group *group)
>   */
>  void fsnotify_group_stop_queueing(struct fsnotify_group *group)
>  {
> -	mutex_lock(&group->notification_mutex);
> +	spin_lock(&group->notification_lock);
>  	group->shutdown = true;
> -	mutex_unlock(&group->notification_mutex);
> +	spin_unlock(&group->notification_lock);
>  }
>  
>  /*
> @@ -125,7 +125,7 @@ struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops)
>  	atomic_set(&group->refcnt, 1);
>  	atomic_set(&group->num_marks, 0);
>  
> -	mutex_init(&group->notification_mutex);
> +	spin_lock_init(&group->notification_lock);
>  	INIT_LIST_HEAD(&group->notification_list);
>  	init_waitqueue_head(&group->notification_waitq);
>  	group->max_events = UINT_MAX;
> diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
> index b8d08d0d0a4d..69d1ea3d292a 100644
> --- a/fs/notify/inotify/inotify_user.c
> +++ b/fs/notify/inotify/inotify_user.c
> @@ -115,10 +115,10 @@ static unsigned int inotify_poll(struct file *file, poll_table *wait)
>  	int ret = 0;
>  
>  	poll_wait(file, &group->notification_waitq, wait);
> -	mutex_lock(&group->notification_mutex);
> +	spin_lock(&group->notification_lock);
>  	if (!fsnotify_notify_queue_is_empty(group))
>  		ret = POLLIN | POLLRDNORM;
> -	mutex_unlock(&group->notification_mutex);
> +	spin_unlock(&group->notification_lock);
>  
>  	return ret;
>  }
> @@ -138,7 +138,7 @@ static int round_event_name_len(struct fsnotify_event *fsn_event)
>   * enough to fit in "count". Return an error pointer if
>   * not large enough.
>   *
> - * Called with the group->notification_mutex held.
> + * Called with the group->notification_lock held.
>   */
>  static struct fsnotify_event *get_one_event(struct fsnotify_group *group,
>  					    size_t count)
> @@ -157,7 +157,7 @@ static struct fsnotify_event *get_one_event(struct fsnotify_group *group,
>  	if (event_size > count)
>  		return ERR_PTR(-EINVAL);
>  
> -	/* held the notification_mutex the whole time, so this is the
> +	/* held the notification_lock the whole time, so this is the
>  	 * same event we peeked above */
>  	fsnotify_remove_first_event(group);
>  
> @@ -234,9 +234,9 @@ static ssize_t inotify_read(struct file *file, char __user *buf,
>  
>  	add_wait_queue(&group->notification_waitq, &wait);
>  	while (1) {
> -		mutex_lock(&group->notification_mutex);
> +		spin_lock(&group->notification_lock);
>  		kevent = get_one_event(group, count);
> -		mutex_unlock(&group->notification_mutex);
> +		spin_unlock(&group->notification_lock);
>  
>  		pr_debug("%s: group=%p kevent=%p\n", __func__, group, kevent);
>  
> @@ -300,13 +300,13 @@ static long inotify_ioctl(struct file *file, unsigned int cmd,
>  
>  	switch (cmd) {
>  	case FIONREAD:
> -		mutex_lock(&group->notification_mutex);
> +		spin_lock(&group->notification_lock);
>  		list_for_each_entry(fsn_event, &group->notification_list,
>  				    list) {
>  			send_len += sizeof(struct inotify_event);
>  			send_len += round_event_name_len(fsn_event);
>  		}
> -		mutex_unlock(&group->notification_mutex);
> +		spin_unlock(&group->notification_lock);
>  		ret = put_user(send_len, (int __user *) p);
>  		break;
>  	}
> diff --git a/fs/notify/notification.c b/fs/notify/notification.c
> index 7d563dea52a4..8a7a8cd041e8 100644
> --- a/fs/notify/notification.c
> +++ b/fs/notify/notification.c
> @@ -63,7 +63,8 @@ EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
>  /* return true if the notify queue is empty, false otherwise */
>  bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
>  {
> -	BUG_ON(!mutex_is_locked(&group->notification_mutex));
> +	BUG_ON(IS_ENABLED(CONFIG_SMP) &&
> +	       !spin_is_locked(&group->notification_lock));
>  	return list_empty(&group->notification_list) ? true : false;
>  }
>  
> @@ -95,10 +96,10 @@ int fsnotify_add_event(struct fsnotify_group *group,
>  
>  	pr_debug("%s: group=%p event=%p\n", __func__, group, event);
>  
> -	mutex_lock(&group->notification_mutex);
> +	spin_lock(&group->notification_lock);
>  
>  	if (group->shutdown) {
> -		mutex_unlock(&group->notification_mutex);
> +		spin_unlock(&group->notification_lock);
>  		return 2;
>  	}
>  
> @@ -106,7 +107,7 @@ int fsnotify_add_event(struct fsnotify_group *group,
>  		ret = 2;
>  		/* Queue overflow event only if it isn't already queued */
>  		if (!list_empty(&group->overflow_event->list)) {
> -			mutex_unlock(&group->notification_mutex);
> +			spin_unlock(&group->notification_lock);
>  			return ret;
>  		}
>  		event = group->overflow_event;
> @@ -116,7 +117,7 @@ int fsnotify_add_event(struct fsnotify_group *group,
>  	if (!list_empty(list) && merge) {
>  		ret = merge(list, event);
>  		if (ret) {
> -			mutex_unlock(&group->notification_mutex);
> +			spin_unlock(&group->notification_lock);
>  			return ret;
>  		}
>  	}
> @@ -124,7 +125,7 @@ int fsnotify_add_event(struct fsnotify_group *group,
>  queue:
>  	group->q_len++;
>  	list_add_tail(&event->list, list);
> -	mutex_unlock(&group->notification_mutex);
> +	spin_unlock(&group->notification_lock);
>  
>  	wake_up(&group->notification_waitq);
>  	kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
> @@ -139,7 +140,8 @@ struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
>  {
>  	struct fsnotify_event *event;
>  
> -	BUG_ON(!mutex_is_locked(&group->notification_mutex));
> +	BUG_ON(IS_ENABLED(CONFIG_SMP) &&
> +	       !spin_is_locked(&group->notification_lock));
>  
>  	pr_debug("%s: group=%p\n", __func__, group);
>  
> @@ -161,7 +163,8 @@ struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
>   */
>  struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
>  {
> -	BUG_ON(!mutex_is_locked(&group->notification_mutex));
> +	BUG_ON(IS_ENABLED(CONFIG_SMP) &&
> +	       !spin_is_locked(&group->notification_lock));
>  
>  	return list_first_entry(&group->notification_list,
>  				struct fsnotify_event, list);
> @@ -175,14 +178,14 @@ void fsnotify_flush_notify(struct fsnotify_group *group)
>  {
>  	struct fsnotify_event *event;
>  
> -	mutex_lock(&group->notification_mutex);
> +	spin_lock(&group->notification_lock);
>  	while (!fsnotify_notify_queue_is_empty(group)) {
>  		event = fsnotify_remove_first_event(group);
> -		mutex_unlock(&group->notification_mutex);
> +		spin_unlock(&group->notification_lock);
>  		fsnotify_destroy_event(group, event);
> -		mutex_lock(&group->notification_mutex);
> +		spin_lock(&group->notification_lock);
>  	}
> -	mutex_unlock(&group->notification_mutex);
> +	spin_unlock(&group->notification_lock);
>  }
>  
>  /*
> diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
> index 7268ed076be8..0713e873b1c9 100644
> --- a/include/linux/fsnotify_backend.h
> +++ b/include/linux/fsnotify_backend.h
> @@ -135,7 +135,7 @@ struct fsnotify_group {
>  	const struct fsnotify_ops *ops;	/* how this group handles things */
>  
>  	/* needed to send notification to userspace */
> -	struct mutex notification_mutex;	/* protect the notification_list */
> +	spinlock_t notification_lock;		/* protect the notification_list */
>  	struct list_head notification_list;	/* list of event_holder this group needs to send to userspace */
>  	wait_queue_head_t notification_waitq;	/* read() on the notification file blocks on this waitq */
>  	unsigned int q_len;			/* events on the queue */
> -- 
> 2.6.6
> 

  reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-16 13:12 Jan Kara
2016-09-16 15:55 ` Guenter Roeck [this message]
  -- strict thread matches above, loose matches on Subject: below --
2016-09-13 20:15 [PATCH 0/6 v2] fsnotify: Fix list corruption for permission events Jan Kara
2016-09-13 20:15 ` [PATCH 4/6] fsnotify: Convert notification_mutex to a spinlock Jan Kara
2016-09-14 17:13   ` Lino Sanfilippo

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