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Date:   Thu, 8 Nov 2018 15:26:59 -0500
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     NeilBrown <neilb@suse.com>
Cc:     Jeff Layton <jlayton@kernel.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Martin Wilck <mwilck@suse.de>, linux-fsdevel@vger.kernel.org,
        Frank Filz <ffilzlnx@mindspring.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 01/12] fs/locks: rename some lists and pointers.
Message-ID: <20181108202659.GD6090@fieldses.org>
References: <154138128401.31651.1381177427603557514.stgit@noble>
 <154138144767.31651.11225349164396042986.stgit@noble>
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On Mon, Nov 05, 2018 at 12:30:47PM +1100, NeilBrown wrote:
> struct file lock contains an 'fl_next' pointer which
> is used to point to the lock that this request is blocked
> waiting for.  So rename it to fl_blocker.
> 
> The fl_blocked list_head in an active lock is the head of a list of
> blocked requests.  In a request it is a node in that list.
> These are two distinct uses, so replace with two list_heads
> with different names.
> fl_blocked is the head of a list of blocked requests
> fl_block is a node on that list.

Reading these, I have a lot of trouble keeping fl_blocked, fl_block, and
fl_blocker straight.  Is it just me?

I guess they form a tree, so fl_children, fl_siblings, and fl_parent
might be easier for me to keep straight.

--b.

> 
> The two different list_heads are never used at the same time, but that
> will change in a future patch.
> 
> Note that a tracepoint is changed to report fl_blocker instead
> of fl_next.
> 
> Signed-off-by: NeilBrown <neilb@suse.com>
> ---
>  fs/cifs/file.c                  |    2 +-
>  fs/locks.c                      |   38 ++++++++++++++++++++------------------
>  include/linux/fs.h              |    7 +++++--
>  include/trace/events/filelock.h |   16 ++++++++--------
>  4 files changed, 34 insertions(+), 29 deletions(-)
> 
> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> index 74c33d5fafc8..d7ed895e05d1 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -1103,7 +1103,7 @@ cifs_posix_lock_set(struct file *file, struct file_lock *flock)
>  	rc = posix_lock_file(file, flock, NULL);
>  	up_write(&cinode->lock_sem);
>  	if (rc == FILE_LOCK_DEFERRED) {
> -		rc = wait_event_interruptible(flock->fl_wait, !flock->fl_next);
> +		rc = wait_event_interruptible(flock->fl_wait, !flock->fl_blocker);
>  		if (!rc)
>  			goto try_again;
>  		posix_unblock_lock(flock);
> diff --git a/fs/locks.c b/fs/locks.c
> index 2ecb4db8c840..a6c6d601286c 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -189,7 +189,7 @@ static DEFINE_HASHTABLE(blocked_hash, BLOCKED_HASH_BITS);
>   * This lock protects the blocked_hash. Generally, if you're accessing it, you
>   * want to be holding this lock.
>   *
> - * In addition, it also protects the fl->fl_block list, and the fl->fl_next
> + * In addition, it also protects the fl->fl_blocked list, and the fl->fl_blocker
>   * pointer for file_lock structures that are acting as lock requests (in
>   * contrast to those that are acting as records of acquired locks).
>   *
> @@ -293,6 +293,7 @@ static void locks_init_lock_heads(struct file_lock *fl)
>  {
>  	INIT_HLIST_NODE(&fl->fl_link);
>  	INIT_LIST_HEAD(&fl->fl_list);
> +	INIT_LIST_HEAD(&fl->fl_blocked);
>  	INIT_LIST_HEAD(&fl->fl_block);
>  	init_waitqueue_head(&fl->fl_wait);
>  }
> @@ -332,6 +333,7 @@ void locks_free_lock(struct file_lock *fl)
>  {
>  	BUG_ON(waitqueue_active(&fl->fl_wait));
>  	BUG_ON(!list_empty(&fl->fl_list));
> +	BUG_ON(!list_empty(&fl->fl_blocked));
>  	BUG_ON(!list_empty(&fl->fl_block));
>  	BUG_ON(!hlist_unhashed(&fl->fl_link));
>  
> @@ -667,7 +669,7 @@ static void __locks_delete_block(struct file_lock *waiter)
>  {
>  	locks_delete_global_blocked(waiter);
>  	list_del_init(&waiter->fl_block);
> -	waiter->fl_next = NULL;
> +	waiter->fl_blocker = NULL;
>  }
>  
>  static void locks_delete_block(struct file_lock *waiter)
> @@ -683,16 +685,16 @@ static void locks_delete_block(struct file_lock *waiter)
>   * it seems like the reasonable thing to do.
>   *
>   * Must be called with both the flc_lock and blocked_lock_lock held. The
> - * fl_block list itself is protected by the blocked_lock_lock, but by ensuring
> + * fl_blocked list itself is protected by the blocked_lock_lock, but by ensuring
>   * that the flc_lock is also held on insertions we can avoid taking the
> - * blocked_lock_lock in some cases when we see that the fl_block list is empty.
> + * blocked_lock_lock in some cases when we see that the fl_blocked list is empty.
>   */
>  static void __locks_insert_block(struct file_lock *blocker,
>  					struct file_lock *waiter)
>  {
>  	BUG_ON(!list_empty(&waiter->fl_block));
> -	waiter->fl_next = blocker;
> -	list_add_tail(&waiter->fl_block, &blocker->fl_block);
> +	waiter->fl_blocker = blocker;
> +	list_add_tail(&waiter->fl_block, &blocker->fl_blocked);
>  	if (IS_POSIX(blocker) && !IS_OFDLCK(blocker))
>  		locks_insert_global_blocked(waiter);
>  }
> @@ -716,18 +718,18 @@ static void locks_wake_up_blocks(struct file_lock *blocker)
>  	/*
>  	 * Avoid taking global lock if list is empty. This is safe since new
>  	 * blocked requests are only added to the list under the flc_lock, and
> -	 * the flc_lock is always held here. Note that removal from the fl_block
> +	 * the flc_lock is always held here. Note that removal from the fl_blocked
>  	 * list does not require the flc_lock, so we must recheck list_empty()
>  	 * after acquiring the blocked_lock_lock.
>  	 */
> -	if (list_empty(&blocker->fl_block))
> +	if (list_empty(&blocker->fl_blocked))
>  		return;
>  
>  	spin_lock(&blocked_lock_lock);
> -	while (!list_empty(&blocker->fl_block)) {
> +	while (!list_empty(&blocker->fl_blocked)) {
>  		struct file_lock *waiter;
>  
> -		waiter = list_first_entry(&blocker->fl_block,
> +		waiter = list_first_entry(&blocker->fl_blocked,
>  				struct file_lock, fl_block);
>  		__locks_delete_block(waiter);
>  		if (waiter->fl_lmops && waiter->fl_lmops->lm_notify)
> @@ -878,7 +880,7 @@ static struct file_lock *what_owner_is_waiting_for(struct file_lock *block_fl)
>  
>  	hash_for_each_possible(blocked_hash, fl, fl_link, posix_owner_key(block_fl)) {
>  		if (posix_same_owner(fl, block_fl))
> -			return fl->fl_next;
> +			return fl->fl_blocker;
>  	}
>  	return NULL;
>  }
> @@ -1237,7 +1239,7 @@ static int posix_lock_inode_wait(struct inode *inode, struct file_lock *fl)
>  		error = posix_lock_inode(inode, fl, NULL);
>  		if (error != FILE_LOCK_DEFERRED)
>  			break;
> -		error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
> +		error = wait_event_interruptible(fl->fl_wait, !fl->fl_blocker);
>  		if (!error)
>  			continue;
>  
> @@ -1324,7 +1326,7 @@ int locks_mandatory_area(struct inode *inode, struct file *filp, loff_t start,
>  		error = posix_lock_inode(inode, &fl, NULL);
>  		if (error != FILE_LOCK_DEFERRED)
>  			break;
> -		error = wait_event_interruptible(fl.fl_wait, !fl.fl_next);
> +		error = wait_event_interruptible(fl.fl_wait, !fl.fl_blocker);
>  		if (!error) {
>  			/*
>  			 * If we've been sleeping someone might have
> @@ -1518,7 +1520,7 @@ int __break_lease(struct inode *inode, unsigned int mode, unsigned int type)
>  
>  	locks_dispose_list(&dispose);
>  	error = wait_event_interruptible_timeout(new_fl->fl_wait,
> -						!new_fl->fl_next, break_time);
> +						!new_fl->fl_blocker, break_time);
>  
>  	percpu_down_read_preempt_disable(&file_rwsem);
>  	spin_lock(&ctx->flc_lock);
> @@ -1931,7 +1933,7 @@ static int flock_lock_inode_wait(struct inode *inode, struct file_lock *fl)
>  		error = flock_lock_inode(inode, fl);
>  		if (error != FILE_LOCK_DEFERRED)
>  			break;
> -		error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
> +		error = wait_event_interruptible(fl->fl_wait, !fl->fl_blocker);
>  		if (!error)
>  			continue;
>  
> @@ -2210,7 +2212,7 @@ static int do_lock_file_wait(struct file *filp, unsigned int cmd,
>  		error = vfs_lock_file(filp, cmd, fl, NULL);
>  		if (error != FILE_LOCK_DEFERRED)
>  			break;
> -		error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
> +		error = wait_event_interruptible(fl->fl_wait, !fl->fl_blocker);
>  		if (!error)
>  			continue;
>  
> @@ -2581,7 +2583,7 @@ posix_unblock_lock(struct file_lock *waiter)
>  	int status = 0;
>  
>  	spin_lock(&blocked_lock_lock);
> -	if (waiter->fl_next)
> +	if (waiter->fl_blocker)
>  		__locks_delete_block(waiter);
>  	else
>  		status = -ENOENT;
> @@ -2707,7 +2709,7 @@ static int locks_show(struct seq_file *f, void *v)
>  
>  	lock_get_status(f, fl, iter->li_pos, "");
>  
> -	list_for_each_entry(bfl, &fl->fl_block, fl_block)
> +	list_for_each_entry(bfl, &fl->fl_blocked, fl_block)
>  		lock_get_status(f, bfl, iter->li_pos, " ->");
>  
>  	return 0;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index c95c0807471f..a161bcdca8a2 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1044,10 +1044,13 @@ bool opens_in_grace(struct net *);
>   * Obviously, the last two criteria only matter for POSIX locks.
>   */
>  struct file_lock {
> -	struct file_lock *fl_next;	/* singly linked list for this inode  */
> +	struct file_lock *fl_blocker;	/* The lock, that is blocking us */
>  	struct list_head fl_list;	/* link into file_lock_context */
>  	struct hlist_node fl_link;	/* node in global lists */
> -	struct list_head fl_block;	/* circular list of blocked processes */
> +	struct list_head fl_blocked;	/* list of requests with
> +					 * ->fl_blocker pointing here */
> +	struct list_head fl_block;	/* node in
> +					 * ->fl_blocker->fl_blocked */
>  	fl_owner_t fl_owner;
>  	unsigned int fl_flags;
>  	unsigned char fl_type;
> diff --git a/include/trace/events/filelock.h b/include/trace/events/filelock.h
> index 68b17c116907..fad7befa612d 100644
> --- a/include/trace/events/filelock.h
> +++ b/include/trace/events/filelock.h
> @@ -68,7 +68,7 @@ DECLARE_EVENT_CLASS(filelock_lock,
>  		__field(struct file_lock *, fl)
>  		__field(unsigned long, i_ino)
>  		__field(dev_t, s_dev)
> -		__field(struct file_lock *, fl_next)
> +		__field(struct file_lock *, fl_blocker)
>  		__field(fl_owner_t, fl_owner)
>  		__field(unsigned int, fl_pid)
>  		__field(unsigned int, fl_flags)
> @@ -82,7 +82,7 @@ DECLARE_EVENT_CLASS(filelock_lock,
>  		__entry->fl = fl ? fl : NULL;
>  		__entry->s_dev = inode->i_sb->s_dev;
>  		__entry->i_ino = inode->i_ino;
> -		__entry->fl_next = fl ? fl->fl_next : NULL;
> +		__entry->fl_blocker = fl ? fl->fl_blocker : NULL;
>  		__entry->fl_owner = fl ? fl->fl_owner : NULL;
>  		__entry->fl_pid = fl ? fl->fl_pid : 0;
>  		__entry->fl_flags = fl ? fl->fl_flags : 0;
> @@ -92,9 +92,9 @@ DECLARE_EVENT_CLASS(filelock_lock,
>  		__entry->ret = ret;
>  	),
>  
> -	TP_printk("fl=0x%p dev=0x%x:0x%x ino=0x%lx fl_next=0x%p fl_owner=0x%p fl_pid=%u fl_flags=%s fl_type=%s fl_start=%lld fl_end=%lld ret=%d",
> +	TP_printk("fl=0x%p dev=0x%x:0x%x ino=0x%lx fl_blocker=0x%p fl_owner=0x%p fl_pid=%u fl_flags=%s fl_type=%s fl_start=%lld fl_end=%lld ret=%d",
>  		__entry->fl, MAJOR(__entry->s_dev), MINOR(__entry->s_dev),
> -		__entry->i_ino, __entry->fl_next, __entry->fl_owner,
> +		__entry->i_ino, __entry->fl_blocker, __entry->fl_owner,
>  		__entry->fl_pid, show_fl_flags(__entry->fl_flags),
>  		show_fl_type(__entry->fl_type),
>  		__entry->fl_start, __entry->fl_end, __entry->ret)
> @@ -125,7 +125,7 @@ DECLARE_EVENT_CLASS(filelock_lease,
>  		__field(struct file_lock *, fl)
>  		__field(unsigned long, i_ino)
>  		__field(dev_t, s_dev)
> -		__field(struct file_lock *, fl_next)
> +		__field(struct file_lock *, fl_blocker)
>  		__field(fl_owner_t, fl_owner)
>  		__field(unsigned int, fl_flags)
>  		__field(unsigned char, fl_type)
> @@ -137,7 +137,7 @@ DECLARE_EVENT_CLASS(filelock_lease,
>  		__entry->fl = fl ? fl : NULL;
>  		__entry->s_dev = inode->i_sb->s_dev;
>  		__entry->i_ino = inode->i_ino;
> -		__entry->fl_next = fl ? fl->fl_next : NULL;
> +		__entry->fl_blocker = fl ? fl->fl_blocker : NULL;
>  		__entry->fl_owner = fl ? fl->fl_owner : NULL;
>  		__entry->fl_flags = fl ? fl->fl_flags : 0;
>  		__entry->fl_type = fl ? fl->fl_type : 0;
> @@ -145,9 +145,9 @@ DECLARE_EVENT_CLASS(filelock_lease,
>  		__entry->fl_downgrade_time = fl ? fl->fl_downgrade_time : 0;
>  	),
>  
> -	TP_printk("fl=0x%p dev=0x%x:0x%x ino=0x%lx fl_next=0x%p fl_owner=0x%p fl_flags=%s fl_type=%s fl_break_time=%lu fl_downgrade_time=%lu",
> +	TP_printk("fl=0x%p dev=0x%x:0x%x ino=0x%lx fl_blocker=0x%p fl_owner=0x%p fl_flags=%s fl_type=%s fl_break_time=%lu fl_downgrade_time=%lu",
>  		__entry->fl, MAJOR(__entry->s_dev), MINOR(__entry->s_dev),
> -		__entry->i_ino, __entry->fl_next, __entry->fl_owner,
> +		__entry->i_ino, __entry->fl_blocker, __entry->fl_owner,
>  		show_fl_flags(__entry->fl_flags),
>  		show_fl_type(__entry->fl_type),
>  		__entry->fl_break_time, __entry->fl_downgrade_time)
>