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Date:   Wed, 8 Aug 2018 15:07:39 -0400
From:   "J. Bruce Fields" <bfields@...ldses.org>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     NeilBrown <neilb@...e.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Martin Wilck <mwilck@...e.de>
Subject: Re: [PATCH 1/4] fs/locks: rename some lists and pointers.

On Wed, Aug 08, 2018 at 06:47:34AM -0400, Jeff Layton wrote:
> On Wed, 2018-08-08 at 11:51 +1000, 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.
> > 
> > This separation will be used in the next patch.
> > 
> > Note that a tracepoint is changed to report fl_blocker instead
> > of fl_next.  Might this be an ABI breakage?
> > 
> 
> My understanding (possibly wrong) is that because tracepoints are
> exposed via debugfs, they aren't considered part of the ABI.

Wasn't there an incident where tracepoint changes had to be reverted for
powertop?

The chances of breaking an equivalent utility in this case are small, I
think, I'm fine with trying it.

--b.

> 
> Thanks for the patches, Neil. I'll go over them in detail soon.
> 
> > Signed-off-by: NeilBrown <neilb@...e.com>
> > ---
> >  fs/cifs/file.c                  |    2 +-
> >  fs/locks.c                      |   40 ++++++++++++++++++++-------------------
> >  include/linux/fs.h              |    5 +++--
> >  include/trace/events/filelock.h |   16 ++++++++--------
> >  4 files changed, 33 insertions(+), 30 deletions(-)
> > 
> > diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> > index 8d41ca7bfcf1..066ed2e4ba96 100644
> > --- a/fs/cifs/file.c
> > +++ b/fs/cifs/file.c
> > @@ -1092,7 +1092,7 @@ 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 db7b6917d9c5..322491e70e41 100644
> > --- a/fs/locks.c
> > +++ b/fs/locks.c
> > @@ -194,7 +194,7 @@ 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).
> >   *
> > @@ -203,7 +203,7 @@ static DEFINE_HASHTABLE(blocked_hash, BLOCKED_HASH_BITS);
> >   * protected by this lock, we can skip acquiring it iff we already hold the
> >   * flc_lock.
> >   *
> > - * In particular, adding an entry to the fl_block list requires that you hold
> > + * In particular, adding an entry to the fl_blocked list requires that you hold
> >   * both the flc_lock and the blocked_lock_lock (acquired in that order).
> >   * Deleting an entry from the list however only requires the file_lock_lock.
> >   */
> > @@ -302,6 +302,7 @@ 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);
> >  }
> > @@ -341,6 +342,7 @@ 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));
> >  
> > @@ -676,7 +678,7 @@ 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)
> > @@ -692,16 +694,16 @@ 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);
> >  }
> > @@ -725,18 +727,18 @@ 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)
> > @@ -887,7 +889,7 @@ 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;
> >  }
> > @@ -1245,7 +1247,7 @@ 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;
> >  
> > @@ -1332,7 +1334,7 @@ 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
> > @@ -1526,7 +1528,7 @@ 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);
> > @@ -1940,7 +1942,7 @@ 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;
> >  
> > @@ -2212,7 +2214,7 @@ 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;
> >  
> > @@ -2583,7 +2585,7 @@ 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;
> > @@ -2711,7 +2713,7 @@ 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 805bf22898cf..48f7f36c3772 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -1002,10 +1002,11 @@ 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 d1faf3597b9d..0e50f985a390 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)
> > @@ -122,7 +122,7 @@ 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)
> > @@ -134,7 +134,7 @@ 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;
> > @@ -142,9 +142,9 @@ 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)
> > 
> > 
> 
> -- 
> Jeff Layton <jlayton@...nel.org>

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