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    SubjectRe: [PATCH 01/12] fs/locks: rename some lists and pointers.
    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)
    >

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