[PATCH 00/12 v6] fs/locks: avoid thundering-herd wake-ups

[PATCH 00/12 v6] fs/locks: avoid thundering-herd wake-ups

[NeilBrown]

This series has the fixes for the recently reported performance
regressions merged into the patches which caused them.
It also has a couple of little fixes that have been mentioned on the
list, and that Jeff had merged into his copy.

Thanks,
NeilBrown

---

NeilBrown (12):
      fs/locks: rename some lists and pointers.
      fs/locks: split out __locks_wake_up_blocks().
      NFS: use locks_copy_lock() to copy locks.
      gfs2: properly initial file_lock used for unlock.
      ocfs2: properly initial file_lock used for unlock.
      fs/locks: use properly initialized file_lock when unlocking.
      fs/locks: allow a lock request to block other requests.
      fs/locks: always delete_block after waiting.
      fs/locks: change all *_conflict() functions to return bool.
      fs/locks: create a tree of dependent requests.
      fs/locks: merge posix_unblock_lock() and locks_delete_block()
      fs/locks: locks: remove unnecessary white space.


 fs/cifs/file.c                  |    4 
 fs/gfs2/file.c                  |   10 +
 fs/lockd/svclock.c              |    2 
 fs/locks.c                      |  342 +++++++++++++++++++++++++--------------
 fs/nfs/nfs4proc.c               |    6 -
 fs/nfsd/nfs4state.c             |    6 -
 fs/ocfs2/locks.c                |   10 +
 include/linux/fs.h              |   13 +
 include/trace/events/filelock.h |   16 +-
 9 files changed, 252 insertions(+), 157 deletions(-)

--
Signature

[PATCH 12/12] fs/locks: remove unnecessary white space.

[NeilBrown]

 - spaces before tabs,
 - spaces at the end of lines,
 - multiple blank lines,
 - blank lines before EXPORT_SYMBOL,
can all go.

Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/locks.c |   33 ++++++++++++---------------------
 1 file changed, 12 insertions(+), 21 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 75a03a9d666e..b6b43970f461 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -11,11 +11,11 @@
  *
  *  Miscellaneous edits, and a total rewrite of posix_lock_file() code.
  *  Kai Petzke (wpp@marie.physik.tu-berlin.de), 1994
- *  
+ *
  *  Converted file_lock_table to a linked list from an array, which eliminates
  *  the limits on how many active file locks are open.
  *  Chad Page (pageone@netcom.com), November 27, 1994
- * 
+ *
  *  Removed dependency on file descriptors. dup()'ed file descriptors now
  *  get the same locks as the original file descriptors, and a close() on
  *  any file descriptor removes ALL the locks on the file for the current
@@ -41,7 +41,7 @@
  *  with a file pointer (filp). As a result they can be shared by a parent
  *  process and its children after a fork(). They are removed when the last
  *  file descriptor referring to the file pointer is closed (unless explicitly
- *  unlocked). 
+ *  unlocked).
  *
  *  FL_FLOCK locks never deadlock, an existing lock is always removed before
  *  upgrading from shared to exclusive (or vice versa). When this happens
@@ -50,7 +50,7 @@
  *  Andy Walker (andy@lysaker.kvaerner.no), June 09, 1995
  *
  *  Removed some race conditions in flock_lock_file(), marked other possible
- *  races. Just grep for FIXME to see them. 
+ *  races. Just grep for FIXME to see them.
  *  Dmitry Gorodchanin (pgmdsg@ibi.com), February 09, 1996.
  *
  *  Addressed Dmitry's concerns. Deadlock checking no longer recursive.
@@ -399,7 +399,6 @@ void locks_init_lock(struct file_lock *fl)
 	memset(fl, 0, sizeof(struct file_lock));
 	locks_init_lock_heads(fl);
 }
-
 EXPORT_SYMBOL(locks_init_lock);
 
 /*
@@ -439,7 +438,6 @@ void locks_copy_lock(struct file_lock *new, struct file_lock *fl)
 			fl->fl_ops->fl_copy_lock(new, fl);
 	}
 }
-
 EXPORT_SYMBOL(locks_copy_lock);
 
 static void locks_move_blocks(struct file_lock *new, struct file_lock *fl)
@@ -482,7 +480,7 @@ flock_make_lock(struct file *filp, unsigned int cmd, struct file_lock *fl)
 
 	if (type < 0)
 		return ERR_PTR(type);
-	
+
 	if (fl == NULL) {
 		fl = locks_alloc_lock();
 		if (fl == NULL)
@@ -497,7 +495,7 @@ flock_make_lock(struct file *filp, unsigned int cmd, struct file_lock *fl)
 	fl->fl_flags = FL_FLOCK;
 	fl->fl_type = type;
 	fl->fl_end = OFFSET_MAX;
-	
+
 	return fl;
 }
 
@@ -1169,8 +1167,8 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
 			}
 			spin_unlock(&blocked_lock_lock);
 			goto out;
-  		}
-  	}
+		}
+	}
 
 	/* If we're just looking for a conflict, we're done. */
 	error = 0;
@@ -1465,7 +1463,6 @@ int locks_mandatory_area(struct inode *inode, struct file *filp, loff_t start,
 
 	return error;
 }
-
 EXPORT_SYMBOL(locks_mandatory_area);
 #endif /* CONFIG_MANDATORY_FILE_LOCKING */
 
@@ -1667,7 +1664,6 @@ int __break_lease(struct inode *inode, unsigned int mode, unsigned int type)
 	locks_free_lock(new_fl);
 	return error;
 }
-
 EXPORT_SYMBOL(__break_lease);
 
 /**
@@ -1698,7 +1694,6 @@ void lease_get_mtime(struct inode *inode, struct timespec64 *time)
 	if (has_lease)
 		*time = current_time(inode);
 }
-
 EXPORT_SYMBOL(lease_get_mtime);
 
 /**
@@ -1753,8 +1748,8 @@ int fcntl_getlease(struct file *filp)
 
 /**
  * check_conflicting_open - see if the given dentry points to a file that has
- * 			    an existing open that would conflict with the
- * 			    desired lease.
+ *			    an existing open that would conflict with the
+ *			    desired lease.
  * @dentry:	dentry to check
  * @arg:	type of lease that we're trying to acquire
  * @flags:	current lock flags
@@ -1978,7 +1973,7 @@ EXPORT_SYMBOL(generic_setlease);
  * @arg:	type of lease to obtain
  * @lease:	file_lock to use when adding a lease
  * @priv:	private info for lm_setup when adding a lease (may be
- * 		NULL if lm_setup doesn't require it)
+ *		NULL if lm_setup doesn't require it)
  *
  * Call this to establish a lease on the file. The "lease" argument is not
  * used for F_UNLCK requests and may be NULL. For commands that set or alter
@@ -2266,7 +2261,7 @@ int fcntl_getlk(struct file *filp, unsigned int cmd, struct flock *flock)
 	error = vfs_test_lock(filp, fl);
 	if (error)
 		goto out;
- 
+
 	flock->l_type = fl->fl_type;
 	if (fl->fl_type != F_UNLCK) {
 		error = posix_lock_to_flock(flock, fl);
@@ -2614,7 +2609,6 @@ void locks_remove_posix(struct file *filp, fl_owner_t owner)
 		lock.fl_ops->fl_release_private(&lock);
 	trace_locks_remove_posix(inode, &lock, error);
 }
-
 EXPORT_SYMBOL(locks_remove_posix);
 
 /* The i_flctx must be valid when calling into here */
@@ -2700,7 +2694,6 @@ int vfs_cancel_lock(struct file *filp, struct file_lock *fl)
 		return filp->f_op->lock(filp, F_CANCELLK, fl);
 	return 0;
 }
-
 EXPORT_SYMBOL_GPL(vfs_cancel_lock);
 
 #ifdef CONFIG_PROC_FS
@@ -2900,7 +2893,6 @@ static int __init filelock_init(void)
 	filelock_cache = kmem_cache_create("file_lock_cache",
 			sizeof(struct file_lock), 0, SLAB_PANIC, NULL);
 
-
 	for_each_possible_cpu(i) {
 		struct file_lock_list_struct *fll = per_cpu_ptr(&file_lock_list, i);
 
@@ -2910,5 +2902,4 @@ static int __init filelock_init(void)
 
 	return 0;
 }
-
 core_initcall(filelock_init);

[PATCH 06/12] fs/locks: use properly initialized file_lock when unlocking.

[NeilBrown]

Both locks_remove_posix() and locks_remove_flock() use a
struct file_lock without calling locks_init_lock() on it.
This means the various list_heads are not initialized, which
will become a problem with a later patch.

So change them both to initialize properly.  For flock locks,
this involves using flock_make_lock(), and changing it to
allow a file_lock to be passed in, so memory allocation isn't
always needed.

Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/locks.c |   28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 6adb22a21a92..492d970c67d7 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -418,17 +418,20 @@ static inline int flock_translate_cmd(int cmd) {
 
 /* Fill in a file_lock structure with an appropriate FLOCK lock. */
 static struct file_lock *
-flock_make_lock(struct file *filp, unsigned int cmd)
+flock_make_lock(struct file *filp, unsigned int cmd, struct file_lock *fl)
 {
-	struct file_lock *fl;
 	int type = flock_translate_cmd(cmd);
 
 	if (type < 0)
 		return ERR_PTR(type);
 	
-	fl = locks_alloc_lock();
-	if (fl == NULL)
-		return ERR_PTR(-ENOMEM);
+	if (fl == NULL) {
+		fl = locks_alloc_lock();
+		if (fl == NULL)
+			return ERR_PTR(-ENOMEM);
+	} else {
+		locks_init_lock(fl);
+	}
 
 	fl->fl_file = filp;
 	fl->fl_owner = filp;
@@ -2009,7 +2012,7 @@ SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
 	    !(f.file->f_mode & (FMODE_READ|FMODE_WRITE)))
 		goto out_putf;
 
-	lock = flock_make_lock(f.file, cmd);
+	lock = flock_make_lock(f.file, cmd, NULL);
 	if (IS_ERR(lock)) {
 		error = PTR_ERR(lock);
 		goto out_putf;
@@ -2484,6 +2487,7 @@ void locks_remove_posix(struct file *filp, fl_owner_t owner)
 	if (!ctx || list_empty(&ctx->flc_posix))
 		return;
 
+	locks_init_lock(&lock);
 	lock.fl_type = F_UNLCK;
 	lock.fl_flags = FL_POSIX | FL_CLOSE;
 	lock.fl_start = 0;
@@ -2507,19 +2511,15 @@ EXPORT_SYMBOL(locks_remove_posix);
 static void
 locks_remove_flock(struct file *filp, struct file_lock_context *flctx)
 {
-	struct file_lock fl = {
-		.fl_owner = filp,
-		.fl_pid = current->tgid,
-		.fl_file = filp,
-		.fl_flags = FL_FLOCK | FL_CLOSE,
-		.fl_type = F_UNLCK,
-		.fl_end = OFFSET_MAX,
-	};
+	struct file_lock fl;
 	struct inode *inode = locks_inode(filp);
 
 	if (list_empty(&flctx->flc_flock))
 		return;
 
+	flock_make_lock(filp, LOCK_UN, &fl);
+	fl.fl_flags |= FL_CLOSE;
+
 	if (filp->f_op->flock)
 		filp->f_op->flock(filp, F_SETLKW, &fl);
 	else

[PATCH 05/12] ocfs2: properly initial file_lock used for unlock.

[NeilBrown]

Rather than assuming all-zeros is sufficient, use the available API to
initialize the file_lock structure use for unlock.  VFS-level changes
will soon make it important that the list_heads in file_lock are
always properly initialized.

Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/ocfs2/locks.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/ocfs2/locks.c b/fs/ocfs2/locks.c
index d56f0079b858..b11acd34001a 100644
--- a/fs/ocfs2/locks.c
+++ b/fs/ocfs2/locks.c
@@ -52,6 +52,7 @@ static int ocfs2_do_flock(struct file *file, struct inode *inode,
 	if (lockres->l_flags & OCFS2_LOCK_ATTACHED &&
 	    lockres->l_level > LKM_NLMODE) {
 		int old_level = 0;
+		struct file_lock request;
 
 		if (lockres->l_level == LKM_EXMODE)
 			old_level = 1;
@@ -66,11 +67,10 @@ static int ocfs2_do_flock(struct file *file, struct inode *inode,
 		 * level.
 		 */
 
-		locks_lock_file_wait(file,
-				&(struct file_lock) {
-					.fl_type = F_UNLCK,
-					.fl_flags = FL_FLOCK
-				});
+		locks_init_lock(&request);
+		request.fl_type = F_UNLCK;
+		request.fl_flags = FL_FLOCK;
+		locks_lock_file_wait(file, &request);
 
 		ocfs2_file_unlock(file);
 	}

[PATCH 10/12] fs/locks: create a tree of dependent requests.

[NeilBrown]

When we find an existing lock which conflicts with a request,
and the request wants to wait, we currently add the request
to a list.  When the lock is removed, the whole list is woken.
This can cause the thundering-herd problem.
To reduce the problem, we make use of the (new) fact that
a pending request can itself have a list of blocked requests.
When we find a conflict, we look through the existing blocked requests.
If any one of them blocks the new request, the new request is attached
below that request, otherwise it is added to the list of blocked
requests, which are now known to be mutually non-conflicting.

This way, when the lock is released, only a set of non-conflicting
locks will be woken, the rest can stay asleep.
If the lock request cannot be granted and the request needs to be
requeued, all the other requests it blocks will then be woken

To make this more concrete:

  If you have a many-core machine, and have many threads all wanting to
  briefly lock a give file (udev is known to do this), you can get quite
  poor performance.

  When one thread releases a lock, it wakes up all other threads that
  are waiting (classic thundering-herd) - one will get the lock and the
  others go to sleep.
  When you have few cores, this is not very noticeable: by the time the
  4th or 5th thread gets enough CPU time to try to claim the lock, the
  earlier threads have claimed it, done what was needed, and released.
  So with few cores, many of the threads don't end up contending.
  With 50+ cores, lost of threads can get the CPU at the same time,
  and the contention can easily be measured.

  This patchset creates a tree of pending lock requests in which siblings
  don't conflict and each lock request does conflict with its parent.
  When a lock is released, only requests which don't conflict with each
  other a woken.

  Testing shows that lock-acquisitions-per-second is now fairly stable
  even as the number of contending process goes to 1000.  Without this
  patch, locks-per-second drops off steeply after a few 10s of
  processes.

  There is a small cost to this extra complexity.
  At 20 processes running a particular test on 72 cores, the lock
  acquisitions per second drops from 1.8 million to 1.4 million with
  this patch.  For 100 processes, this patch still provides 1.4 million
  while without this patch there are about 700,000.


Reported-and-tested-by: Martin Wilck <mwilck@suse.de>
Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/locks.c |   69 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 63 insertions(+), 6 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 91fc29912151..7a55d6feb12a 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -112,6 +112,46 @@
  *  Leases and LOCK_MAND
  *  Matthew Wilcox <willy@debian.org>, June, 2000.
  *  Stephen Rothwell <sfr@canb.auug.org.au>, June, 2000.
+ *
+ * Locking conflicts and dependencies:
+ * If multiple threads attempt to lock the same byte (or flock the same file)
+ * only one can be granted the lock, and other must wait their turn.
+ * The first lock has been "applied" or "granted", the others are "waiting"
+ * and are "blocked" by the "applied" lock..
+ *
+ * Waiting and applied locks are all kept in trees whose properties are:
+ *
+ *	- the root of a tree may be an applied or waiting lock.
+ *	- every other node in the tree is a waiting lock that
+ *	  conflicts with every ancestor of that node.
+ *
+ * Every such tree begins life as a waiting singleton which obviously
+ * satisfies the above properties.
+ *
+ * The only ways we modify trees preserve these properties:
+ *
+ *	1. We may add a new leaf node, but only after first verifying that it
+ *	   conflicts with all of its ancestors.
+ *	2. We may remove the root of a tree, creating a new singleton
+ *	   tree from the root and N new trees rooted in the immediate
+ *	   children.
+ *	3. If the root of a tree is not currently an applied lock, we may
+ *	   apply it (if possible).
+ *	4. We may upgrade the root of the tree (either extend its range,
+ *	   or upgrade its entire range from read to write).
+ *
+ * When an applied lock is modified in a way that reduces or downgrades any
+ * part of its range, we remove all its children (2 above).  This particularly
+ * happens when a lock is unlocked.
+ *
+ * For each of those child trees we "wake up" the thread which is
+ * waiting for the lock so it can continue handling as follows: if the
+ * root of the tree applies, we do so (3).  If it doesn't, it must
+ * conflict with some applied lock.  We remove (wake up) all of its children
+ * (2), and add it is a new leaf to the tree rooted in the applied
+ * lock (1).  We then repeat the process recursively with those
+ * children.
+ *
  */
 
 #include <linux/capability.h>
@@ -740,11 +780,25 @@ static void locks_delete_block(struct file_lock *waiter)
  * 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_blocked_requests list is empty.
+ *
+ * Rather than just adding to the list, we check for conflicts with any existing
+ * waiters, and add beneath any waiter that blocks the new waiter.
+ * Thus wakeups don't happen until needed.
  */
 static void __locks_insert_block(struct file_lock *blocker,
-					struct file_lock *waiter)
+				 struct file_lock *waiter,
+				 bool conflict(struct file_lock *,
+					       struct file_lock *))
 {
+	struct file_lock *fl;
 	BUG_ON(!list_empty(&waiter->fl_blocked_member));
+
+new_blocker:
+	list_for_each_entry(fl, &blocker->fl_blocked_requests, fl_blocked_member)
+		if (conflict(fl, waiter)) {
+			blocker =  fl;
+			goto new_blocker;
+		}
 	waiter->fl_blocker = blocker;
 	list_add_tail(&waiter->fl_blocked_member, &blocker->fl_blocked_requests);
 	if (IS_POSIX(blocker) && !IS_OFDLCK(blocker))
@@ -759,10 +813,12 @@ static void __locks_insert_block(struct file_lock *blocker,
 
 /* Must be called with flc_lock held. */
 static void locks_insert_block(struct file_lock *blocker,
-					struct file_lock *waiter)
+			       struct file_lock *waiter,
+			       bool conflict(struct file_lock *,
+					     struct file_lock *))
 {
 	spin_lock(&blocked_lock_lock);
-	__locks_insert_block(blocker, waiter);
+	__locks_insert_block(blocker, waiter, conflict);
 	spin_unlock(&blocked_lock_lock);
 }
 
@@ -1021,7 +1077,7 @@ static int flock_lock_inode(struct inode *inode, struct file_lock *request)
 		if (!(request->fl_flags & FL_SLEEP))
 			goto out;
 		error = FILE_LOCK_DEFERRED;
-		locks_insert_block(fl, request);
+		locks_insert_block(fl, request, flock_locks_conflict);
 		goto out;
 	}
 	if (request->fl_flags & FL_ACCESS)
@@ -1096,7 +1152,8 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
 			spin_lock(&blocked_lock_lock);
 			if (likely(!posix_locks_deadlock(request, fl))) {
 				error = FILE_LOCK_DEFERRED;
-				__locks_insert_block(fl, request);
+				__locks_insert_block(fl, request,
+						     posix_locks_conflict);
 			}
 			spin_unlock(&blocked_lock_lock);
 			goto out;
@@ -1567,7 +1624,7 @@ int __break_lease(struct inode *inode, unsigned int mode, unsigned int type)
 		break_time -= jiffies;
 	if (break_time == 0)
 		break_time++;
-	locks_insert_block(fl, new_fl);
+	locks_insert_block(fl, new_fl, leases_conflict);
 	trace_break_lease_block(inode, new_fl);
 	spin_unlock(&ctx->flc_lock);
 	percpu_up_read_preempt_enable(&file_rwsem);

[PATCH 03/12] NFS: use locks_copy_lock() to copy locks.

[NeilBrown]

Using memcpy() to copy lock requests leaves the various
list_head in an inconsistent state.
As we will soon attach a list of conflicting request to
another pending request, we need these lists to be consistent.
So change NFS to use locks_init_lock/locks_copy_lock instead
of memcpy.

Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/nfs/nfs4proc.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 867457d6dfbe..0ba2b0fb8ff3 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -6311,7 +6311,8 @@ static struct nfs4_unlockdata *nfs4_alloc_unlockdata(struct file_lock *fl,
 	/* Ensure we don't close file until we're done freeing locks! */
 	p->ctx = get_nfs_open_context(ctx);
 	p->l_ctx = nfs_get_lock_context(ctx);
-	memcpy(&p->fl, fl, sizeof(p->fl));
+	locks_init_lock(&p->fl);
+	locks_copy_lock(&p->fl, fl);
 	p->server = NFS_SERVER(inode);
 	return p;
 }
@@ -6533,7 +6534,8 @@ static struct nfs4_lockdata *nfs4_alloc_lockdata(struct file_lock *fl,
 	p->server = server;
 	refcount_inc(&lsp->ls_count);
 	p->ctx = get_nfs_open_context(ctx);
-	memcpy(&p->fl, fl, sizeof(p->fl));
+	locks_init_lock(&p->fl);
+	locks_copy_lock(&p->fl, fl);
 	return p;
 out_free_seqid:
 	nfs_free_seqid(p->arg.open_seqid);

[PATCH 07/12] fs/locks: allow a lock request to block other requests.

[NeilBrown]

Currently, a lock can block pending requests, but all pending
requests are equal.  If lots of pending requests are
mutually exclusive, this means they will all be woken up
and all but one will fail.  This can hurt performance.

So we will allow pending requests to block other requests.
Only the first request will be woken, and it will wake the others.

This patch doesn't implement this fully, but prepares the way.

- It acknowledges that a request might be blocking other requests,
  and when the request is converted to a lock, those blocked
  requests are moved across.
- When a request is requeued or discarded, all blocked requests are
  woken.
- When deadlock-detection looks for the lock which blocks a
  given request, we follow the chain of ->fl_blocker all
  the way to the top.

Tested-by: kernel test robot <rong.a.chen@intel.com>
Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/locks.c |   43 +++++++++++++++++++++++++++++++++++++------
 1 file changed, 37 insertions(+), 6 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 492d970c67d7..1260c265ba62 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -402,6 +402,24 @@ void locks_copy_lock(struct file_lock *new, struct file_lock *fl)
 
 EXPORT_SYMBOL(locks_copy_lock);
 
+static void locks_move_blocks(struct file_lock *new, struct file_lock *fl)
+{
+	struct file_lock *f;
+
+	/*
+	 * As ctx->flc_lock is held, new requests cannot be added to
+	 * ->fl_blocked_requests, so we don't need a lock to check if it
+	 * is empty.
+	 */
+	if (list_empty(&fl->fl_blocked_requests))
+		return;
+	spin_lock(&blocked_lock_lock);
+	list_splice_init(&fl->fl_blocked_requests, &new->fl_blocked_requests);
+	list_for_each_entry(f, &fl->fl_blocked_requests, fl_blocked_member)
+		f->fl_blocker = new;
+	spin_unlock(&blocked_lock_lock);
+}
+
 static inline int flock_translate_cmd(int cmd) {
 	if (cmd & LOCK_MAND)
 		return cmd & (LOCK_MAND | LOCK_RW);
@@ -693,6 +711,7 @@ static void __locks_wake_up_blocks(struct file_lock *blocker)
 static void locks_delete_block(struct file_lock *waiter)
 {
 	spin_lock(&blocked_lock_lock);
+	__locks_wake_up_blocks(waiter);
 	__locks_delete_block(waiter);
 	spin_unlock(&blocked_lock_lock);
 }
@@ -716,6 +735,12 @@ static void __locks_insert_block(struct file_lock *blocker,
 	list_add_tail(&waiter->fl_blocked_member, &blocker->fl_blocked_requests);
 	if (IS_POSIX(blocker) && !IS_OFDLCK(blocker))
 		locks_insert_global_blocked(waiter);
+
+	/* The requests in waiter->fl_blocked are known to conflict with
+	 * waiter, but might not conflict with blocker, or the requests
+	 * and lock which block it.  So they all need to be woken.
+	 */
+	__locks_wake_up_blocks(waiter);
 }
 
 /* Must be called with flc_lock held. */
@@ -888,8 +913,11 @@ static struct file_lock *what_owner_is_waiting_for(struct file_lock *block_fl)
 	struct file_lock *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_blocker;
+		if (posix_same_owner(fl, block_fl)) {
+			while (fl->fl_blocker)
+				fl = fl->fl_blocker;
+			return fl;
+		}
 	}
 	return NULL;
 }
@@ -982,6 +1010,7 @@ static int flock_lock_inode(struct inode *inode, struct file_lock *request)
 	if (request->fl_flags & FL_ACCESS)
 		goto out;
 	locks_copy_lock(new_fl, request);
+	locks_move_blocks(new_fl, request);
 	locks_insert_lock_ctx(new_fl, &ctx->flc_flock);
 	new_fl = NULL;
 	error = 0;
@@ -1175,6 +1204,7 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
 			goto out;
 		}
 		locks_copy_lock(new_fl, request);
+		locks_move_blocks(new_fl, request);
 		locks_insert_lock_ctx(new_fl, &fl->fl_list);
 		fl = new_fl;
 		new_fl = NULL;
@@ -2586,13 +2616,14 @@ void locks_remove_file(struct file *filp)
 int
 posix_unblock_lock(struct file_lock *waiter)
 {
-	int status = 0;
+	int status = -ENOENT;
 
 	spin_lock(&blocked_lock_lock);
-	if (waiter->fl_blocker)
+	if (waiter->fl_blocker) {
+		__locks_wake_up_blocks(waiter);
 		__locks_delete_block(waiter);
-	else
-		status = -ENOENT;
+		status = 0;
+	}
 	spin_unlock(&blocked_lock_lock);
 	return status;
 }

[PATCH 09/12] fs/locks: change all *_conflict() functions to return bool.

[NeilBrown]

posix_locks_conflict() and flock_locks_conflict() both return int.
leases_conflict() returns bool.

This inconsistency will cause problems for the next patch if not
fixed.

So change posix_locks_conflict() and flock_locks_conflict() to return
bool.
Also change the locks_conflict() helper.

And convert some
   return (foo);
to
   return foo;

Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/locks.c |   27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 2814662ecfe6..91fc29912151 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -816,47 +816,50 @@ locks_delete_lock_ctx(struct file_lock *fl, struct list_head *dispose)
 /* Determine if lock sys_fl blocks lock caller_fl. Common functionality
  * checks for shared/exclusive status of overlapping locks.
  */
-static int locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
+static bool locks_conflict(struct file_lock *caller_fl,
+			   struct file_lock *sys_fl)
 {
 	if (sys_fl->fl_type == F_WRLCK)
-		return 1;
+		return true;
 	if (caller_fl->fl_type == F_WRLCK)
-		return 1;
-	return 0;
+		return true;
+	return false;
 }
 
 /* Determine if lock sys_fl blocks lock caller_fl. POSIX specific
  * checking before calling the locks_conflict().
  */
-static int posix_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
+static bool posix_locks_conflict(struct file_lock *caller_fl,
+				 struct file_lock *sys_fl)
 {
 	/* POSIX locks owned by the same process do not conflict with
 	 * each other.
 	 */
 	if (posix_same_owner(caller_fl, sys_fl))
-		return (0);
+		return false;
 
 	/* Check whether they overlap */
 	if (!locks_overlap(caller_fl, sys_fl))
-		return 0;
+		return false;
 
-	return (locks_conflict(caller_fl, sys_fl));
+	return locks_conflict(caller_fl, sys_fl);
 }
 
 /* Determine if lock sys_fl blocks lock caller_fl. FLOCK specific
  * checking before calling the locks_conflict().
  */
-static int flock_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
+static bool flock_locks_conflict(struct file_lock *caller_fl,
+				 struct file_lock *sys_fl)
 {
 	/* FLOCK locks referring to the same filp do not conflict with
 	 * each other.
 	 */
 	if (caller_fl->fl_file == sys_fl->fl_file)
-		return (0);
+		return false;
 	if ((caller_fl->fl_type & LOCK_MAND) || (sys_fl->fl_type & LOCK_MAND))
-		return 0;
+		return false;
 
-	return (locks_conflict(caller_fl, sys_fl));
+	return locks_conflict(caller_fl, sys_fl);
 }
 
 void

[PATCH 04/12] gfs2: properly initial file_lock used for unlock.

[NeilBrown]

Rather than assuming all-zeros is sufficient, use the available API to
initialize the file_lock structure use for unlock.  VFS-level changes
will soon make it important that the list_heads in file_lock are
always properly initialized.

Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/gfs2/file.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index 45a17b770d97..a2dea5bc0427 100644
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -1199,13 +1199,13 @@ static int do_flock(struct file *file, int cmd, struct file_lock *fl)
 	mutex_lock(&fp->f_fl_mutex);
 
 	if (gfs2_holder_initialized(fl_gh)) {
+		struct file_lock request;
 		if (fl_gh->gh_state == state)
 			goto out;
-		locks_lock_file_wait(file,
-				     &(struct file_lock) {
-					     .fl_type = F_UNLCK,
-					     .fl_flags = FL_FLOCK
-				     });
+		locks_init_lock(&request);
+		request.fl_type = F_UNLCK;
+		request.fl_flags = FL_FLOCK;
+		locks_lock_file_wait(file, &request);
 		gfs2_glock_dq(fl_gh);
 		gfs2_holder_reinit(state, flags, fl_gh);
 	} else {

[PATCH 08/12] fs/locks: always delete_block after waiting.

[NeilBrown]

Now that requests can block other requests, we
need to be careful to always clean up those blocked
requests.
Any time that we wait for a request, we might have
other requests attached, and when we stop waiting,
we must clean them up.
If the lock was granted, the requests might have been
moved to the new lock, though when merged with a
pre-exiting lock, this might not happen.
In all cases we don't want blocked locks to remain
attached, so we remove them to be safe.

Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
Tested-by: syzbot+a4a3d526b4157113ec6a@syzkaller.appspotmail.com
Tested-by: kernel test robot <rong.a.chen@intel.com>
---
 fs/locks.c |   40 ++++++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 1260c265ba62..2814662ecfe6 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -710,6 +710,20 @@ static void __locks_wake_up_blocks(struct file_lock *blocker)
 
 static void locks_delete_block(struct file_lock *waiter)
 {
+	/*
+	 * If fl_blocker is NULL, it won't be set again as this thread
+	 * "owns" the lock and is the only one that might try to claim
+	 * the lock.  So it is safe to test fl_blocker locklessly.
+	 * Also if fl_blocker is NULL, this waiter is not listed on
+	 * fl_blocked_requests for some lock, so no other request can
+	 * be added to the list of fl_blocked_requests for this
+	 * request.  So if fl_blocker is NULL, it is safe to
+	 * locklessly check if fl_blocked_requests is empty.  If both
+	 * of these checks succeed, there is no need to take the lock.
+	 */
+	if (waiter->fl_blocker == NULL &&
+	    list_empty(&waiter->fl_blocked_requests))
+		return status;
 	spin_lock(&blocked_lock_lock);
 	__locks_wake_up_blocks(waiter);
 	__locks_delete_block(waiter);
@@ -1279,12 +1293,10 @@ static int posix_lock_inode_wait(struct inode *inode, struct file_lock *fl)
 		if (error != FILE_LOCK_DEFERRED)
 			break;
 		error = wait_event_interruptible(fl->fl_wait, !fl->fl_blocker);
-		if (!error)
-			continue;
-
-		locks_delete_block(fl);
-		break;
+		if (error)
+			break;
 	}
+	locks_delete_block(fl);
 	return error;
 }
 
@@ -1375,9 +1387,9 @@ int locks_mandatory_area(struct inode *inode, struct file *filp, loff_t start,
 				continue;
 		}
 
-		locks_delete_block(&fl);
 		break;
 	}
+	locks_delete_block(&fl);
 
 	return error;
 }
@@ -1973,12 +1985,10 @@ static int flock_lock_inode_wait(struct inode *inode, struct file_lock *fl)
 		if (error != FILE_LOCK_DEFERRED)
 			break;
 		error = wait_event_interruptible(fl->fl_wait, !fl->fl_blocker);
-		if (!error)
-			continue;
-
-		locks_delete_block(fl);
-		break;
+		if (error)
+			break;
 	}
+	locks_delete_block(fl);
 	return error;
 }
 
@@ -2252,12 +2262,10 @@ static int do_lock_file_wait(struct file *filp, unsigned int cmd,
 		if (error != FILE_LOCK_DEFERRED)
 			break;
 		error = wait_event_interruptible(fl->fl_wait, !fl->fl_blocker);
-		if (!error)
-			continue;
-
-		locks_delete_block(fl);
-		break;
+		if (error)
+			break;
 	}
+	locks_delete_block(fl);
 
 	return error;
 }

[PATCH 02/12] fs/locks: split out __locks_wake_up_blocks().

[NeilBrown]

This functionality will be useful in future patches, so
split it out from locks_wake_up_blocks().

Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/locks.c |   27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index c6df0c8b3d13..6adb22a21a92 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -672,6 +672,21 @@ static void __locks_delete_block(struct file_lock *waiter)
 	waiter->fl_blocker = NULL;
 }
 
+static void __locks_wake_up_blocks(struct file_lock *blocker)
+{
+	while (!list_empty(&blocker->fl_blocked_requests)) {
+		struct file_lock *waiter;
+
+		waiter = list_first_entry(&blocker->fl_blocked_requests,
+					  struct file_lock, fl_blocked_member);
+		__locks_delete_block(waiter);
+		if (waiter->fl_lmops && waiter->fl_lmops->lm_notify)
+			waiter->fl_lmops->lm_notify(waiter);
+		else
+			wake_up(&waiter->fl_wait);
+	}
+}
+
 static void locks_delete_block(struct file_lock *waiter)
 {
 	spin_lock(&blocked_lock_lock);
@@ -727,17 +742,7 @@ static void locks_wake_up_blocks(struct file_lock *blocker)
 		return;
 
 	spin_lock(&blocked_lock_lock);
-	while (!list_empty(&blocker->fl_blocked_requests)) {
-		struct file_lock *waiter;
-
-		waiter = list_first_entry(&blocker->fl_blocked_requests,
-				struct file_lock, fl_blocked_member);
-		__locks_delete_block(waiter);
-		if (waiter->fl_lmops && waiter->fl_lmops->lm_notify)
-			waiter->fl_lmops->lm_notify(waiter);
-		else
-			wake_up(&waiter->fl_wait);
-	}
+	__locks_wake_up_blocks(blocker);
 	spin_unlock(&blocked_lock_lock);
 }
 

[PATCH 11/12] fs/locks: merge posix_unblock_lock() and locks_delete_block()

[NeilBrown]

posix_unblock_lock() is not specific to posix locks, and behaves
nearly identically to locks_delete_block() - the former returning a
status while the later doesn't.

So discard posix_unblock_lock() and use locks_delete_block() instead,
after giving that function an appropriate return value.

Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/cifs/file.c      |    2 +-
 fs/lockd/svclock.c  |    2 +-
 fs/locks.c          |   36 +++++++++++++-----------------------
 fs/nfsd/nfs4state.c |    6 +++---
 include/linux/fs.h  |    4 ++--
 5 files changed, 20 insertions(+), 30 deletions(-)

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index d7ed895e05d1..94c3575e850c 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1106,7 +1106,7 @@ cifs_posix_lock_set(struct file *file, struct file_lock *flock)
 		rc = wait_event_interruptible(flock->fl_wait, !flock->fl_blocker);
 		if (!rc)
 			goto try_again;
-		posix_unblock_lock(flock);
+		locks_delete_block(flock);
 	}
 	return rc;
 }
diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
index 74330daeab71..ea719cdd6a36 100644
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -276,7 +276,7 @@ static int nlmsvc_unlink_block(struct nlm_block *block)
 	dprintk("lockd: unlinking block %p...\n", block);
 
 	/* Remove block from list */
-	status = posix_unblock_lock(&block->b_call->a_args.lock.fl);
+	status = locks_delete_block(&block->b_call->a_args.lock.fl);
 	nlmsvc_remove_block(block);
 	return status;
 }
diff --git a/fs/locks.c b/fs/locks.c
index 7a55d6feb12a..75a03a9d666e 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -748,8 +748,16 @@ static void __locks_wake_up_blocks(struct file_lock *blocker)
 	}
 }
 
-static void locks_delete_block(struct file_lock *waiter)
+/**
+ *	locks_delete_lock - stop waiting for a file lock
+ *	@waiter: the lock which was waiting
+ *
+ *	lockd/nfsd need to disconnect the lock while working on it.
+ */
+int locks_delete_block(struct file_lock *waiter)
 {
+	int status = -ENOENT;
+
 	/*
 	 * If fl_blocker is NULL, it won't be set again as this thread
 	 * "owns" the lock and is the only one that might try to claim
@@ -765,10 +773,14 @@ static void locks_delete_block(struct file_lock *waiter)
 	    list_empty(&waiter->fl_blocked_requests))
 		return status;
 	spin_lock(&blocked_lock_lock);
+	if (waiter->fl_blocker)
+		status = 0;
 	__locks_wake_up_blocks(waiter);
 	__locks_delete_block(waiter);
 	spin_unlock(&blocked_lock_lock);
+	return status;
 }
+EXPORT_SYMBOL(locks_delete_block);
 
 /* Insert waiter into blocker's block list.
  * We use a circular list so that processes can be easily woken up in
@@ -2675,28 +2687,6 @@ void locks_remove_file(struct file *filp)
 	spin_unlock(&ctx->flc_lock);
 }
 
-/**
- *	posix_unblock_lock - stop waiting for a file lock
- *	@waiter: the lock which was waiting
- *
- *	lockd needs to block waiting for locks.
- */
-int
-posix_unblock_lock(struct file_lock *waiter)
-{
-	int status = -ENOENT;
-
-	spin_lock(&blocked_lock_lock);
-	if (waiter->fl_blocker) {
-		__locks_wake_up_blocks(waiter);
-		__locks_delete_block(waiter);
-		status = 0;
-	}
-	spin_unlock(&blocked_lock_lock);
-	return status;
-}
-EXPORT_SYMBOL(posix_unblock_lock);
-
 /**
  * vfs_cancel_lock - file byte range unblock lock
  * @filp: The file to apply the unblock to
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index f093fbe47133..a334828723fa 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -238,7 +238,7 @@ find_blocked_lock(struct nfs4_lockowner *lo, struct knfsd_fh *fh,
 	}
 	spin_unlock(&nn->blocked_locks_lock);
 	if (found)
-		posix_unblock_lock(&found->nbl_lock);
+		locks_delete_block(&found->nbl_lock);
 	return found;
 }
 
@@ -293,7 +293,7 @@ remove_blocked_locks(struct nfs4_lockowner *lo)
 		nbl = list_first_entry(&reaplist, struct nfsd4_blocked_lock,
 					nbl_lru);
 		list_del_init(&nbl->nbl_lru);
-		posix_unblock_lock(&nbl->nbl_lock);
+		locks_delete_block(&nbl->nbl_lock);
 		free_blocked_lock(nbl);
 	}
 }
@@ -4863,7 +4863,7 @@ nfs4_laundromat(struct nfsd_net *nn)
 		nbl = list_first_entry(&reaplist,
 					struct nfsd4_blocked_lock, nbl_lru);
 		list_del_init(&nbl->nbl_lru);
-		posix_unblock_lock(&nbl->nbl_lock);
+		locks_delete_block(&nbl->nbl_lock);
 		free_blocked_lock(nbl);
 	}
 out:
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 16df3a7df378..26a8607b3c3c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1124,7 +1124,7 @@ extern void locks_remove_file(struct file *);
 extern void locks_release_private(struct file_lock *);
 extern void posix_test_lock(struct file *, struct file_lock *);
 extern int posix_lock_file(struct file *, struct file_lock *, struct file_lock *);
-extern int posix_unblock_lock(struct file_lock *);
+extern int locks_delete_block(struct file_lock *);
 extern int vfs_test_lock(struct file *, struct file_lock *);
 extern int vfs_lock_file(struct file *, unsigned int, struct file_lock *, struct file_lock *);
 extern int vfs_cancel_lock(struct file *filp, struct file_lock *fl);
@@ -1214,7 +1214,7 @@ static inline int posix_lock_file(struct file *filp, struct file_lock *fl,
 	return -ENOLCK;
 }
 
-static inline int posix_unblock_lock(struct file_lock *waiter)
+static inline int locks_delete_block(struct file_lock *waiter)
 {
 	return -ENOENT;
 }

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

[NeilBrown]

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_requests is the head of a list of blocked requests
fl_blocked_member is a node in a member of that list.

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>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/cifs/file.c                  |    2 +
 fs/locks.c                      |   59 ++++++++++++++++++++-------------------
 include/linux/fs.h              |    9 +++++-
 include/trace/events/filelock.h |   16 +++++------
 4 files changed, 47 insertions(+), 39 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..c6df0c8b3d13 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -189,9 +189,9 @@ 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
- * pointer for file_lock structures that are acting as lock requests (in
- * contrast to those that are acting as records of acquired locks).
+ * In addition, it also protects the fl->fl_blocked_requests 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).
  *
  * Note that when we acquire this lock in order to change the above fields,
  * we often hold the flc_lock as well. In certain cases, when reading the fields
@@ -293,7 +293,8 @@ 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_block);
+	INIT_LIST_HEAD(&fl->fl_blocked_requests);
+	INIT_LIST_HEAD(&fl->fl_blocked_member);
 	init_waitqueue_head(&fl->fl_wait);
 }
 
@@ -332,7 +333,8 @@ 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_block));
+	BUG_ON(!list_empty(&fl->fl_blocked_requests));
+	BUG_ON(!list_empty(&fl->fl_blocked_member));
 	BUG_ON(!hlist_unhashed(&fl->fl_link));
 
 	locks_release_private(fl);
@@ -666,8 +668,8 @@ static void locks_delete_global_blocked(struct file_lock *waiter)
 static void __locks_delete_block(struct file_lock *waiter)
 {
 	locks_delete_global_blocked(waiter);
-	list_del_init(&waiter->fl_block);
-	waiter->fl_next = NULL;
+	list_del_init(&waiter->fl_blocked_member);
+	waiter->fl_blocker = NULL;
 }
 
 static void locks_delete_block(struct file_lock *waiter)
@@ -683,16 +685,17 @@ 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
- * 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.
+ * fl_blocked_requests 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_blocked_requests 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);
+	BUG_ON(!list_empty(&waiter->fl_blocked_member));
+	waiter->fl_blocker = blocker;
+	list_add_tail(&waiter->fl_blocked_member, &blocker->fl_blocked_requests);
 	if (IS_POSIX(blocker) && !IS_OFDLCK(blocker))
 		locks_insert_global_blocked(waiter);
 }
@@ -716,19 +719,19 @@ 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
-	 * list does not require the flc_lock, so we must recheck list_empty()
-	 * after acquiring the blocked_lock_lock.
+	 * the flc_lock is always held here. Note that removal from the
+	 * fl_blocked_requests 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_requests))
 		return;
 
 	spin_lock(&blocked_lock_lock);
-	while (!list_empty(&blocker->fl_block)) {
+	while (!list_empty(&blocker->fl_blocked_requests)) {
 		struct file_lock *waiter;
 
-		waiter = list_first_entry(&blocker->fl_block,
-				struct file_lock, fl_block);
+		waiter = list_first_entry(&blocker->fl_blocked_requests,
+				struct file_lock, fl_blocked_member);
 		__locks_delete_block(waiter);
 		if (waiter->fl_lmops && waiter->fl_lmops->lm_notify)
 			waiter->fl_lmops->lm_notify(waiter);
@@ -878,7 +881,7 @@ 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 +1240,7 @@ 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 +1327,7 @@ 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 +1521,7 @@ 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 +1934,7 @@ 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 +2213,7 @@ 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 +2584,7 @@ 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 +2710,7 @@ 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_requests, fl_blocked_member)
 		lock_get_status(f, bfl, iter->li_pos, " ->");
 
 	return 0;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c95c0807471f..16df3a7df378 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1044,10 +1044,15 @@ 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_requests;	/* list of requests with
+						 * ->fl_blocker pointing here
+						 */
+	struct list_head fl_blocked_member;	/* node in
+						 * ->fl_blocker->fl_blocked_requests
+						 */
 	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)

Re: [PATCH 00/12 v6] fs/locks: avoid thundering-herd wake-ups

[Jeff Layton]

On Fri, 2018-11-30 at 10:04 +1100, NeilBrown wrote:
> This series has the fixes for the recently reported performance
> regressions merged into the patches which caused them.
> It also has a couple of little fixes that have been mentioned on the
> list, and that Jeff had merged into his copy.
> 
> Thanks,
> NeilBrown
> 
> ---
> 
> NeilBrown (12):
>       fs/locks: rename some lists and pointers.
>       fs/locks: split out __locks_wake_up_blocks().
>       NFS: use locks_copy_lock() to copy locks.
>       gfs2: properly initial file_lock used for unlock.
>       ocfs2: properly initial file_lock used for unlock.
>       fs/locks: use properly initialized file_lock when unlocking.
>       fs/locks: allow a lock request to block other requests.
>       fs/locks: always delete_block after waiting.
>       fs/locks: change all *_conflict() functions to return bool.
>       fs/locks: create a tree of dependent requests.
>       fs/locks: merge posix_unblock_lock() and locks_delete_block()
>       fs/locks: locks: remove unnecessary white space.
> 
> 
>  fs/cifs/file.c                  |    4 
>  fs/gfs2/file.c                  |   10 +
>  fs/lockd/svclock.c              |    2 
>  fs/locks.c                      |  342 +++++++++++++++++++++++++--------------
>  fs/nfs/nfs4proc.c               |    6 -
>  fs/nfsd/nfs4state.c             |    6 -
>  fs/ocfs2/locks.c                |   10 +
>  include/linux/fs.h              |   13 +
>  include/trace/events/filelock.h |   16 +-
>  9 files changed, 252 insertions(+), 157 deletions(-)
> 
> --
> Signature
> 

Thanks Neil,

This looks great. I've gone ahead and replaced the set in locks-next
with this one. Unless we hear of any other problems, I'll plan to send a
PR to Linus when the merge window opens.

Cheers,
-- 
Jeff Layton <jlayton@kernel.org>