locks: defer freeing locks in locks_delete_lock until after i_lock has been dropped

In commit 72f98e72551fa (locks: turn lock_flocks into a spinlock), we
moved from using the BKL to a global spinlock. With this change, we lost
the ability to block in the fl_release_private operation.

This is problematic for NFS (and probably some other filesystems as
well). Add a new list_head argument to locks_delete_lock. If that
argument is non-NULL, then queue any locks that we want to free to the
list instead of freeing them.

Then, add a new locks_dispose_list function that will walk such a list
and call locks_free_lock on them after the i_lock has been dropped.

Finally, change all of the callers of locks_delete_lock to pass in a
list_head, except for lease_modify. That function can be called long
after the i_lock has been acquired. Deferring the freeing of a lease
after unlocking it in that function is non-trivial until we overhaul
some of the spinlocking in the lease code.

Currently though, no filesystem that sets fl_release_private supports
leases, so this is not currently a problem. We'll eventually want to
make the same change in the lease code, but it needs a lot more work
before we can reasonably do so.

Acked-by: J. Bruce Fields <bfields@fieldses.org>
Signed-off-by: Jeff Layton <jlayton@primarydata.com>

1 files changed, 30 insertions, 8 deletions

diff --git a/fs/locks.c b/fs/locks.c
index 7dd4defb4d8d..4ce087cca501 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -247,6 +247,18 @@ void locks_free_lock(struct file_lock *fl)
 }
 EXPORT_SYMBOL(locks_free_lock);
 
+static void
+locks_dispose_list(struct list_head *dispose)
+{
+        struct file_lock *fl;
+
+        while (!list_empty(dispose)) {
+                fl = list_first_entry(dispose, struct file_lock, fl_block);
+                list_del_init(&fl->fl_block);
+                locks_free_lock(fl);
+        }
+}
+
 void locks_init_lock(struct file_lock *fl)
 {
         memset(fl, 0, sizeof(struct file_lock));
@@ -651,12 +663,16 @@ static void locks_unlink_lock(struct file_lock **thisfl_p)
  *
  * Must be called with i_lock held!
  */
-static void locks_delete_lock(struct file_lock **thisfl_p)
+static void locks_delete_lock(struct file_lock **thisfl_p,
+                              struct list_head *dispose)
 {
         struct file_lock *fl = *thisfl_p;
 
         locks_unlink_lock(thisfl_p);
-        locks_free_lock(fl);
+        if (dispose)
+                list_add(&fl->fl_block, dispose);
+        else
+                locks_free_lock(fl);
 }
 
 /* Determine if lock sys_fl blocks lock caller_fl. Common functionality
@@ -812,6 +828,7 @@ static int flock_lock_file(struct file *filp, struct file_lock *request)
         struct inode * inode = file_inode(filp);
         int error = 0;
         int found = 0;
+        LIST_HEAD(dispose);
 
         if (!(request->fl_flags & FL_ACCESS) && (request->fl_type != F_UNLCK)) {
                 new_fl = locks_alloc_lock();
@@ -834,7 +851,7 @@ static int flock_lock_file(struct file *filp, struct file_lock *request)
                 if (request->fl_type == fl->fl_type)
                         goto out;
                 found = 1;
-                locks_delete_lock(before);
+                locks_delete_lock(before, &dispose);
                 break;
         }
 
@@ -881,6 +898,7 @@ out:
         spin_unlock(&inode->i_lock);
         if (new_fl)
                 locks_free_lock(new_fl);
+        locks_dispose_list(&dispose);
         return error;
 }
 
@@ -894,6 +912,7 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
         struct file_lock **before;
         int error;
         bool added = false;
+        LIST_HEAD(dispose);
 
         /*
          * We may need two file_lock structures for this operation,
@@ -989,7 +1008,7 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
                         else
                                 request->fl_end = fl->fl_end;
                         if (added) {
-                                locks_delete_lock(before);
+                                locks_delete_lock(before, &dispose);
                                 continue;
                         }
                         request = fl;
@@ -1019,7 +1038,7 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
                                  * one (This may happen several times).
                                  */
                                 if (added) {
-                                        locks_delete_lock(before);
+                                        locks_delete_lock(before, &dispose);
                                         continue;
                                 }
                                 /*
@@ -1035,7 +1054,7 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
                                 locks_copy_lock(new_fl, request);
                                 request = new_fl;
                                 new_fl = NULL;
-                                locks_delete_lock(before);
+                                locks_delete_lock(before, &dispose);
                                 locks_insert_lock(before, request);
                                 added = true;
                         }
@@ -1097,6 +1116,7 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
                 locks_free_lock(new_fl);
         if (new_fl2)
                 locks_free_lock(new_fl2);
+        locks_dispose_list(&dispose);
         return error;
 }
 
@@ -1272,7 +1292,7 @@ int lease_modify(struct file_lock **before, int arg)
                         printk(KERN_ERR "locks_delete_lock: fasync == %p\n", fl->fl_fasync);
                         fl->fl_fasync = NULL;
                 }
-                locks_delete_lock(before);
+                locks_delete_lock(before, NULL);
         }
         return 0;
 }
@@ -2324,6 +2344,7 @@ void locks_remove_file(struct file *filp)
         struct inode * inode = file_inode(filp);
         struct file_lock *fl;
         struct file_lock **before;
+        LIST_HEAD(dispose);
 
         if (!inode->i_flock)
                 return;
@@ -2369,12 +2390,13 @@ void locks_remove_file(struct file *filp)
                                 fl->fl_type, fl->fl_flags,
                                 fl->fl_start, fl->fl_end);
 
-                        locks_delete_lock(before);
+                        locks_delete_lock(before, &dispose);
                         continue;
                 }
                 before = &fl->fl_next;
         }
         spin_unlock(&inode->i_lock);
+        locks_dispose_list(&dispose);
 }
 
 /**