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>

diff --git a/fs/locks.c b/fs/locks.c
index 7dd4def..4ce087c 100644 (file)
--- 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);
 }
 
 /**