fasync: re-organize fasync entry insertion to allow it under a spinlock

You currently cannot use "fasync_helper()" in an atomic environment to
insert a new fasync entry, because it will need to allocate the new
"struct fasync_struct".

Yet fcntl_setlease() wants to call this under lock_flocks(), which is in
the process of being converted from the BKL to a spinlock.

In order to fix this, this abstracts out the actual fasync list
insertion and the fasync allocations into functions of their own, and
teaches fs/locks.c to pre-allocate the fasync_struct entry.  That way
the actual list insertion can happen while holding the required
spinlock.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bfields@redhat.com: rebase on top of my changes to Arnd's patch]
Tested-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

1 files changed, 17 insertions, 1 deletions

diff --git a/fs/locks.c b/fs/locks.c
index 0391d2ff5a4e..85fd9ce1abae 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1505,6 +1505,7 @@ EXPORT_SYMBOL_GPL(vfs_setlease);
 int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
 {
         struct file_lock *fl;
+        struct fasync_struct *new;
         struct inode *inode = filp->f_path.dentry->d_inode;
         int error;
 
@@ -1512,12 +1513,25 @@ int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
         if (IS_ERR(fl))
                 return PTR_ERR(fl);
 
+        new = fasync_alloc();
+        if (!new) {
+                locks_free_lock(fl);
+                return -ENOMEM;
+        }
         lock_flocks();
         error = __vfs_setlease(filp, arg, &fl);
         if (error || arg == F_UNLCK)
                 goto out_unlock;
 
-        error = fasync_helper(fd, filp, 1, &fl->fl_fasync);
+        /*
+         * fasync_insert_entry() returns the old entry if any.
+         * If there was no old entry, then it used 'new' and
+         * inserted it into the fasync list. Clear new so that
+         * we don't release it here.
+         */
+        if (!fasync_insert_entry(fd, filp, &fl->fl_fasync, new))
+                new = NULL;
+
         if (error < 0) {
                 /* remove lease just inserted by setlease */
                 fl->fl_type = F_UNLCK | F_INPROGRESS;
@@ -1529,6 +1543,8 @@ int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
         error = __f_setown(filp, task_pid(current), PIDTYPE_PID, 0);
 out_unlock:
         unlock_flocks();
+        if (new)
+                fasync_free(new);
         return error;
 }