[PATCH] VFS,fs/locks.c,NFSD4: add race_free posix_lock_file_conf() interface

Lockd and the NFSv4 server both exercise a race condition where
posix_test_lock() is called either before or after posix_lock_file() to
deal with a denied lock request due to a conflicting lock.

Remove the race condition for the NFSv4 server by adding a new conflicting
lock parameter to __posix_lock_file() , changing the name to
__posix_lock_file_conf().

Keep posix_lock_file() interface, add posix_lock_conf() interface, both
call __posix_lock_file_conf().

[akpm@osdl.org: Put the EXPORT_SYMBOL() where it belongs]
Signed-off-by: Andy Adamson <andros@citi.umich.edu>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 25 insertions, 8 deletions

diff --git a/fs/locks.c b/fs/locks.c
index 4badf6a0e7b..4d9e71d43e7 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -792,9 +792,7 @@ out:
         return error;
 }
 
-EXPORT_SYMBOL(posix_lock_file);
-
-static int __posix_lock_file(struct inode *inode, struct file_lock *request)
+static int __posix_lock_file_conf(struct inode *inode, struct file_lock *request, struct file_lock *conflock)
 {
         struct file_lock *fl;
         struct file_lock *new_fl, *new_fl2;
@@ -818,6 +816,8 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request)
                                 continue;
                         if (!posix_locks_conflict(request, fl))
                                 continue;
+                        if (conflock)
+                                locks_copy_lock(conflock, fl);
                         error = -EAGAIN;
                         if (!(request->fl_flags & FL_SLEEP))
                                 goto out;
@@ -987,8 +987,24 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request)
  */
 int posix_lock_file(struct file *filp, struct file_lock *fl)
 {
-        return __posix_lock_file(filp->f_dentry->d_inode, fl);
+        return __posix_lock_file_conf(filp->f_dentry->d_inode, fl, NULL);
+}
+EXPORT_SYMBOL(posix_lock_file);
+
+/**
+ * posix_lock_file_conf - Apply a POSIX-style lock to a file
+ * @filp: The file to apply the lock to
+ * @fl: The lock to be applied
+ * @conflock: Place to return a copy of the conflicting lock, if found.
+ *
+ * Except for the conflock parameter, acts just like posix_lock_file.
+ */
+int posix_lock_file_conf(struct file *filp, struct file_lock *fl,
+                        struct file_lock *conflock)
+{
+        return __posix_lock_file_conf(filp->f_dentry->d_inode, fl, conflock);
 }
+EXPORT_SYMBOL(posix_lock_file_conf);
 
 /**
  * posix_lock_file_wait - Apply a POSIX-style lock to a file
@@ -1004,7 +1020,7 @@ int posix_lock_file_wait(struct file *filp, struct file_lock *fl)
         int error;
         might_sleep ();
         for (;;) {
-                error = __posix_lock_file(filp->f_dentry->d_inode, fl);
+                error = posix_lock_file(filp, fl);
                 if ((error != -EAGAIN) || !(fl->fl_flags & FL_SLEEP))
                         break;
                 error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
@@ -1076,7 +1092,7 @@ int locks_mandatory_area(int read_write, struct inode *inode,
         fl.fl_end = offset + count - 1;
 
         for (;;) {
-                error = __posix_lock_file(inode, &fl);
+                error = __posix_lock_file_conf(inode, &fl, NULL);
                 if (error != -EAGAIN)
                         break;
                 if (!(fl.fl_flags & FL_SLEEP))
@@ -1689,7 +1705,7 @@ again:
                 error = filp->f_op->lock(filp, cmd, file_lock);
         else {
                 for (;;) {
-                        error = __posix_lock_file(inode, file_lock);
+                        error = posix_lock_file(filp, file_lock);
                         if ((error != -EAGAIN) || (cmd == F_SETLK))
                                 break;
                         error = wait_event_interruptible(file_lock->fl_wait,
@@ -1832,7 +1848,7 @@ again:
                 error = filp->f_op->lock(filp, cmd, file_lock);
         else {
                 for (;;) {
-                        error = __posix_lock_file(inode, file_lock);
+                        error = posix_lock_file(filp, file_lock);
                         if ((error != -EAGAIN) || (cmd == F_SETLK64))
                                 break;
                         error = wait_event_interruptible(file_lock->fl_wait,
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9674679525f..ab67181a5a5 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -763,6 +763,7 @@ extern void locks_copy_lock(struct file_lock *, struct file_lock *);
 extern void locks_remove_posix(struct file *, fl_owner_t);
 extern void locks_remove_flock(struct file *);
 extern int posix_test_lock(struct file *, struct file_lock *, struct file_lock *);
+extern int posix_lock_file_conf(struct file *, struct file_lock *, struct file_lock *);
 extern int posix_lock_file(struct file *, struct file_lock *);
 extern int posix_lock_file_wait(struct file *, struct file_lock *);
 extern int posix_unblock_lock(struct file *, struct file_lock *);