cifs: ensure that we always do cifsFileInfo_get under the spinlock

The readpages bug is a regression that was introduced in 6993f74a5.
This also fixes a couple of similar bugs in the uncached read and write
codepaths.

Also, prevent this sort of thing in the future by having cifsFileInfo_get
take the spinlock itself, and adding a _locked variant for use in places
that are already holding the lock. The _put code has always done that
so this makes for a less confusing interface.

Cc: <stable@vger.kernel.org> # 3.5.x
Reviewed-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>

2 files changed, 15 insertions, 8 deletions

diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index bcdf4d4420f1..497da5ce704c 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -765,13 +765,13 @@ struct cifs_io_parms {
  * Take a reference on the file private data. Must be called with
  * cifs_file_list_lock held.
  */
-static inline
-struct cifsFileInfo *cifsFileInfo_get(struct cifsFileInfo *cifs_file)
+static inline void
+cifsFileInfo_get_locked(struct cifsFileInfo *cifs_file)
 {
         ++cifs_file->count;
-        return cifs_file;
 }
 
+struct cifsFileInfo *cifsFileInfo_get(struct cifsFileInfo *cifs_file);
 void cifsFileInfo_put(struct cifsFileInfo *cifs_file);
 
 /*
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 07e9d41cade7..9154192b0683 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -284,6 +284,15 @@ cifs_new_fileinfo(__u16 fileHandle, struct file *file,
 
 static void cifs_del_lock_waiters(struct cifsLockInfo *lock);
 
+struct cifsFileInfo *
+cifsFileInfo_get(struct cifsFileInfo *cifs_file)
+{
+        spin_lock(&cifs_file_list_lock);
+        cifsFileInfo_get_locked(cifs_file);
+        spin_unlock(&cifs_file_list_lock);
+        return cifs_file;
+}
+
 /*
  * Release a reference on the file private data. This may involve closing
  * the filehandle out on the server. Must be called without holding
@@ -1562,7 +1571,7 @@ struct cifsFileInfo *find_readable_file(struct cifsInodeInfo *cifs_inode,
                         if (!open_file->invalidHandle) {
                                 /* found a good file */
                                 /* lock it so it will not be closed on us */
-                                cifsFileInfo_get(open_file);
+                                cifsFileInfo_get_locked(open_file);
                                 spin_unlock(&cifs_file_list_lock);
                                 return open_file;
                         } /* else might as well continue, and look for
@@ -1614,7 +1623,7 @@ refind_writable:
                 if (OPEN_FMODE(open_file->f_flags) & FMODE_WRITE) {
                         if (!open_file->invalidHandle) {
                                 /* found a good writable file */
-                                cifsFileInfo_get(open_file);
+                                cifsFileInfo_get_locked(open_file);
                                 spin_unlock(&cifs_file_list_lock);
                                 return open_file;
                         } else {
@@ -1631,7 +1640,7 @@ refind_writable:
 
         if (inv_file) {
                 any_available = false;
-                cifsFileInfo_get(inv_file);
+                cifsFileInfo_get_locked(inv_file);
         }
 
         spin_unlock(&cifs_file_list_lock);
@@ -3082,8 +3091,6 @@ static int cifs_readpages(struct file *file, struct address_space *mapping,
                         break;
                 }
 
-                spin_lock(&cifs_file_list_lock);
-                spin_unlock(&cifs_file_list_lock);
                 rdata->cfile = cifsFileInfo_get(open_file);
                 rdata->mapping = mapping;
                 rdata->offset = offset;