[CIFS] Fix locking problem around some cifs uses of i_size write

Could cause hangs on smp systems in i_size_read on a cifs inode
whose size has been previously simultaneously updated from
different processes.

Thanks to Brian Wang for some great testing/debugging on this
hard problem.

Fixes kernel bugzilla #7903

CC: Shirish Pargoankar <shirishp@us.ibm.com>
CC: Shaggy <shaggy@us.ibm.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/fs/cifs/readdir.c b/fs/cifs/readdir.c
index c444798f074..44cfb528797 100644
--- a/fs/cifs/readdir.c
+++ b/fs/cifs/readdir.c
@@ -3,7 +3,7 @@
  *
  *   Directory search handling
  * 
- *   Copyright (C) International Business Machines  Corp., 2004, 2005
+ *   Copyright (C) International Business Machines  Corp., 2004, 2007
  *   Author(s): Steve French (sfrench@us.ibm.com)
  *
  *   This library is free software; you can redistribute it and/or modify
@@ -226,6 +226,7 @@ static void fill_in_inode(struct inode *tmp_inode, int new_buf_type,
                 atomic_set(&cifsInfo->inUse, 1);
         }
 
+        spin_lock(&tmp_inode->i_lock);
         if (is_size_safe_to_change(cifsInfo, end_of_file)) {
                 /* can not safely change the file size here if the 
                 client is writing to it due to potential races */
@@ -235,6 +236,7 @@ static void fill_in_inode(struct inode *tmp_inode, int new_buf_type,
         /* for this calculation, even though the reported blocksize is larger */
                 tmp_inode->i_blocks = (512 - 1 + allocation_size) >> 9;
         }
+        spin_unlock(&tmp_inode->i_lock);
 
         if (allocation_size < end_of_file)
                 cFYI(1, ("May be sparse file, allocation less than file size"));
@@ -355,6 +357,7 @@ static void unix_fill_in_inode(struct inode *tmp_inode,
         tmp_inode->i_gid = le64_to_cpu(pfindData->Gid);
         tmp_inode->i_nlink = le64_to_cpu(pfindData->Nlinks);
 
+        spin_lock(&tmp_inode->i_lock);
         if (is_size_safe_to_change(cifsInfo, end_of_file)) {
                 /* can not safely change the file size here if the 
                 client is writing to it due to potential races */
@@ -364,6 +367,7 @@ static void unix_fill_in_inode(struct inode *tmp_inode,
         /* for this calculation, not the real blocksize */
                 tmp_inode->i_blocks = (512 - 1 + num_of_bytes) >> 9;
         }
+        spin_unlock(&tmp_inode->i_lock);
 
         if (S_ISREG(tmp_inode->i_mode)) {
                 cFYI(1, ("File inode"));