fat: remove i_alloc_sem abuse

Add a new rw_semaphore to protect bmap against truncate.  Previous
i_alloc_sem was abused for this, but it's going away in this series.

Note that we can't simply use i_mutex, given that the swapon code
calls ->bmap under it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/fat/file.c b/fs/fat/file.c
index 7018e1d8902d..a4a3a3c06436 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -429,8 +429,10 @@ int fat_setattr(struct dentry *dentry, struct iattr *attr)
         }
 
         if (attr->ia_valid & ATTR_SIZE) {
+                down_write(&MSDOS_I(inode)->truncate_lock);
                 truncate_setsize(inode, attr->ia_size);
                 fat_truncate_blocks(inode, attr->ia_size);
+                up_write(&MSDOS_I(inode)->truncate_lock);
         }
 
         setattr_copy(inode, attr);