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>

3 files changed, 7 insertions, 2 deletions

diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index 8276cc282dec..a975b4147e91 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -109,6 +109,7 @@ struct msdos_inode_info {
         int i_attrs;            /* unused attribute bits */
         loff_t i_pos;           /* on-disk position of directory entry or 0 */
         struct hlist_node i_fat_hash;   /* hash by i_location */
+        struct rw_semaphore truncate_lock; /* protect bmap against truncate */
         struct inode vfs_inode;
 };
 
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);
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index cb8d8391ac0b..3decce46c38f 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -224,9 +224,9 @@ static sector_t _fat_bmap(struct address_space *mapping, sector_t block)
         sector_t blocknr;
 
         /* fat_get_cluster() assumes the requested blocknr isn't truncated. */
-        down_read(&mapping->host->i_alloc_sem);
+        down_read(&MSDOS_I(mapping->host)->truncate_lock);
         blocknr = generic_block_bmap(mapping, block, fat_get_block);
-        up_read(&mapping->host->i_alloc_sem);
+        up_read(&MSDOS_I(mapping->host)->truncate_lock);
 
         return blocknr;
 }
@@ -510,6 +510,8 @@ static struct inode *fat_alloc_inode(struct super_block *sb)
         ei = kmem_cache_alloc(fat_inode_cachep, GFP_NOFS);
         if (!ei)
                 return NULL;
+
+        init_rwsem(&ei->truncate_lock);
         return &ei->vfs_inode;
 }