mm: tiny-shmem fix lock ordering: mmap_sem vs i_mutex

tiny-shmem calls do_truncate in shmem_file_setup.  do_truncate takes
i_mutex, and shmem_file_setup is called with mmap_sem held.  However
i_mutex nests outside mmap_sem.

Copy the code in shmem.c to avoid this problem.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Nick Piggin <npiggin@suse.de>
Reported-and-tested-by: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 15 deletions

diff --git a/mm/tiny-shmem.c b/mm/tiny-shmem.c
index ae532f501943..d17cb6f6ab10 100644
--- a/mm/tiny-shmem.c
+++ b/mm/tiny-shmem.c
@@ -65,31 +65,25 @@ struct file *shmem_file_setup(char *name, loff_t size, unsigned long flags)
         if (!dentry)
                 goto put_memory;
 
-        error = -ENOSPC;
-        inode = ramfs_get_inode(root->d_sb, S_IFREG | S_IRWXUGO, 0);
-        if (!inode)
-                goto put_dentry;
-
-        d_instantiate(dentry, inode);
         error = -ENFILE;
-        file = alloc_file(shm_mnt, dentry, FMODE_WRITE | FMODE_READ,
-                        &ramfs_file_operations);
+        file = get_empty_filp();
         if (!file)
                 goto put_dentry;
 
-        inode->i_nlink = 0;     /* It is unlinked */
-
-        /* notify everyone as to the change of file size */
-        error = do_truncate(dentry, size, 0, file);
-        if (error < 0)
+        error = -ENOSPC;
+        inode = ramfs_get_inode(root->d_sb, S_IFREG | S_IRWXUGO, 0);
+        if (!inode)
                 goto close_file;
 
+        d_instantiate(dentry, inode);
+        inode->i_size = size;
+        inode->i_nlink = 0;     /* It is unlinked */
+        init_file(file, shm_mnt, dentry, FMODE_WRITE | FMODE_READ,
+                        &ramfs_file_operations);
         return file;
 
 close_file:
         put_filp(file);
-        return ERR_PTR(error);
-
 put_dentry:
         dput(dentry);
 put_memory: