mm: tiny-shmem nommu fix

The previous patch db203d53d474aa068984e409d807628f5841da1b ("mm:
tiny-shmem fix lock ordering: mmap_sem vs i_mutex") to fix the lock
ordering in tiny-shmem breaks shared anonymous and IPC memory on NOMMU
architectures because it was using the expanding truncate to signal ramfs
to allocate a physically contiguous RAM backing the inode (otherwise it is
unusable for "memory mapping" it to userspace).

However do_truncate is what caused the lock ordering error, due to it
taking i_mutex.  In this case, we can actually just call ramfs directly to
allocate memory for the mapping, rather than go via truncate.

Acked-by: David Howells <dhowells@redhat.com>
Acked-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/ramfs.h b/include/linux/ramfs.h
index b160fb18e8d6..37aaf2b39863 100644
--- a/include/linux/ramfs.h
+++ b/include/linux/ramfs.h
@@ -6,6 +6,7 @@ extern int ramfs_get_sb(struct file_system_type *fs_type,
          int flags, const char *dev_name, void *data, struct vfsmount *mnt);
 
 #ifndef CONFIG_MMU
+extern int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize);
 extern unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
                                                    unsigned long addr,
                                                    unsigned long len,