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mm: tiny-shmem nommu fix

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The previous patch db203d53d4 ("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>
This commit is contained in:
Nick Piggin 2008-10-02 14:50:16 -07:00 committed by Linus Torvalds
parent 6c1b7f680d
commit 4b19de6d1c
3 changed files with 8 additions and 1 deletions
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2
fs/ramfs/file-nommu.c
View file

@ -58,7 +58,7 @@ const struct inode_operations ramfs_file_inode_operations = {
* size 0 on the assumption that it's going to be used for an mmap of shared
* memory
*/
static int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
{
struct pagevec lru_pvec;
unsigned long npages, xpages, loop, limit;

1
include/linux/ramfs.h
View file

@ -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,

6
mm/tiny-shmem.c
View file

@ -80,6 +80,12 @@ struct file *shmem_file_setup(char *name, loff_t size, unsigned long flags)
inode->i_nlink = 0; /* It is unlinked */
init_file(file, shm_mnt, dentry, FMODE_WRITE | FMODE_READ,
&ramfs_file_operations);
#ifndef CONFIG_MMU
error = ramfs_nommu_expand_for_mapping(inode, size);
if (error)
goto close_file;
#endif
return file;
close_file: