[PATCH] fuse: fix hang on SMP

Fuse didn't always call i_size_write() with i_mutex held which caused rare
hangs on SMP/32bit.  This bug has been present since fuse-2.2, well before
being merged into mainline.

The simplest solution is to protect i_size_write() with the per-connection
spinlock.  Using i_mutex for this purpose would require some restructuring of
the code and I'm not even sure it's always safe to acquire i_mutex in all
places i_size needs to be set.

Since most of vmtruncate is already duplicated for other reasons, duplicate
the remaining part as well, making all i_size_write() calls internal to fuse.

Using i_size_write() was unnecessary in fuse_init_inode(), since this function
is only called on a newly created locked inode.

Reported by a few people over the years, but special thanks to Dana Henriksen
who was persistent enough in helping me debug it.

Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 7d0a9aee01f2..8e106163aaed 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -109,6 +109,7 @@ static int fuse_remount_fs(struct super_block *sb, int *flags, char *data)
 
 void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr)
 {
+        struct fuse_conn *fc = get_fuse_conn(inode);
         if (S_ISREG(inode->i_mode) && i_size_read(inode) != attr->size)
                 invalidate_inode_pages(inode->i_mapping);
 
@@ -117,7 +118,9 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr)
         inode->i_nlink   = attr->nlink;
         inode->i_uid     = attr->uid;
         inode->i_gid     = attr->gid;
+        spin_lock(&fc->lock);
         i_size_write(inode, attr->size);
+        spin_unlock(&fc->lock);
         inode->i_blocks  = attr->blocks;
         inode->i_atime.tv_sec   = attr->atime;
         inode->i_atime.tv_nsec  = attr->atimensec;
@@ -130,7 +133,7 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr)
 static void fuse_init_inode(struct inode *inode, struct fuse_attr *attr)
 {
         inode->i_mode = attr->mode & S_IFMT;
-        i_size_write(inode, attr->size);
+        inode->i_size = attr->size;
         if (S_ISREG(inode->i_mode)) {
                 fuse_init_common(inode);
                 fuse_init_file_inode(inode);