sysfs: store sysfs inode nrs in s_ino to avoid readdir oopses

Backport of
ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.22-rc1/2.6.22-rc1-mm1/broken-out/gregkh-driver-sysfs-allocate-inode-number-using-ida.patch

For regular files in sysfs, sysfs_readdir wants to traverse
sysfs_dirent->s_dentry->d_inode->i_ino to get to the inode number.
But, the dentry can be reclaimed under memory pressure, and there is
no synchronization with readdir.  This patch follows Tejun's scheme of
allocating and storing an inode number in the new s_ino member of a
sysfs_dirent, when dirents are created, and retrieving it from there
for readdir, so that the pointer chain doesn't have to be traversed.

Tejun's upstream patch uses a new-ish "ida" allocator which brings
along some extra complexity; this -stable patch has a brain-dead
incrementing counter which does not guarantee uniqueness, but because
sysfs doesn't hash inodes as iunique expects, uniqueness wasn't
guaranteed today anyway.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 11 insertions, 5 deletions

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 85a668680f82..17a819151b91 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -30,6 +30,14 @@ static struct dentry_operations sysfs_dentry_ops = {
         .d_iput         = sysfs_d_iput,
 };
 
+static unsigned int sysfs_inode_counter;
+ino_t sysfs_get_inum(void)
+{
+        if (unlikely(sysfs_inode_counter < 3))
+                sysfs_inode_counter = 3;
+        return sysfs_inode_counter++;
+}
+
 /*
  * Allocates a new sysfs_dirent and links it to the parent sysfs_dirent
  */
@@ -41,6 +49,7 @@ static struct sysfs_dirent * __sysfs_new_dirent(void * element)
         if (!sd)
                 return NULL;
 
+        sd->s_ino = sysfs_get_inum();
         atomic_set(&sd->s_count, 1);
         atomic_set(&sd->s_event, 1);
         INIT_LIST_HEAD(&sd->s_children);
@@ -509,7 +518,7 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
 
         switch (i) {
                 case 0:
-                        ino = dentry->d_inode->i_ino;
+                        ino = parent_sd->s_ino;
                         if (filldir(dirent, ".", 1, i, ino, DT_DIR) < 0)
                                 break;
                         filp->f_pos++;
@@ -538,10 +547,7 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
 
                                 name = sysfs_get_name(next);
                                 len = strlen(name);
-                                if (next->s_dentry)
-                                        ino = next->s_dentry->d_inode->i_ino;
-                                else
-                                        ino = iunique(sysfs_sb, 2);
+                                ino = next->s_ino;
 
                                 if (filldir(dirent, name, len, filp->f_pos, ino,
                                                  dt_type(next)) < 0)