kernfs: fix ino wrap-around detection

When the 32bit ino wraps around, kernfs increments the generation number to distinguish reused ino instances. The wrap-around detection tests whether the allocated ino is lower than what the cursor but the cursor is pointing to the next ino to allocate so the condition never triggers. Fix it by remembering the last ino and comparing against that. Signed-off-by: Tejun Heo <[email protected]> Reviewed-by: Greg Kroah-Hartman <[email protected]> Fixes: 4a3ef68 ("kernfs: implement i_generation") Cc: Namhyung Kim <[email protected]> Cc: [email protected] # v4.14+
ashr · Nov 12, 2019 · e23f568 · e23f568
1 parent d671fa6
commit e23f568
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Showing 2 changed files with 3 additions and 3 deletions.
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
@@ -622,7 +622,6 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
 {
 	struct kernfs_node *kn;
 	u32 gen;
-	int cursor;
 	int ret;
 
 	name = kstrdup_const(name, GFP_KERNEL);
@@ -635,11 +634,11 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
 
 	idr_preload(GFP_KERNEL);
 	spin_lock(&kernfs_idr_lock);
-	cursor = idr_get_cursor(&root->ino_idr);
 	ret = idr_alloc_cyclic(&root->ino_idr, kn, 1, 0, GFP_ATOMIC);
-	if (ret >= 0 && ret < cursor)
+	if (ret >= 0 && ret < root->last_ino)
 		root->next_generation++;
 	gen = root->next_generation;
+	root->last_ino = ret;
 	spin_unlock(&kernfs_idr_lock);
 	idr_preload_end();
 	if (ret < 0)

diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
@@ -187,6 +187,7 @@ struct kernfs_root {
 
 	/* private fields, do not use outside kernfs proper */
 	struct idr		ino_idr;
+	u32			last_ino;
 	u32			next_generation;
 	struct kernfs_syscall_ops *syscall_ops;