From: Jianyu Zhan <jianyu.z...@emc.com>
I've met such a race conditon the same as what commit 3a198886
("sysfs: handle 'parent deleted before child added'") tackled.
The senario got triggered under a torturing test of quick disk
removal and plugging.
The forementioned commit 3a198886 didn't really fix this race,
it just narrows down the racy window.
A proper fix for this is to pin the parent kernfs_node on the
dir_entry creation point (sysfs_create_dir_ns), and to de-pin the parent
on the dir_entry deletion point(sysfs_remove_dir).
Though Tejun has added a comment in sysfs_remove_dir to warn such a
race and leave the option to upper layer. But wrt correct logic point,
I think it is good to add such pin behavior.
Note. another commit 26ea12de("kobject: grab an extra reference on kobject->sd
to allow duplicate deletes") also adds such a pin at the kobject layer.
But this commit tackles different issue - it pins an entry(not its parent)
after its creation, to allow duplicate deletions.
Signed-off-by: Jianyu Zhan <nasa4...@gmail.com>
---
fs/sysfs/dir.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 0b45ff4..0ac82cd 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -49,7 +49,12 @@ int sysfs_create_dir_ns(struct kobject *kobj, const void *ns)
else
parent = sysfs_root_kn;
- if (!parent)
+ /*
+ * We might race with the parent node removal.
+ * To avoid such race and for logic correctness,
+ * we pin the parent node here.
+ */
+ if (!sysfs_get(parent))
return -ENOENT;
kn = kernfs_create_dir_ns(parent, kobject_name(kobj),
@@ -94,6 +99,10 @@ void sysfs_remove_dir(struct kobject *kobj)
if (kn) {
WARN_ON_ONCE(kernfs_type(kn) != KERNFS_DIR);
+ /*
+ * Drop our pin on parent
+ */
+ sysfs_put(kn->parent);
kernfs_remove(kn);
}
}
--
2.0.1.472.g6f92e5f
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