sysfs: Introduce sysfs_rename_mutex
Looking carefully at the rename code we have a subtle dependency
that the structure of sysfs not change while we are performing
a rename. If the parent directory of the object we are renaming
changes while the rename is being performed nasty things could
happen when we go to release our locks.
So introduce a sysfs_rename_mutex to prevent this highly
unlikely theoretical issue.
In addition hold sysfs_rename_mutex over all calls to
sysfs_get_dentry. Allowing sysfs_get_dentry to be simplified
in the future.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 1af963e..9fe83d2 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -15,6 +15,7 @@
#include "sysfs.h"
DEFINE_MUTEX(sysfs_mutex);
+DEFINE_MUTEX(sysfs_rename_mutex);
spinlock_t sysfs_assoc_lock = SPIN_LOCK_UNLOCKED;
static spinlock_t sysfs_ino_lock = SPIN_LOCK_UNLOCKED;
@@ -82,7 +83,7 @@
* down from there looking up dentry for each step.
*
* LOCKING:
- * Kernel thread context (may sleep)
+ * mutex_lock(sysfs_rename_mutex)
*
* RETURNS:
* Pointer to found dentry on success, ERR_PTR() value on error.
@@ -858,6 +859,8 @@
const char *dup_name = NULL;
int error;
+ mutex_lock(&sysfs_rename_mutex);
+
/* get the original dentry */
sd = kobj->sd;
old_dentry = sysfs_get_dentry(sd);
@@ -915,6 +918,7 @@
kfree(dup_name);
dput(old_dentry);
dput(new_dentry);
+ mutex_unlock(&sysfs_rename_mutex);
return error;
}
@@ -926,6 +930,7 @@
struct dentry *old_dentry = NULL, *new_dentry = NULL;
int error;
+ mutex_lock(&sysfs_rename_mutex);
BUG_ON(!sd->s_parent);
new_parent_sd = new_parent_kobj->sd ? new_parent_kobj->sd : &sysfs_root;
@@ -982,6 +987,7 @@
dput(new_parent);
dput(old_dentry);
dput(new_dentry);
+ mutex_unlock(&sysfs_rename_mutex);
return error;
}