diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c index 93bc4f83b73e..a52458435327 100644 --- a/fs/tracefs/event_inode.c +++ b/fs/tracefs/event_inode.c @@ -124,7 +124,17 @@ static inline void put_ei(struct eventfs_inode *ei) static inline void free_ei(struct eventfs_inode *ei) { if (ei) { + /* The ei should have no children if it is being freed. */ + WARN_ON_ONCE(!list_empty(&ei->children)); ei->is_freed = 1; + /* + * The SRCU iteration has a smp_rmb() to make sure it + * sees a child (that may have already been freed) + * before it reads is_free. If is_free is set, it must + * not use the child it acquired from ei->children, as + * the list may be used for SRCU. + */ + smp_wmb(); put_ei(ei); } } @@ -627,6 +637,20 @@ static int eventfs_iterate(struct file *file, struct dir_context *ctx) list_for_each_entry_srcu(ei_child, &ei->children, list, srcu_read_lock_held(&eventfs_srcu)) { + /* + * If the ei is being freed, then the ei->children may be + * being used as the rcu list, which means the next element + * may be garbage. The ei->is_free is set before switching + * the ei->children over to ei->rcu. The read memory barrier + * here makes sure the ei_child is read before is_free is + * updated. + * + * Matches the smp_wmb() in free_ei() + */ + smp_rmb(); + if (ei->is_freed) + return -EINVAL; + if (c > 0) { c--; continue; diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h index a4a7f8431aff..c61481d04c8e 100644 --- a/fs/tracefs/internal.h +++ b/fs/tracefs/internal.h @@ -46,11 +46,11 @@ struct eventfs_attr { * @ino: The saved inode number */ struct eventfs_inode { + struct list_head list; union { - struct list_head list; + struct list_head children; struct rcu_head rcu; }; - struct list_head children; const struct eventfs_entry *entries; const char *name; struct eventfs_attr *entry_attrs;