Messages in this thread Patch in this message | | | From | Jason Andryuk <> | Subject | [PATCH] kcmp: Comment get_file_raw_ptr() RCU usage | Date | Wed, 2 Feb 2022 10:17:34 -0500 |
| |
This usage of RCU appears wrong since the pointer is passed outside the RCU region. However, it is not dereferenced, so it is "okay". Leave a comment for the next reader.
Without a reference, these comparisons are racy, but even with their use inside an RCU region, the result could go stale.
Signed-off-by: Jason Andryuk <jandryuk@gmail.com> --- I was looking for examples of task_lookup_fd_rcu()/files_lookup_fd_rcu() and found this. It differed from the example given in Documentation/filesystems/files.rst, so I was initially confused. A comment seemed appropriate to avoid confusion.
kernel/kcmp.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/kernel/kcmp.c b/kernel/kcmp.c index 5353edfad8e1..4fb23f242e0f 100644 --- a/kernel/kcmp.c +++ b/kernel/kcmp.c @@ -63,6 +63,9 @@ get_file_raw_ptr(struct task_struct *task, unsigned int idx) { struct file *file; + /* This RCU locking is only present to silence warnings. The pointer + * value is only used for comparison and not dereferenced, so it is + * acceptable. */ rcu_read_lock(); file = task_lookup_fd_rcu(task, idx); rcu_read_unlock(); -- 2.34.1
| |