Alexander Kapshuk wrote on Thu, Jun 18, 2020:
> Address sparse nonderef rcu warnings:
> net/9p/client.c:790:17: warning: incorrect type in argument 1 (different
> address spaces)
> net/9p/client.c:790:17: expected struct spinlock [usertype] *lock
> net/9p/client.c:790:17: got struct spinlock [noderef] <asn:4> *
> net/9p/client.c:792:48: warning: incorrect type in argument 1 (different
> address spaces)
> net/9p/client.c:792:48: expected struct spinlock [usertype] *lock
> net/9p/client.c:792:48: got struct spinlock [noderef] <asn:4> *
> net/9p/client.c:872:17: warning: incorrect type in argument 1 (different
> address spaces)
> net/9p/client.c:872:17: expected struct spinlock [usertype] *lock
> net/9p/client.c:872:17: got struct spinlock [noderef] <asn:4> *
> net/9p/client.c:874:48: warning: incorrect type in argument 1 (different
> address spaces)
> net/9p/client.c:874:48: expected struct spinlock [usertype] *lock
> net/9p/client.c:874:48: got struct spinlock [noderef] <asn:4> *
>
> Signed-off-by: Alexander Kapshuk <alexander.kaps...@gmail.com>
Thanks for this patch.
>From what I can see, there are tons of other parts of the code doing the
same noderef access pattern to access current->sighand->siglock and I
don't see much doing that.
A couple of users justify this by saying SLAB_TYPESAFE_BY_RCU ensures
we'll always get a usable lock which won't be reinitialized however we
access it... It's a bit dubious we'll get the same lock than unlock to
me, so I agree to some change though.
After a second look I think we should use something like the following:
if (!lock_task_sighand(current, &flags))
warn & skip (or some error, we'd null deref if this happened currently);
recalc_sigpending();
unlock_task_sighand(current, &flags);
As you can see, the rcu_read_lock() isn't kept until the unlock so I'm
not sure it will be enough to please sparse, but I've convinced myself
current->sighand cannot change while we hold the lock and there just are
too many such patterns in the kernel.
Please let me know if I missed something or if there is an ongoing
effort to change how this works; I'll wait for a v2.
--
Dominique
