| Message ID | 95cf587fe96127884e555f695fe519d50e63cc17.1605522868.git.pabeni@redhat.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [net-next] net: add annotation for sock_{lock,unlock}_fast | expand |
Hello, Thank you for the feedback! On Mon, 2020-11-16 at 23:27 +0100, Luc Van Oostenryck wrote: > > @@ -1606,10 +1607,12 @@ bool lock_sock_fast(struct sock *sk); > > */ > > static inline void unlock_sock_fast(struct sock *sk, bool slow) > > { > > - if (slow) > > + if (slow) { > > release_sock(sk); > > - else > > + __release(&sk->sk_lock.slock); > > The correct solution would be to annotate the declaration of > release_sock() with '__releases(&sk->sk_lock.slock)'. If I add such annotation to release_sock(), I'll get several sparse warnings for context imbalance (on each lock_sock()/release_sock() pair), unless I also add an '__acquires()' annotation to lock_sock(). The above does not look correct to me ?!? When release_sock() completes the socket spin lock is not held. The annotation added above is somewhat an artifact to let unlock_sock_fast() matches lock_sock_fast() from sparse perspective. I intentionally avoided changing the release_sock() annotation to avoid introducing more artifacts. The proposed schema is not 100% accurate, as it will also allow e.g. a really-not-fitting bh_lock_sock()/unlock_sock_fast() pair, but I could not come-up with anything better. Can we go with the schema I proposed? Thanks, Paolo
On Tue, Nov 17, 2020 at 09:38:45AM +0100, Paolo Abeni wrote: > Hello, > > Thank you for the feedback! > > On Mon, 2020-11-16 at 23:27 +0100, Luc Van Oostenryck wrote: > > > @@ -1606,10 +1607,12 @@ bool lock_sock_fast(struct sock *sk); > > > */ > > > static inline void unlock_sock_fast(struct sock *sk, bool slow) > > > { > > > - if (slow) > > > + if (slow) { > > > release_sock(sk); > > > - else > > > + __release(&sk->sk_lock.slock); > > > > The correct solution would be to annotate the declaration of > > release_sock() with '__releases(&sk->sk_lock.slock)'. > > If I add such annotation to release_sock(), I'll get several sparse > warnings for context imbalance (on each lock_sock()/release_sock() > pair), unless I also add an '__acquires()' annotation to lock_sock(). > > The above does not look correct to me ?!? When release_sock() completes > the socket spin lock is not held. Yes, that's fine, but I suppose it somehow releases the mutex that is taken in lock_sock_fast() when returning true, right? > The annotation added above is > somewhat an artifact to let unlock_sock_fast() matches lock_sock_fast() > from sparse perspective. I intentionally avoided changing > the release_sock() annotation to avoid introducing more artifacts. > > The proposed schema is not 100% accurate, as it will also allow e.g. a > really-not-fitting bh_lock_sock()/unlock_sock_fast() pair, but I could > not come-up with anything better. > > Can we go with the schema I proposed? Well, I suppose it's a first step. But can you then add a '__releases(...)' to unlock_sock_fast()? It's not needed by sparse because it's an inline function and sparse can then deduce it but it will help to see the pairing with lock_sock_fast() is OK. -- Luc
Hello, On Tue, 2020-11-17 at 17:58 +0100, Luc Van Oostenryck wrote: > On Tue, Nov 17, 2020 at 09:38:45AM +0100, Paolo Abeni wrote: > > Hello, > > > > Thank you for the feedback! > > > > On Mon, 2020-11-16 at 23:27 +0100, Luc Van Oostenryck wrote: > > > > @@ -1606,10 +1607,12 @@ bool lock_sock_fast(struct sock *sk); > > > > */ > > > > static inline void unlock_sock_fast(struct sock *sk, bool slow) > > > > { > > > > - if (slow) > > > > + if (slow) { > > > > release_sock(sk); > > > > - else > > > > + __release(&sk->sk_lock.slock); > > > > > > The correct solution would be to annotate the declaration of > > > release_sock() with '__releases(&sk->sk_lock.slock)'. > > > > If I add such annotation to release_sock(), I'll get several sparse > > warnings for context imbalance (on each lock_sock()/release_sock() > > pair), unless I also add an '__acquires()' annotation to lock_sock(). > > > > The above does not look correct to me ?!? When release_sock() completes > > the socket spin lock is not held. > > Yes, that's fine, but I suppose it somehow releases the mutex that > is taken in lock_sock_fast() when returning true, right? Well, it has mutex semantics, but does not really acquire any mutex. > > The annotation added above is > > somewhat an artifact to let unlock_sock_fast() matches lock_sock_fast() > > from sparse perspective. I intentionally avoided changing > > the release_sock() annotation to avoid introducing more artifacts. > > > > The proposed schema is not 100% accurate, as it will also allow e.g. a > > really-not-fitting bh_lock_sock()/unlock_sock_fast() pair, but I could > > not come-up with anything better. > > > > Can we go with the schema I proposed? > > Well, I suppose it's a first step. > But can you then add a '__releases(...)' to unlock_sock_fast()? > It's not needed by sparse because it's an inline function and sparse > can then deduce it but it will help to see the pairing with > lock_sock_fast() is OK. Ok, I'll send a v2 with such annotation. Thanks! Paolo
diff --git a/include/net/sock.h b/include/net/sock.h index 1d29aeae74fd..60d321c6b5a5 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1595,7 +1595,8 @@ void release_sock(struct sock *sk); SINGLE_DEPTH_NESTING) #define bh_unlock_sock(__sk) spin_unlock(&((__sk)->sk_lock.slock)) -bool lock_sock_fast(struct sock *sk); +bool lock_sock_fast(struct sock *sk) __acquires(&sk->sk_lock.slock); + /** * unlock_sock_fast - complement of lock_sock_fast * @sk: socket @@ -1606,10 +1607,12 @@ bool lock_sock_fast(struct sock *sk); */ static inline void unlock_sock_fast(struct sock *sk, bool slow) { - if (slow) + if (slow) { release_sock(sk); - else + __release(&sk->sk_lock.slock); + } else { spin_unlock_bh(&sk->sk_lock.slock); + } } /* Used by processes to "lock" a socket state, so that diff --git a/net/core/sock.c b/net/core/sock.c index 727ea1cc633c..9badbe7bb4e4 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -3078,7 +3078,7 @@ EXPORT_SYMBOL(release_sock); * * sk_lock.slock unlocked, owned = 1, BH enabled */ -bool lock_sock_fast(struct sock *sk) +bool lock_sock_fast(struct sock *sk) __acquires(&sk->sk_lock.slock) { might_sleep(); spin_lock_bh(&sk->sk_lock.slock); @@ -3096,6 +3096,7 @@ bool lock_sock_fast(struct sock *sk) * The sk_lock has mutex_lock() semantics here: */ mutex_acquire(&sk->sk_lock.dep_map, 0, 0, _RET_IP_); + __acquire(&sk->sk_lock.slock); local_bh_enable(); return true; }
The static checker is fooled by the non-static locking scheme implemented by the mentioned helpers. Let's make its life easier adding some unconditional annotation so that the helpers are now interpreted as a plain spinlock from sparse. Signed-off-by: Paolo Abeni <pabeni@redhat.com> --- include/net/sock.h | 9 ++++++--- net/core/sock.c | 3 ++- 2 files changed, 8 insertions(+), 4 deletions(-)