The branch main has been updated by melifaro: URL: https://cgit.FreeBSD.org/src/commit/?id=600eade2fb4faacfcd408a01140ef15f85f0c817
commit 600eade2fb4faacfcd408a01140ef15f85f0c817 Author: Alexander V. Chernikov <[email protected]> AuthorDate: 2021-02-16 20:12:58 +0000 Commit: Alexander V. Chernikov <[email protected]> CommitDate: 2021-02-16 20:14:50 +0000 Add ifa_try_ref() to simplify ifa handling inside epoch. More and more code migrates from lock-based protection to the NET_EPOCH umbrella. It requires some logic changes, including, notably, refcount handling. When we have an `ifa` pointer and we're running inside epoch we're guaranteed that this pointer will not be freed. However, the following case can still happen: * in thread 1 we drop to 0 refcount for ifa and schedule its deletion. * in thread 2 we use this ifa and reference it * destroy callout kicks in * unhappy user reports bug To address it, new `ifa_try_ref()` function is added, allowing to return failure when we try to reference `ifa` with 0 refcount. Additionally, existing `ifa_ref()` is enforced with `KASSERT` to provide cleaner error in such scenarious. Reviewed By: rstone, donner Differential Revision: https://reviews.freebsd.org/D28639 MFC after: 1 week --- sys/net/if.c | 12 +++++++++++- sys/net/if_var.h | 1 + 2 files changed, 12 insertions(+), 1 deletion(-) diff --git a/sys/net/if.c b/sys/net/if.c index c85cfab19bf6..948be6876b65 100644 --- a/sys/net/if.c +++ b/sys/net/if.c @@ -1857,8 +1857,18 @@ fail: void ifa_ref(struct ifaddr *ifa) { + u_int old; - refcount_acquire(&ifa->ifa_refcnt); + old = refcount_acquire(&ifa->ifa_refcnt); + KASSERT(old > 0, ("%s: ifa %p has 0 refs", __func__, ifa)); +} + +int +ifa_try_ref(struct ifaddr *ifa) +{ + + NET_EPOCH_ASSERT(); + return (refcount_acquire_if_not_zero(&ifa->ifa_refcnt)); } static void diff --git a/sys/net/if_var.h b/sys/net/if_var.h index 9ecdfb684296..291a7781d73c 100644 --- a/sys/net/if_var.h +++ b/sys/net/if_var.h @@ -577,6 +577,7 @@ struct ifaddr { struct ifaddr * ifa_alloc(size_t size, int flags); void ifa_free(struct ifaddr *ifa); void ifa_ref(struct ifaddr *ifa); +int ifa_try_ref(struct ifaddr *ifa); /* * Multicast address structure. This is analogous to the ifaddr _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/dev-commits-src-all To unsubscribe, send any mail to "[email protected]"
