From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: bpf@vger.kernel.org, netdev@vger.kernel.org
Cc: "Martin KaFai Lau" <kafai@fb.com>,
"Hangbin Liu" <liuhangbin@gmail.com>,
"Jesper Dangaard Brouer" <brouer@redhat.com>,
"Magnus Karlsson" <magnus.karlsson@gmail.com>,
"Paul E . McKenney" <paulmck@kernel.org>,
"Jakub Kicinski" <kuba@kernel.org>,
"Toke Høiland-Jørgensen" <toke@redhat.com>
Subject: [PATCH bpf-next v5 01/19] rcu: Create an unrcu_pointer() to remove __rcu from a pointer
Date: Thu, 24 Jun 2021 18:05:51 +0200 [thread overview]
Message-ID: <20210624160609.292325-2-toke@redhat.com> (raw)
In-Reply-To: <20210624160609.292325-1-toke@redhat.com>
From: "Paul E. McKenney" <paulmck@kernel.org>
The xchg() and cmpxchg() functions are sometimes used to carry out RCU
updates. Unfortunately, this can result in sparse warnings for both
the old-value and new-value arguments, as well as for the return value.
The arguments can be dealt with using RCU_INITIALIZER():
old_p = xchg(&p, RCU_INITIALIZER(new_p));
But a sparse warning still remains due to assigning the __rcu pointer
returned from xchg to the (most likely) non-__rcu pointer old_p.
This commit therefore provides an unrcu_pointer() macro that strips
the __rcu. This macro can be used as follows:
old_p = unrcu_pointer(xchg(&p, RCU_INITIALIZER(new_p)));
Reported-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
include/linux/rcupdate.h | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 9455476c5ba2..d7895b81264e 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -363,6 +363,20 @@ static inline void rcu_preempt_sleep_check(void) { }
#define rcu_check_sparse(p, space)
#endif /* #else #ifdef __CHECKER__ */
+/**
+ * unrcu_pointer - mark a pointer as not being RCU protected
+ * @p: pointer needing to lose its __rcu property
+ *
+ * Converts @p from an __rcu pointer to a __kernel pointer.
+ * This allows an __rcu pointer to be used with xchg() and friends.
+ */
+#define unrcu_pointer(p) \
+({ \
+ typeof(*p) *_________p1 = (typeof(*p) *__force)(p); \
+ rcu_check_sparse(p, __rcu); \
+ ((typeof(*p) __force __kernel *)(_________p1)); \
+})
+
#define __rcu_access_pointer(p, space) \
({ \
typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
--
2.32.0
next prev parent reply other threads:[~2021-06-24 16:06 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-24 16:05 [PATCH bpf-next v5 00/19] Clean up and document RCU-based object protection for XDP and TC BPF Toke Høiland-Jørgensen
2021-06-24 16:05 ` Toke Høiland-Jørgensen [this message]
2021-06-24 16:05 ` [PATCH bpf-next v5 02/19] doc: Clarify and expand RCU updaters and corresponding readers Toke Høiland-Jørgensen
2021-06-24 16:05 ` [PATCH bpf-next v5 03/19] doc: Give XDP as example of non-obvious RCU reader/updater pairing Toke Høiland-Jørgensen
2021-06-24 16:05 ` [PATCH bpf-next v5 04/19] bpf: allow RCU-protected lookups to happen from bh context Toke Høiland-Jørgensen
2021-06-24 16:05 ` [PATCH bpf-next v5 05/19] xdp: add proper __rcu annotations to redirect map entries Toke Høiland-Jørgensen
2021-06-24 16:05 ` [PATCH bpf-next v5 06/19] sched: remove unneeded rcu_read_lock() around BPF program invocation Toke Høiland-Jørgensen
2021-06-24 16:05 ` [PATCH bpf-next v5 07/19] ena: remove rcu_read_lock() around XDP " Toke Høiland-Jørgensen
2021-06-24 16:05 ` [PATCH bpf-next v5 08/19] bnxt: " Toke Høiland-Jørgensen
2021-06-24 16:05 ` [PATCH bpf-next v5 09/19] thunderx: " Toke Høiland-Jørgensen
2021-06-24 16:06 ` [PATCH bpf-next v5 10/19] freescale: " Toke Høiland-Jørgensen
2021-06-24 16:06 ` [PATCH bpf-next v5 11/19] net: intel: " Toke Høiland-Jørgensen
2021-06-24 16:06 ` [PATCH bpf-next v5 12/19] marvell: " Toke Høiland-Jørgensen
2021-06-24 16:06 ` [PATCH bpf-next v5 13/19] mlx4: " Toke Høiland-Jørgensen
2021-06-24 16:06 ` [PATCH bpf-next v5 14/19] nfp: " Toke Høiland-Jørgensen
2021-06-24 16:06 ` [PATCH bpf-next v5 15/19] qede: " Toke Høiland-Jørgensen
2021-06-24 16:06 ` [PATCH bpf-next v5 16/19] sfc: " Toke Høiland-Jørgensen
2021-06-24 16:06 ` [PATCH bpf-next v5 17/19] netsec: " Toke Høiland-Jørgensen
2021-06-24 16:06 ` [PATCH bpf-next v5 18/19] stmmac: " Toke Høiland-Jørgensen
2021-06-24 16:06 ` [PATCH bpf-next v5 19/19] net: ti: " Toke Høiland-Jørgensen
2021-06-24 18:00 ` [PATCH bpf-next v5 00/19] Clean up and document RCU-based object protection for XDP and TC BPF patchwork-bot+netdevbpf
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