linux-kernel - [PATCH RFC v6 2/5] srcu: Add notrace variant of srcu

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Message-Id: <20180507204143.13061-3-joelaf@google.com>
Date:   Mon,  7 May 2018 13:41:40 -0700
From:   Joel Fernandes <joelaf@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zilstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Glexiner <tglx@...utronix.de>,
        Boqun Feng <boqun.feng@...il.com>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Fenguang Wu <fengguang.wu@...el.com>,
        Baohong Liu <baohong.liu@...el.com>,
        Vedang Patel <vedang.patel@...el.com>, kernel-team@...roid.com
Subject: [PATCH RFC v6 2/5] srcu: Add notrace variant of srcu_dereference

From: "Joel Fernandes (Google)" <joel@...lfernandes.org>

In the last patch in this series, we are making lockdep register hooks
onto the irq_{disable,enable} tracepoints. These tracepoints use the
_rcuidle tracepoint variant. In this series we switch the _rcuidle
tracepoint callers to use SRCU instead of sched-RCU. Inorder to
dereference the pointer to the probe functions, we could call
srcu_dereference, however this API will call back into lockdep to check
if the lock is held *before* the lockdep probe hooks have a chance to
run and annotate the IRQ enabled/disabled state.

For this reason we need a notrace variant of srcu_dereference since
otherwise we get lockdep splats. This patch adds the needed
srcu_dereference_notrace variant.

Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Peter Zilstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Tom Zanussi <tom.zanussi@...ux.intel.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Thomas Glexiner <tglx@...utronix.de>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Randy Dunlap <rdunlap@...radead.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Fenguang Wu <fengguang.wu@...el.com>
Cc: Baohong Liu <baohong.liu@...el.com>
Cc: Vedang Patel <vedang.patel@...el.com>
Cc: kernel-team@...roid.com
Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
 include/linux/srcu.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 2ec618979b20..a1c4947be877 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -135,6 +135,11 @@ static inline int srcu_read_lock_held(const struct srcu_struct *sp)
  */
 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
 
+/**
+ * srcu_dereference_notrace - no tracing and no lockdep calls from here
+ */
+#define srcu_dereference_notrace(p, sp) srcu_dereference_check((p), (sp), 1)
+
 /**
  * srcu_read_lock - register a new reader for an SRCU-protected structure.
  * @sp: srcu_struct in which to register the new reader.
-- 
2.17.0.441.gb46fe60e1d-goog