linux-kernel - [PATCH AUTOSEL 4.14 048/105] rcu: Force inlining of rcu_read

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Date:   Mon, 15 Jul 2019 10:27:42 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Waiman Long <longman@...hat.com>,
        "Paul E . McKenney" <paulmck@...ux.ibm.com>,
        Sasha Levin <sashal@...nel.org>, rcu@...r.kernel.org
Subject: [PATCH AUTOSEL 4.14 048/105] rcu: Force inlining of rcu_read_lock()

From: Waiman Long <longman@...hat.com>

[ Upstream commit 6da9f775175e516fc7229ceaa9b54f8f56aa7924 ]

When debugging options are turned on, the rcu_read_lock() function
might not be inlined. This results in lockdep's print_lock() function
printing "rcu_read_lock+0x0/0x70" instead of rcu_read_lock()'s caller.
For example:

[   10.579995] =============================
[   10.584033] WARNING: suspicious RCU usage
[   10.588074] 4.18.0.memcg_v2+ #1 Not tainted
[   10.593162] -----------------------------
[   10.597203] include/linux/rcupdate.h:281 Illegal context switch in
RCU read-side critical section!
[   10.606220]
[   10.606220] other info that might help us debug this:
[   10.606220]
[   10.614280]
[   10.614280] rcu_scheduler_active = 2, debug_locks = 1
[   10.620853] 3 locks held by systemd/1:
[   10.624632]  #0: (____ptrval____) (&type->i_mutex_dir_key#5){.+.+}, at: lookup_slow+0x42/0x70
[   10.633232]  #1: (____ptrval____) (rcu_read_lock){....}, at: rcu_read_lock+0x0/0x70
[   10.640954]  #2: (____ptrval____) (rcu_read_lock){....}, at: rcu_read_lock+0x0/0x70

These "rcu_read_lock+0x0/0x70" strings are not providing any useful
information.  This commit therefore forces inlining of the rcu_read_lock()
function so that rcu_read_lock()'s caller is instead shown.

Signed-off-by: Waiman Long <longman@...hat.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 include/linux/rcupdate.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index f960c85cd9ec..8d570190e9b4 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -622,7 +622,7 @@ static inline void rcu_preempt_sleep_check(void) { }
  * read-side critical sections may be preempted and they may also block, but
  * only when acquiring spinlocks that are subject to priority inheritance.
  */
-static inline void rcu_read_lock(void)
+static __always_inline void rcu_read_lock(void)
 {
 	__rcu_read_lock();
 	__acquire(RCU);
-- 
2.20.1