linux-kernel - [PATCH tip/core/rcu 1/4] rcu: Eliminate BUG

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Date:   Sun, 11 Nov 2018 11:32:14 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>
Subject: [PATCH tip/core/rcu 1/4] rcu: Eliminate BUG_ON() for sync.c

The sync.c file has a number of calls to BUG_ON(), which panics the
kernel, which is not a good strategy for devices (like embedded) that
don't have a way to capture console output.  This commit therefore
changes these BUG_ON() calls to WARN_ON_ONCE(), but does so quite naively.

Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
Acked-by: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
---
 kernel/rcu/sync.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c
index 3f943efcf61c..a6ba446a9693 100644
--- a/kernel/rcu/sync.c
+++ b/kernel/rcu/sync.c
@@ -125,8 +125,7 @@ void rcu_sync_enter(struct rcu_sync *rsp)
 		rsp->gp_state = GP_PENDING;
 	spin_unlock_irq(&rsp->rss_lock);
 
-	BUG_ON(need_wait && need_sync);
-
+	WARN_ON_ONCE(need_wait && need_sync);
 	if (need_sync) {
 		gp_ops[rsp->gp_type].sync();
 		rsp->gp_state = GP_PASSED;
@@ -139,7 +138,7 @@ void rcu_sync_enter(struct rcu_sync *rsp)
 		 * Nobody has yet been allowed the 'fast' path and thus we can
 		 * avoid doing any sync(). The callback will get 'dropped'.
 		 */
-		BUG_ON(rsp->gp_state != GP_PASSED);
+		WARN_ON_ONCE(rsp->gp_state != GP_PASSED);
 	}
 }
 
@@ -166,8 +165,8 @@ static void rcu_sync_func(struct rcu_head *rhp)
 	struct rcu_sync *rsp = container_of(rhp, struct rcu_sync, cb_head);
 	unsigned long flags;
 
-	BUG_ON(rsp->gp_state != GP_PASSED);
-	BUG_ON(rsp->cb_state == CB_IDLE);
+	WARN_ON_ONCE(rsp->gp_state != GP_PASSED);
+	WARN_ON_ONCE(rsp->cb_state == CB_IDLE);
 
 	spin_lock_irqsave(&rsp->rss_lock, flags);
 	if (rsp->gp_count) {
@@ -225,7 +224,7 @@ void rcu_sync_dtor(struct rcu_sync *rsp)
 {
 	int cb_state;
 
-	BUG_ON(rsp->gp_count);
+	WARN_ON_ONCE(rsp->gp_count);
 
 	spin_lock_irq(&rsp->rss_lock);
 	if (rsp->cb_state == CB_REPLAY)
@@ -235,6 +234,6 @@ void rcu_sync_dtor(struct rcu_sync *rsp)
 
 	if (cb_state != CB_IDLE) {
 		gp_ops[rsp->gp_type].wait();
-		BUG_ON(rsp->cb_state != CB_IDLE);
+		WARN_ON_ONCE(rsp->cb_state != CB_IDLE);
 	}
 }
-- 
2.17.1