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From: joelaf@google.com (Joel Fernandes)
Subject: [PATCH v7 1/8] softirq: reorder trace_softirqs_on to prevent lockdep splat
Date: Wed, 23 May 2018 18:21:50 -0700	[thread overview]
Message-ID: <20180524012157.181277-2-joel@joelfernandes.org> (raw)
Message-ID: <20180524012150.kxXfF9t-XazJT1wbZyy_MXvqJEEIQKo7CiCdnxg3rzo@z> (raw)
In-Reply-To: <20180524012157.181277-1-joel@joelfernandes.org>

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

I'm able to reproduce a lockdep splat with config options:
CONFIG_PROVE_LOCKING=y,
CONFIG_DEBUG_LOCK_ALLOC=y and
CONFIG_PREEMPTIRQ_EVENTS=y

$ echo 1 > /d/tracing/events/preemptirq/preempt_enable/enable

[   26.112609] DEBUG_LOCKS_WARN_ON(current->softirqs_enabled)
[   26.112636] WARNING: CPU: 0 PID: 118 at kernel/locking/lockdep.c:3854
[...]
[   26.144229] Call Trace:
[   26.144926]  <IRQ>
[   26.145506]  lock_acquire+0x55/0x1b0
[   26.146499]  ? __do_softirq+0x46f/0x4d9
[   26.147571]  ? __do_softirq+0x46f/0x4d9
[   26.148646]  trace_preempt_on+0x8f/0x240
[   26.149744]  ? trace_preempt_on+0x4d/0x240
[   26.150862]  ? __do_softirq+0x46f/0x4d9
[   26.151930]  preempt_count_sub+0x18a/0x1a0
[   26.152985]  __do_softirq+0x46f/0x4d9
[   26.153937]  irq_exit+0x68/0xe0
[   26.154755]  smp_apic_timer_interrupt+0x271/0x280
[   26.156056]  apic_timer_interrupt+0xf/0x20
[   26.157105]  </IRQ>

The issue was this:

preempt_count = 1 << SOFTIRQ_SHIFT

	__local_bh_enable(cnt = 1 << SOFTIRQ_SHIFT) {
		if (softirq_count() == (cnt && SOFTIRQ_MASK)) {
			trace_softirqs_on() {
				current->softirqs_enabled = 1;
			}
		}
		preempt_count_sub(cnt) {
			trace_preempt_on() {
				tracepoint() {
					rcu_read_lock_sched() {
						// jumps into lockdep

Where preempt_count still has softirqs disabled, but
current->softirqs_enabled is true, and we get a splat.

Cc: stable at vger.kernel.org
Reviewed-by: Steven Rostedt (VMware) <rostedt at goodmis.org>
Fixes: d59158162e032 ("tracing: Add support for preempt and irq enable/disable events")
Signed-off-by: Joel Fernandes (Google) <joel at joelfernandes.org>
---
 kernel/softirq.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 177de3640c78..8a040bcaa033 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -139,9 +139,13 @@ static void __local_bh_enable(unsigned int cnt)
 {
 	lockdep_assert_irqs_disabled();
 
+	if (preempt_count() == cnt)
+		trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
+
 	if (softirq_count() == (cnt & SOFTIRQ_MASK))
 		trace_softirqs_on(_RET_IP_);
-	preempt_count_sub(cnt);
+
+	__preempt_count_sub(cnt);
 }
 
 /*
-- 
2.17.0.441.gb46fe60e1d-goog

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  reply	other threads:[~2018-05-24  1:21 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-24  1:21 [PATCH v7 0/8] Centralize and unify usage of preempt/irq tracepoints Joel Fernandes
2018-05-24  1:21 ` Joel Fernandes
2018-05-24  1:21 ` joelaf
2018-05-24  1:21 ` Joel Fernandes [this message]
2018-05-24  1:21   ` [PATCH v7 1/8] softirq: reorder trace_softirqs_on to prevent lockdep splat Joel Fernandes
2018-05-24  1:21   ` joelaf
2018-05-24  1:21 ` [PATCH v7 2/8] srcu: Add notrace variants of srcu_read_{lock,unlock} Joel Fernandes
2018-05-24  1:21   ` Joel Fernandes
2018-05-24  1:21   ` joelaf
2018-05-24  1:21 ` [PATCH v7 3/8] srcu: Add notrace variant of srcu_dereference Joel Fernandes
2018-05-24  1:21   ` Joel Fernandes
2018-05-24  1:21   ` joelaf
2018-05-24  1:21 ` [PATCH v7 4/8] trace/irqsoff: Split reset into separate functions Joel Fernandes
2018-05-24  1:21   ` Joel Fernandes
2018-05-24  1:21   ` joelaf
2018-05-24  1:21 ` [PATCH v7 5/8] tracepoint: Make rcuidle tracepoint callers use SRCU Joel Fernandes
2018-05-24  1:21   ` Joel Fernandes
2018-05-24  1:21   ` joelaf
2018-05-24  1:21 ` [PATCH v7 6/8] tracing: Centralize preemptirq tracepoints and unify their usage Joel Fernandes
2018-05-24  1:21   ` Joel Fernandes
2018-05-24  1:21   ` joelaf
2018-05-25 11:43   ` Namhyung Kim
2018-05-25 11:43     ` Namhyung Kim
2018-05-25 11:43     ` namhyung
2018-05-25 23:20     ` Joel Fernandes
2018-05-25 23:20       ` Joel Fernandes
2018-05-25 23:20       ` joel
2018-05-24  1:21 ` [PATCH v7 7/8] lib: Add module to simulate atomic sections for testing preemptoff tracers Joel Fernandes
2018-05-24  1:21   ` Joel Fernandes
2018-05-24  1:21   ` joelaf
2018-05-24  1:21 ` [PATCH v7 8/8] kselftests: Add tests for the preemptoff and irqsoff tracers Joel Fernandes
2018-05-24  1:21   ` Joel Fernandes
2018-05-24  1:21   ` joelaf

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