softirq: Reorder trace_softirqs_on to prevent lockdep splat
PATCH 2/5 softirq: Reorder trace_softirqs_on to prevent lockdep splat
From: "Joel Fernandes (Google)" <[email protected]>
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 lockdepWhere preempt_count still has softirqs disabled, but current->softirqs_enabled is true, and we get a splat.
Cc Peter Zijlstra <[email protected]>
Cc Ingo Molnar <[email protected]>
Cc Linus Torvalds <[email protected]>
Cc Mathieu Desnoyers <[email protected]>
Cc Tom Zanussi <[email protected]>
Cc Namhyung Kim <[email protected]>
Cc Thomas Glexiner <[email protected]>
Cc Boqun Feng <[email protected]>
Cc Paul McKenney <[email protected]>
Cc Masami Hiramatsu <[email protected]>
Cc Todd Kjos <[email protected]>
Cc Erick Reyes <[email protected]>
Cc Julia Cartwright <[email protected]>
Cc Byungchul Park <[email protected]>
Reviewed-by Steven Rostedt (VMware) <[email protected]>
Fixes d59158162e032 ("tracing: Add support for preempt and irq enable/disable events")
Signed-off-by Joel Fernandes (Google) <[email protected]>
Signed-off-by Steven Rostedt (VMware) <[email protected]>
--- kernel/softirq.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
kernel/softirq.c +5 -1
@@ -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); }/*
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2.17.1