I'm able to reproduce a lockdep splat when CONFIG_PROVE_LOCKING=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 problem is the softirqs annotation in lockdep goes out of sync with the reality of the world that softirq is still off. This causes a lockdep splat because the preempt_count_sub can call into a preemptoff tracer or the trace events code, which inturn can call into lockdep *before* softirqs are really turned back on, which can cause a softirqs invalid annotation splat in lockdep. The same issue was fixed in local_bh_disable_ip which has a comment so: /* * The preempt tracer hooks into preempt_count_add and will break * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET * is set and before current->softirq_enabled is cleared. * We must manually increment preempt_count here and manually * call the trace_preempt_off later. */ I have done a similar change to the local_bh_enable path to fix it. Cc: Steven Rostedt <[email protected]> Cc: Peter Zilstra <[email protected]> Cc: Ingo Molnar <[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: Frederic Weisbecker <[email protected]> Cc: Randy Dunlap <[email protected]> Cc: Masami Hiramatsu <[email protected]> Cc: Fenguang Wu <[email protected]> Cc: Baohong Liu <[email protected]> Cc: Vedang Patel <[email protected]> Cc: [email protected] Signed-off-by: Joel Fernandes <[email protected]> --- 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
