On Mon, 30 Apr 2018 18:41:59 -0700
Joel Fernandes <joe...@google.com> wrote:
> I'm able to reproduce a lockdep splat when CONFIG_PROVE_LOCKING=y and
> CONFIG_PREEMPTIRQ_EVENTS=y.
Needs more info in the change log. It also requires that
CONFIG_DEBUG_LOCKED=y is set.
Add this to the change log:
The issue was this:
Start with: 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.
This patch should be separate (as you had it before), and needs to be
submitted now because it already causes issues. We can add:
Cc: sta...@vger.kernel.org
Fixes: d59158162e032 ("tracing: Add support for preempt and irq enable/disable
events")
-- Steve
>
> $ echo 1 > /d/tracing/events/preemptirq/preempt_enable/enable
>
> Cc: Steven Rostedt <rost...@goodmis.org>
> Cc: Peter Zilstra <pet...@infradead.org>
> Cc: Ingo Molnar <mi...@redhat.com>
> Cc: Mathieu Desnoyers <mathieu.desnoy...@efficios.com>
> Cc: Tom Zanussi <tom.zanu...@linux.intel.com>
> Cc: Namhyung Kim <namhy...@kernel.org>
> Cc: Thomas Glexiner <t...@linutronix.de>
> Cc: Boqun Feng <boqun.f...@gmail.com>
> Cc: Paul McKenney <paul...@linux.vnet.ibm.com>
> Cc: Frederic Weisbecker <fweis...@gmail.com>
> Cc: Randy Dunlap <rdun...@infradead.org>
> Cc: Masami Hiramatsu <mhira...@kernel.org>
> Cc: Fenguang Wu <fengguang...@intel.com>
> Cc: Baohong Liu <baohong....@intel.com>
> Cc: Vedang Patel <vedang.pa...@intel.com>
> Cc: kernel-t...@android.com
> Signed-off-by: Joel Fernandes <joe...@google.com>
> ---
> kernel/softirq.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index 24d243ef8e71..47e2f61938c0 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);
> }
>
> /*
