Messages in this thread Patch in this message | | | Date | Tue, 1 May 2018 10:02:10 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH RFC v5 1/6] softirq: reorder trace_softirqs_on to prevent lockdep splat |
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On Mon, 30 Apr 2018 18:41:59 -0700 Joel Fernandes <joelaf@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: stable@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 <rostedt@goodmis.org> > Cc: Peter Zilstra <peterz@infradead.org> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > Cc: Tom Zanussi <tom.zanussi@linux.intel.com> > Cc: Namhyung Kim <namhyung@kernel.org> > Cc: Thomas Glexiner <tglx@linutronix.de> > Cc: Boqun Feng <boqun.feng@gmail.com> > Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> > Cc: Frederic Weisbecker <fweisbec@gmail.com> > Cc: Randy Dunlap <rdunlap@infradead.org> > Cc: Masami Hiramatsu <mhiramat@kernel.org> > Cc: Fenguang Wu <fengguang.wu@intel.com> > Cc: Baohong Liu <baohong.liu@intel.com> > Cc: Vedang Patel <vedang.patel@intel.com> > Cc: kernel-team@android.com > Signed-off-by: Joel Fernandes <joelaf@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); > } > > /*
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