| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.17 069/220] softirq: Reorder trace_softirqs_on to prevent lockdep splat | Date | Sun, 1 Jul 2018 18:21:33 +0200 |
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4.17-stable review patch. If anyone has any objections, please let me know.
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From: Joel Fernandes (Google) <joel@joelfernandes.org>
commit 1a63dcd8765bc8680481dc2f9acf6ef13cee6d27 upstream.
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.
Link: http://lkml.kernel.org/r/20180607201143.247775-1-joel@joelfernandes.org
Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> 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: Masami Hiramatsu <mhiramat@kernel.org> Cc: Todd Kjos <tkjos@google.com> Cc: Erick Reyes <erickreyes@google.com> Cc: Julia Cartwright <julia@ni.com> Cc: Byungchul Park <byungchul.park@lge.com> Cc: stable@vger.kernel.org Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Fixes: d59158162e032 ("tracing: Add support for preempt and irq enable/disable events") Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- kernel/softirq.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
--- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -139,9 +139,13 @@ static void __local_bh_enable(unsigned i { 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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