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    Subject[PATCH RFC v5 1/6] softirq: reorder trace_softirqs_on to prevent lockdep splat
    Date
    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

    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);
    }

    /*
    --
    2.17.0.441.gb46fe60e1d-goog
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