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    Subject[PATCH 6/7] lockdep: Print a nice description of simple irq inversion
    From: Steven Rostedt <srostedt@redhat.com>

    The lockdep output can be pretty cryptic, having a nice output
    can save a lot of head scratching. When a simple irq inversion scenario
    is detected by lockdep (lock A taken in interrupt context but also in
    thread context without disabling interrupts) we get the following output:

    other info that might help us debug this:
    Possible unsafe locking scenario:

    CPU0
    ----
    lock(lockA);
    <Interrupt>
    lock(lockA);

    *** DEADLOCK ***

    Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    ---
    kernel/lockdep.c | 20 ++++++++++++++++++++
    1 files changed, 20 insertions(+), 0 deletions(-)

    diff --git a/kernel/lockdep.c b/kernel/lockdep.c
    index b531c66..3b1ac92 100644
    --- a/kernel/lockdep.c
    +++ b/kernel/lockdep.c
    @@ -2158,6 +2158,24 @@ static void check_chain_key(struct task_struct *curr)
    #endif
    }

    +static void
    +print_usage_bug_scenario(struct held_lock *lock)
    +{
    + struct lock_class *class = hlock_class(lock);
    +
    + printk(" Possible unsafe locking scenario:\n\n");
    + printk(" CPU0\n");
    + printk(" ----\n");
    + printk(" lock(");
    + __print_lock_name(class);
    + printk(");\n");
    + printk(" <Interrupt>\n");
    + printk(" lock(");
    + __print_lock_name(class);
    + printk(");\n");
    + printk("\n *** DEADLOCK ***\n\n");
    +}
    +
    static int
    print_usage_bug(struct task_struct *curr, struct held_lock *this,
    enum lock_usage_bit prev_bit, enum lock_usage_bit new_bit)
    @@ -2186,6 +2204,8 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this,

    print_irqtrace_events(curr);
    printk("\nother info that might help us debug this:\n");
    + print_usage_bug_scenario(this);
    +
    lockdep_print_held_locks(curr);

    printk("\nstack backtrace:\n");
    --
    1.7.2.3



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