• Steven Rostedt (Red Hat)'s avatar
    tracing: Have preempt(irqs)off trace preempt disabled functions · 5c89986e
    Steven Rostedt (Red Hat) authored
    commit cb86e053 upstream.
    
    Joel Fernandes reported that the function tracing of preempt disabled
    sections was not being reported when running either the preemptirqsoff or
    preemptoff tracers. This was due to the fact that the function tracer
    callback for those tracers checked if irqs were disabled before tracing. But
    this fails when we want to trace preempt off locations as well.
    
    Joel explained that he wanted to see funcitons where interrupts are enabled
    but preemption was disabled. The expected output he wanted:
    
       <...>-2265    1d.h1 3419us : preempt_count_sub <-irq_exit
       <...>-2265    1d..1 3419us : __do_softirq <-irq_exit
       <...>-2265    1d..1 3419us : msecs_to_jiffies <-__do_softirq
       <...>-2265    1d..1 3420us : irqtime_account_irq <-__do_softirq
       <...>-2265    1d..1 3420us : __local_bh_disable_ip <-__do_softirq
       <...>-2265    1..s1 3421us : run_timer_softirq <-__do_softirq
       <...>-2265    1..s1 3421us : hrtimer_run_pending <-run_timer_softirq
       <...>-2265    1..s1 3421us : _raw_spin_lock_irq <-run_timer_softirq
       <...>-2265    1d.s1 3422us : preempt_count_add <-_raw_spin_lock_irq
       <...>-2265    1d.s2 3422us : _raw_spin_unlock_irq <-run_timer_softirq
       <...>-2265    1..s2 3422us : preempt_count_sub <-_raw_spin_unlock_irq
       <...>-2265    1..s1 3423us : rcu_bh_qs <-__do_softirq
       <...>-2265    1d.s1 3423us : irqtime_account_irq <-__do_softirq
       <...>-2265    1d.s1 3423us : __local_bh_enable <-__do_softirq
    
    There's a comment saying that the irq disabled check is because there's a
    possible race that tracing_cpu may be set when the function is executed. But
    I don't remember that race. For now, I added a check for preemption being
    enabled too to not record the function, as there would be no race if that
    was the case. I need to re-investigate this, as I'm now thinking that the
    tracing_cpu will always be correct. But no harm in keeping the check for
    now, except for the slight performance hit.
    
    Link: http://lkml.kernel.org/r/1457770386-88717-1-git-send-email-agnel.joel@gmail.com
    
    Fixes: 5e6d2b9c "tracing: Use one prologue for the preempt irqs off tracer function tracers"
    Cc: stable@vget.kernel.org # 2.6.37+
    Reported-by: default avatarJoel Fernandes <agnel.joel@gmail.com>
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
    5c89986e
trace_irqsoff.c 17.5 KB