• Steven Rostedt (Red Hat)'s avatar
    tracing: Have branch tracer use recursive field of task struct · 6224beb1
    Steven Rostedt (Red Hat) authored
    Fengguang Wu's tests triggered a bug in the branch tracer's start up
    test when CONFIG_DEBUG_PREEMPT set. This was because that config
    adds some debug logic in the per cpu field, which calls back into
    the branch tracer.
    
    The branch tracer has its own recursive checks, but uses a per cpu
    variable to implement it. If retrieving the per cpu variable calls
    back into the branch tracer, you can see how things will break.
    
    Instead of using a per cpu variable, use the trace_recursion field
    of the current task struct. Simply set a bit when entering the
    branch tracing and clear it when leaving. If the bit is set on
    entry, just don't do the tracing.
    
    There's also the case with lockdep, as the local_irq_save() called
    before the recursion can also trigger code that can call back into
    the function. Changing that to a raw_local_irq_save() will protect
    that as well.
    
    This prevents the recursion and the inevitable crash that follows.
    
    Link: http://lkml.kernel.org/r/20150630141803.GA28071@wfg-t540p.sh.intel.com
    
    Cc: stable@vger.kernel.org # 3.10+
    Reported-by: default avatarFengguang Wu <fengguang.wu@intel.com>
    Tested-by: default avatarFengguang Wu <fengguang.wu@intel.com>
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    6224beb1
trace.h 40.2 KB