• Steven Rostedt's avatar
    tracing: add same level recursion detection · 261842b7
    Steven Rostedt authored
    
    
    The tracing infrastructure allows for recursion. That is, an interrupt
    may interrupt the act of tracing an event, and that interrupt may very well
    perform its own trace. This is a recursive trace, and is fine to do.
    
    The problem arises when there is a bug, and the utility doing the trace
    calls something that recurses back into the tracer. This recursion is not
    caused by an external event like an interrupt, but by code that is not
    expected to recurse. The result could be a lockup.
    
    This patch adds a bitmask to the task structure that keeps track
    of the trace recursion. To find the interrupt depth, the following
    algorithm is used:
    
      level = hardirq_count() + softirq_count() + in_nmi;
    
    Here, level will be the depth of interrutps and softirqs, and even handles
    the nmi. Then the corresponding bit is set in the recursion bitmask.
    If the bit was already set, we know we had a recursion at the same level
    and we warn about it and fail the writing to the buffer.
    
    After the data has been committed to the buffer, we clear the bit.
    No atomics are needed. The only races are with interrupts and they reset
    the bitmask before returning anywy.
    
    [ Impact: detect same irq level trace recursion ]
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    261842b7
ftrace.h 13.9 KB