• Steven Rostedt's avatar
    tracing: reset ring buffer when removing modules with events · 9456f0fa
    Steven Rostedt authored
    Li Zefan found that there's a race using the event ids of events and
    modules. When a module is loaded, an event id is incremented. We only
    have 16 bits for event ids (65536) and there is a possible (but highly
    unlikely) race that we could load and unload a module that registers
    events so many times that the event id counter overflows.
    When it overflows, it then restarts and goes looking for available
    ids. An id is available if it was added by a module and released.
    The race is if you have one module add an id, and then is removed.
    Another module loaded can use that same event id. But if the old module
    still had events in the ring buffer, the new module's call back would
    get bogus data.  At best (and most likely) the output would just be
    garbage. But if the module for some reason used pointers (not recommended)
    then this could potentially crash.
    The safest thing to do is just reset the ring buffer if a module that
    registered events is removed.
    [ Impact: prevent unpredictable results of event id overflows ]
    Reported-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
    LKML-Reference: <49FEAFD0.30106@cn.fujitsu.com>
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>