• Steven Rostedt (VMware)'s avatar
    tracing: Add tracing_check_open_get_tr() · 8530dec6
    Steven Rostedt (VMware) authored
    Currently, most files in the tracefs directory test if tracing_disabled is
    set. If so, it should return -ENODEV. The tracing_disabled is called when
    tracing is found to be broken. Originally it was done in case the ring
    buffer was found to be corrupted, and we wanted to prevent reading it from
    crashing the kernel. But it's also called if a tracing selftest fails on
    boot. It's a one way switch. That is, once it is triggered, tracing is
    disabled until reboot.
    
    As most tracefs files can also be used by instances in the tracefs
    directory, they need to be carefully done. Each instance has a trace_array
    associated to it, and when the instance is removed, the trace_array is
    freed. But if an instance is opened with a reference to the trace_array,
    then it requires looking up the trace_array to get its ref counter (as there
    could be a race with it being deleted and the open itself). Once it is
    found, a reference is added to prevent the instance from being removed (and
    the trace_array associated with it freed).
    
    Combine the two checks (tracing_disabled and trace_array_get()) into a
    single helper function. This will also make it easier to add lockdown to
    tracefs later.
    
    Link: http://lkml.kernel.org/r/20191011135458.7399da44@gandalf.local.homeSigned-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
    8530dec6
trace_events_hist.c 150 KB