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    Subject[PATCH 3.18 38/39] tracing: Add condition check to RCU lockdep checks
    Date
    3.18-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

    commit a05d59a5673339ef6936d6940cdf68172ce75b9f upstream.

    The trace_tlb_flush() tracepoint can be called when a CPU is going offline.
    When a CPU is offline, RCU is no longer watching that CPU and since the
    tracepoint is protected by RCU, it must not be called. To prevent the
    tlb_flush tracepoint from being called when the CPU is offline, it was
    converted to a TRACE_EVENT_CONDITION where the condition checks if the
    CPU is online before calling the tracepoint.

    Unfortunately, this was not enough to stop lockdep from complaining about
    it. Even though the RCU protected code of the tracepoint will never be
    called, the condition is hidden within the tracepoint, and even though the
    condition prevents RCU code from being called, the lockdep checks are
    outside the tracepoint (this is to test tracepoints even when they are not
    enabled).

    Even though tracepoints should be checked to be RCU safe when they are not
    enabled, the condition should still be considered when checking RCU.

    Link: http://lkml.kernel.org/r/CA+icZUUGiGDoL5NU8RuxKzFjoLjEKRtUWx=JB8B9a0EQv-eGzQ@mail.gmail.com

    Fixes: 3a630178fd5f "tracing: generate RCU warnings even when tracepoints are disabled"
    Acked-by: Dave Hansen <dave@sr71.net>
    Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
    Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
    index e08e21e5f601..c72851328ca9 100644
    --- a/include/linux/tracepoint.h
    +++ b/include/linux/tracepoint.h
    @@ -173,7 +173,7 @@ extern void syscall_unregfunc(void);
    TP_PROTO(data_proto), \
    TP_ARGS(data_args), \
    TP_CONDITION(cond),,); \
    - if (IS_ENABLED(CONFIG_LOCKDEP)) { \
    + if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) { \
    rcu_read_lock_sched_notrace(); \
    rcu_dereference_sched(__tracepoint_##name.funcs);\
    rcu_read_unlock_sched_notrace(); \



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