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    Subject[PATCH 3.16 112/157] trace: Fix preempt_enable_no_resched() abuse
    3.16.72-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Peter Zijlstra <peterz@infradead.org>

    commit d6097c9e4454adf1f8f2c9547c2fa6060d55d952 upstream.

    Unless the very next line is schedule(), or implies it, one must not use
    preempt_enable_no_resched(). It can cause a preemption to go missing and
    thereby cause arbitrary delays, breaking the PREEMPT=y invariant.

    Link: http://lkml.kernel.org/r/20190423200318.GY14281@hirez.programming.kicks-ass.net

    Cc: Waiman Long <longman@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: the arch/x86 maintainers <x86@kernel.org>
    Cc: Davidlohr Bueso <dave@stgolabs.net>
    Cc: Tim Chen <tim.c.chen@linux.intel.com>
    Cc: huang ying <huang.ying.caritas@gmail.com>
    Cc: Roman Gushchin <guro@fb.com>
    Cc: Alexei Starovoitov <ast@kernel.org>
    Cc: Daniel Borkmann <daniel@iogearbox.net>
    Fixes: 2c2d7329d8af ("tracing/ftrace: use preempt_enable_no_resched_notrace in ring_buffer_time_stamp()")
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    kernel/trace/ring_buffer.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/kernel/trace/ring_buffer.c
    +++ b/kernel/trace/ring_buffer.c
    @@ -729,7 +729,7 @@ u64 ring_buffer_time_stamp(struct ring_b

    preempt_disable_notrace();
    time = rb_time_stamp(buffer);
    - preempt_enable_no_resched_notrace();
    + preempt_enable_notrace();

    return time;
    }
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