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Re: [dm-devel] [PATCH] block: add missing block_bio_complete() tracepoint



On Mon, Jan 30, 2012 at 03:38:57PM +0900, Namhyung Kim wrote:
> 2012-01-29 6:41 PM, Namhyung Kim wrote:
> >The block_bio_complete() TP has been missed so long, so that bio-based
> >drivers haven't been able to trace its IO behavior. Add it.
> >
> >In some rare cases, such as loop_switch, @bio->bi_bdev can be NULL.
> >Thus convert it to TRACE_EVENT_CONDITION() as Steven suggested.
> >
> 
> Now I see that it seems TRACE_EVENT_CONDITION() can protect event
> tracing from such condition, but what about other users of the TP
> like blktrace? I think it'll still get NULL pointer dereference on
> bdev_get_queue() after the change, right? If so, convert to T_E_C()
> looks meaningless IMHO. Do I miss something?

Not really following, but the whole point of using
TRACE_EVENT_CONDITION() is avoiding the conditional jump when the TP
is disabled.  Whether the TP users need to test again / more isn't too
important.

Thanks.

-- 
tejun


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