linux-kernel - Re: [PATCH] block: add missing block_bio

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Message-ID: <20120130170548.GA3355@google.com>
Date:	Mon, 30 Jan 2012 09:05:48 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Namhyung Kim <namhyung@...il.com>
Cc:	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>, dm-devel@...hat.com
Subject: Re: [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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