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

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Message-ID: <CAOS58YP1F6_yBxRArcP4oyzAJVArLJB-ckjdXU35U1SNwi75XQ@mail.gmail.com>
Date:	Tue, 31 Jan 2012 02:39:47 -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

Hello,

On Mon, Jan 30, 2012 at 10:30 PM, Namhyung Kim <namhyung@...il.com> wrote:
> Right, but the point is it could make a NULL pointer dereference during
> evaluation of the argument of the TP AFAICS. I'm not sure about the TP
> implementation though, I think I was wrong - T_E_C() cannot protect us from
> it because it happens just before jumping to the TP, right?
>
> So I think we need a conditional jump (with the "likely" annotation) for
> this even when the TP is disabled.

Hmmm... still not following. Where the said NULL dereference happen?
TEC conditional is equivalent to "if (COND) TP;".  If you don't use
TEC, it'll be "if (COND) if (TP enabled) TP;".  With TEC, it will be
"if (TP enabled) if (COND) TP;".  There's no other difference.

Thanks.

-- 
tejun
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