Re: [PATCH] block: add missing block_bio_complete() tracepoint
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Hi, 2012-01-31 2:05 AM, Tejun Heo wrote:
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.
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.
Thanks, Namhyung -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel