Re: CVS commit: src/sys

[Michael van Elst <mlelstv%serpens.de@localhost>]

On Thu, Aug 27, 2015 at 11:48:15AM +0200, J. Hannken-Illjes wrote:

>                 disk_busy(&dksc->sc_dkdev);
> +               mutex_exit(&dksc->sc_iolock);
>                 error = dkd->d_diskstart(dksc->sc_dev, bp);
> +               mutex_enter(&dksc->sc_iolock);
>                 if (error == EAGAIN) {
> +                       dksc->sc_deferred = bp;
>                         disk_unbusy(&dksc->sc_dkdev, 0, (bp->b_flags & B_READ));
>                         break;
>                 }
> 
> Looks racy: what if two threads run  dk_strategy() -> dk_start() and
> both get EAGAIN.  Will it leak a buffer when the second thread tries
> to save bp and dksc->sc_deferred already holds the buffer from the
> first thread?

Looks like it. sc_deferred probably needs to become a fcfs bufq.
Currently this could happen for the ld driver (others are not MP_SAFE).

It would be simpler if you could unget something into the original
bufq.



Greetings,
-- 
                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."