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Date:      Thu, 26 Apr 2007 21:36:33 +0200
From:      Hans Petter Selasky <hselasky@c2i.net>
To:        freebsd-hackers@freebsd.org
Subject:   msleep() on recursivly locked mutexes
Message-ID:  <200704262136.33196.hselasky@c2i.net>
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Hi,

In the new USB stack I have defined the following:

u_int32_t
mtx_drop_recurse(struct mtx *mtx)
{
        u_int32_t recurse_level = mtx->mtx_recurse;
        u_int32_t recurse_curr = recurse_level;

        mtx_assert(mtx, MA_OWNED);

        while(recurse_curr--) {
            mtx_unlock(mtx);
        }

        return recurse_level;
}

void
mtx_pickup_recurse(struct mtx *mtx, u_int32_t recurse_level)
{
        mtx_assert(mtx, MA_OWNED);

        while(recurse_level--) {
            mtx_lock(mtx);
        }
        return;
}

When I do a msleep() I do it like this:

        level = mtx_drop_recurse(ctd->p_mtx);

        error = msleep(ctd, ctd->p_mtx, 0, 
                       "config td sleep", timeout);

        mtx_pickup_recurse(ctd->p_mtx, level);

Are there any comments on integrating this functionality into msleep(), and 
adding mtx_drop_recurse() and mtx_pickup_recurse() to the FreeBSD kernel?

--HPS

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