linux-kernel - Re: [Patch 02/12] GRU - add user request to explicitly unload a gru context

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Date:	Mon, 8 Jun 2009 16:05:25 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	steiner@....com
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [Patch 02/12] GRU - add user request to explicitly unload a gru
 context

On Mon, 08 Jun 2009 12:16:50 -0500
steiner@....com wrote:

>  /*
> + * Free all kernel contexts that are not currently in use.
> + *   Returns 0 if all freed, else number of inuse context.
> + */
> +static int gru_free_kernel_contexts(void)
> +{
> +	struct gru_blade_state *bs;
> +	struct gru_thread_state *kgts;
> +	int bid, ret = 0;
> +
> +	for (bid = 0; bid < GRU_MAX_BLADES; bid++) {
> +		bs = gru_base[bid];
> +		if (!bs)
> +			continue;
> +		if (down_write_trylock(&bs->bs_kgts_sema)) {

trylocks are always lame - they add a rarely-executed code path where
bugs can lurk.  They're often an admission that the locking is screwed
up.

I don't know if the latter is true here, but it would be helpful to add
a comment explaining what's going on, and why this unusual and
troublesome locking primitive is being used.

> +			kgts = bs->bs_kgts;
> +			if (kgts && kgts->ts_gru)
> +				gru_unload_context(kgts, 0);
> +			kfree(kgts);
> +			bs->bs_kgts = NULL;
> +			up_write(&bs->bs_kgts_sema);

nit: the kfree() can be moved outside the locked region.

> +		} else {
> +			ret++;
> +		}
> +	}
> +	return ret;
> +}
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