linux-kernel - Re: [PATCH] mm/hmm: replace hmm_update with mmu_notifier

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Date:   Wed, 24 Jul 2019 09:05:53 +0200
From:   Christoph Hellwig <hch@....de>
To:     Ralph Campbell <rcampbell@...dia.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        nouveau@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        Jérôme Glisse <jglisse@...hat.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Christoph Hellwig <hch@....de>, Ben Skeggs <bskeggs@...hat.com>
Subject: Re: [PATCH] mm/hmm: replace hmm_update with mmu_notifier_range

Looks good:

Reviewed-by: Christoph Hellwig <hch@....de>

One comment on a related cleanup:

>  	list_for_each_entry(mirror, &hmm->mirrors, list) {
>  		int rc;
>  
> -		rc = mirror->ops->sync_cpu_device_pagetables(mirror, &update);
> +		rc = mirror->ops->sync_cpu_device_pagetables(mirror, nrange);
>  		if (rc) {
> -			if (WARN_ON(update.blockable || rc != -EAGAIN))
> +			if (WARN_ON(mmu_notifier_range_blockable(nrange) ||
> +			    rc != -EAGAIN))
>  				continue;
>  			ret = -EAGAIN;
>  			break;

This magic handling of error seems odd.  I think we should merge rc and
ret into one variable and just break out if any error happens instead
or claiming in the comments -EAGAIN is the only valid error and then
ignoring all others here.