linux-kernel - Re: [PATCH 33/36] IB/odp/hmm: add core infiniband structure and helper for ODP with HMM.

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Date:	Wed, 24 Jun 2015 16:59:56 +0300
From:	Haggai Eran <haggaie@...lanox.com>
To:	<jglisse@...hat.com>, <akpm@...ux-foundation.org>
CC:	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	<joro@...tes.org>, Mel Gorman <mgorman@...e.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"Johannes Weiner" <jweiner@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>,
	"Rik van Riel" <riel@...hat.com>, Dave Airlie <airlied@...hat.com>,
	Brendan Conoboy <blc@...hat.com>,
	Joe Donohue <jdonohue@...hat.com>,
	Duncan Poole <dpoole@...dia.com>,
	Sherry Cheung <SCheung@...dia.com>,
	Subhash Gutti <sgutti@...dia.com>,
	John Hubbard <jhubbard@...dia.com>,
	Mark Hairgrove <mhairgrove@...dia.com>,
	Lucien Dunning <ldunning@...dia.com>,
	"Cameron Buschardt" <cabuschardt@...dia.com>,
	Arvind Gopalakrishnan <arvindg@...dia.com>,
	Shachar Raindel <raindel@...lanox.com>,
	Liran Liss <liranl@...lanox.com>,
	Roland Dreier <roland@...estorage.com>,
	Ben Sander <ben.sander@....com>,
	Greg Stoner <Greg.Stoner@....com>,
	John Bridgman <John.Bridgman@....com>,
	Michael Mantor <Michael.Mantor@....com>,
	"Paul Blinzer" <Paul.Blinzer@....com>,
	Laurent Morichetti <Laurent.Morichetti@....com>,
	Alexander Deucher <Alexander.Deucher@....com>,
	Oded Gabbay <Oded.Gabbay@....com>, <linux-rdma@...r.kernel.org>
Subject: Re: [PATCH 33/36] IB/odp/hmm: add core infiniband structure and helper
 for ODP with HMM.

On 21/05/2015 23:23, jglisse@...hat.com wrote:
> +int ib_umem_odp_get(struct ib_ucontext *context, struct ib_umem *umem)
> +{
> +	struct mm_struct *mm = get_task_mm(current);
> +	struct ib_device *ib_device = context->device;
> +	struct ib_mirror *ib_mirror;
> +	struct pid *our_pid;
> +	int ret;
> +
> +	if (!mm || !ib_device->hmm_ready)
> +		return -EINVAL;
> +
> +	/* FIXME can this really happen ? */
No, following Yann Droneaud's patch 8abaae62f3fd ("IB/core: disallow
registering 0-sized memory region") ib_umem_get() checks against zero
sized umems.

> +	if (unlikely(ib_umem_start(umem) == ib_umem_end(umem)))
> +		return -EINVAL;
> +
> +	/* Prevent creating ODP MRs in child processes */
> +	rcu_read_lock();
> +	our_pid = get_task_pid(current->group_leader, PIDTYPE_PID);
> +	rcu_read_unlock();
> +	put_pid(our_pid);
> +	if (context->tgid != our_pid) {
> +		mmput(mm);
> +		return -EINVAL;
> +	}
> +
> +	umem->hugetlb = 0;
> +	umem->odp_data = kmalloc(sizeof(*umem->odp_data), GFP_KERNEL);
> +	if (umem->odp_data == NULL) {
> +		mmput(mm);
> +		return -ENOMEM;
> +	}
> +	umem->odp_data->private = NULL;
> +	umem->odp_data->umem = umem;
> +
> +	mutex_lock(&ib_device->hmm_mutex);
> +	/* Is there an existing mirror for this process mm ? */
> +	ib_mirror = ib_mirror_ref(context->ib_mirror);
> +	if (!ib_mirror)
> +		list_for_each_entry(ib_mirror, &ib_device->ib_mirrors, list) {
> +			if (ib_mirror->base.hmm->mm != mm)
> +				continue;
> +			ib_mirror = ib_mirror_ref(ib_mirror);
> +			break;
> +		}
> +
> +	if (ib_mirror == NULL ||
> +	    ib_mirror == list_first_entry(&ib_device->ib_mirrors,
> +					  struct ib_mirror, list)) {
Is the second check an attempt to check if the list_for_each_entry above
passed through all the entries and didn't break? Maybe I missing
something, but I think that would cause the ib_mirror to hold a pointer
such that ib_mirror->list == ib_mirrors (point to the list head), and
not to the first entry.

In any case, I think it would be more clear if you add another ib_mirror
variable for iterating the ib_mirrors list.

> +		/* We need to create a new mirror. */
> +		ib_mirror = kmalloc(sizeof(*ib_mirror), GFP_KERNEL);
> +		if (ib_mirror == NULL) {
> +			mutex_unlock(&ib_device->hmm_mutex);
> +			mmput(mm);
> +			return -ENOMEM;
> +		}
> +		kref_init(&ib_mirror->kref);
> +		init_rwsem(&ib_mirror->hmm_mr_rwsem);
> +		ib_mirror->umem_tree = RB_ROOT;
> +		ib_mirror->ib_device = ib_device;
> +
> +		ib_mirror->base.device = &ib_device->hmm_dev;
> +		ret = hmm_mirror_register(&ib_mirror->base);
> +		if (ret) {
> +			mutex_unlock(&ib_device->hmm_mutex);
> +			kfree(ib_mirror);
> +			mmput(mm);
> +			return ret;
> +		}
> +
> +		list_add(&ib_mirror->list, &ib_device->ib_mirrors);
> +		context->ib_mirror = ib_mirror_ref(ib_mirror);
> +	}
> +	mutex_unlock(&ib_device->hmm_mutex);
> +	umem->odp_data.ib_mirror = ib_mirror;
> +
> +	down_write(&ib_mirror->umem_rwsem);
> +	rbt_ib_umem_insert(&umem->odp_data->interval_tree, &mirror->umem_tree);
> +	up_write(&ib_mirror->umem_rwsem);
> +
> +	mmput(mm);
> +	return 0;
> +}

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