linux-kernel - Re: [RFC PATCH 06/19] RDMA/usnic: convert to use vm

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Date:   Tue, 24 Jan 2023 10:41:28 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alistair Popple <apopple@...dia.com>
Cc:     linux-mm@...ck.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, jhubbard@...dia.com,
        tjmercier@...gle.com, hannes@...xchg.org, surenb@...gle.com,
        mkoutny@...e.com, daniel@...ll.ch,
        Christian Benvenuti <benve@...co.com>,
        Nelson Escobar <neescoba@...co.com>,
        Leon Romanovsky <leon@...nel.org>, linux-rdma@...r.kernel.org
Subject: Re: [RFC PATCH 06/19] RDMA/usnic: convert to use vm_account

On Tue, Jan 24, 2023 at 04:42:35PM +1100, Alistair Popple wrote:
> diff --git a/drivers/infiniband/hw/usnic/usnic_uiom.c b/drivers/infiniband/hw/usnic/usnic_uiom.c
> index c301b3b..250276e 100644
> --- a/drivers/infiniband/hw/usnic/usnic_uiom.c
> +++ b/drivers/infiniband/hw/usnic/usnic_uiom.c
> @@ -89,8 +89,6 @@ static int usnic_uiom_get_pages(unsigned long addr, size_t size, int writable,
>  	struct page **page_list;
>  	struct scatterlist *sg;
>  	struct usnic_uiom_chunk *chunk;
> -	unsigned long locked;
> -	unsigned long lock_limit;
>  	unsigned long cur_base;
>  	unsigned long npages;
>  	int ret;
> @@ -123,10 +121,8 @@ static int usnic_uiom_get_pages(unsigned long addr, size_t size, int writable,
>  	uiomr->owning_mm = mm = current->mm;
>  	mmap_read_lock(mm);
>  
> -	locked = atomic64_add_return(npages, &current->mm->pinned_vm);
> -	lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> -
> -	if ((locked > lock_limit) && !capable(CAP_IPC_LOCK)) {
> +	vm_account_init_current(&uiomr->vm_account);
> +	if (vm_account_pinned(&uiomr->vm_account, npages)) {
>  		ret = -ENOMEM;
>  		goto out;
>  	}

Is this error handling right? This driver tried to avoid the race by
using atomic64_add_return() but it means that the out label undoes the add:


> @@ -178,7 +174,8 @@ static int usnic_uiom_get_pages(unsigned long addr, size_t size, int writable,
>  out:
>  	if (ret < 0) {
>  		usnic_uiom_put_pages(chunk_list, 0);
> -		atomic64_sub(npages, &current->mm->pinned_vm);

Here

> +		vm_unaccount_pinned(&uiomr->vm_account, npages);
> +		vm_account_release(&uiomr->vm_account);

But with the new API we shouldn't call vm_unaccount_pinned() if
vm_account_pinned() doesn't succeed?

Jason