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

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Date:   Mon, 30 Jan 2023 22:10:39 +1100
From:   Alistair Popple <apopple@...dia.com>
To:     Jason Gunthorpe <jgg@...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


Jason Gunthorpe <jgg@...dia.com> writes:

> 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?

Good point. Will add the following fix:

@@ -123,6 +123,7 @@ static int usnic_uiom_get_pages(unsigned long addr, size_t size, int writable,
 
 	vm_account_init_current(&uiomr->vm_account);
 	if (vm_account_pinned(&uiomr->vm_account, npages)) {
+		npages = 0;
 		ret = -ENOMEM;
 		goto out;
 	}

>
> Jason