linux-kernel - Re: [PATCH 3/5] mm: Rework return value for copy_one

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Message-ID: <20200922100840.GA11679@redhat.com>
Date:   Tue, 22 Sep 2020 12:08:40 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Jason Gunthorpe <jgg@...pe.ca>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, Michal Hocko <mhocko@...e.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Kirill Shutemov <kirill@...temov.name>,
        Hugh Dickins <hughd@...gle.com>,
        Christoph Hellwig <hch@....de>,
        Andrea Arcangeli <aarcange@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Leon Romanovsky <leonro@...dia.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH 3/5] mm: Rework return value for copy_one_pte()

On 09/21, Peter Xu wrote:
>
> @@ -866,13 +877,18 @@ static int copy_pte_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
>  	pte_unmap_unlock(orig_dst_pte, dst_ptl);
>  	cond_resched();
>  
> -	if (entry.val) {
> -		if (add_swap_count_continuation(entry, GFP_KERNEL) < 0)
> +	switch (copy_ret) {
> +	case COPY_MM_SWAP_CONT:
> +		if (add_swap_count_continuation(data.entry, GFP_KERNEL) < 0)
>  			return -ENOMEM;
> -		progress = 0;
> +		break;

Note that you didn't clear copy_ret, it is still COPY_MM_SWAP_CONT,

> +	default:
> +		break;
>  	}
> +
>  	if (addr != end)
>  		goto again;

After that the main loop can stop again because of need_resched(), and
in this case add_swap_count_continuation(data.entry) will be called again?

Oleg.