linux-kernel - Re: [PATCH 3/3] aio_free_ring: don't do page

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Message-ID: <x49lhfinqcr.fsf@segfault.boston.devel.redhat.com>
Date:	Wed, 17 Jun 2015 14:26:28 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin LaHaise <bcrl@...ck.org>, linux-aio@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] aio_free_ring: don't do page_count(NULL)

Oleg Nesterov <oleg@...hat.com> writes:

> aio_free_ring() can actually see the NULL page in ->ring_pages[],
> this can happen if aio_setup_ring() fails.
>
> And in this case page_count(ctx->ring_pages[i]) can OOPS.
>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

I'm not sure the reformatting was necessary, but whatever.

Reviewed-by: Jeff Moyer <jmoyer@...hat.com>

> ---
>  fs/aio.c |    8 ++++----
>  1 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index b605ab2..666fbb8 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -292,12 +292,12 @@ static void aio_free_ring(struct kioctx *ctx)
>  	put_aio_ring_file(ctx);
>  
>  	for (i = 0; i < ctx->nr_pages; i++) {
> -		struct page *page;
> -		pr_debug("pid(%d) [%d] page->count=%d\n", current->pid, i,
> -				page_count(ctx->ring_pages[i]));
> -		page = ctx->ring_pages[i];
> +		struct page *page = ctx->ring_pages[i];
>  		if (!page)
>  			continue;
> +
> +		pr_debug("pid(%d) [%d] page->count=%d\n",
> +				current->pid, i, page_count(page));
>  		ctx->ring_pages[i] = NULL;
>  		put_page(page);
>  	}
--
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