linux-kernel - Re: [PATCH] mm: mempolicy: fix potential pte_unmap

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Date:   Mon, 19 Oct 2020 12:50:34 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Shijie Luo <luoshijie1@...wei.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, mhocko@...e.com,
        linmiaohe@...wei.com, linfeilong@...wei.com
Subject: Re: [PATCH] mm: mempolicy: fix potential pte_unmap_unlock pte error

On Mon, Oct 19, 2020 at 03:48:53AM -0400, Shijie Luo wrote:
> When flags in queue_pages_pte_range don't have MPOL_MF_MOVE or MPOL_MF_MOVE_ALL
>  bits, code breaks and passing origin pte - 1 to pte_unmap_unlock seems like
> not a good idea.

I think the above is already explained below?

> queue_pages_pte_range can run in MPOL_MF_MOVE_ALL mode which doesn't migrate
> misplaced pages but returns with EIO when encountering such a page. Since
> commit a7f40cfe3b7a ("mm: mempolicy: make mbind() return -EIO when MPOL_MF_STRICT
>  is specified") and early break on the first pte in the range results in
> pte_unmap_unlock on an underflow pte. This can lead to lockups later on when
>  somebody  tries to lock the pte resp. page_table_lock again..
> 
> Fixes: a7f40cfe3b7a ("mm: mempolicy: make mbind() return -EIO when
> MPOL_MF_STRICT is specified")
> 
> Signed-off-by: Shijie Luo <luoshijie1@...wei.com>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>

Anyway, LGTM:

Reviewed-by: Oscar Salvador <osalvador@...e.de>

-- 
Oscar Salvador
SUSE L3